Veterinary Advice Online - Taenia Tapeworm Life Cycle.
The tapeworm Genus Taenia
comprises many different important species of tapeworm parasite infesting dogs, cats, humans, rodents and livestock animal species.
Species of parasitic Taenia tapeworms important to human and animal medicine include:
Taenia saginata (known as 'the beef tapeworm') - the adult form of the tapeworm resides in the human intestine(technically making it as much a human tapeworm as a 'beef' or cattle tapeworm) and the juvenile stage of the tapeworm (the stage of the tapeworm life cycle contagious to humans) resides in the muscles or meat of cattle (and to a lesser extent buffalos, llamas, giraffes, sheep, goats and certain deer species);
Taenia solium (the pork tapeworm) - a very dangerous tapeworm species whose adult form resides in the human gut and whose lethal juvenile or larval form resides in the muscles and organs of pigs and people(this page contains loads of information on the dangerous Taenia solium pork tapeworm so read on);
Taenia pisiformis - a canine tapeworm whose larval form is carried by rabbits and hares;
Taenia ovis - a canine tapeworm whose larval form is carried in the muscles and hearts of sheep;
Taenia taeniaeformis - a tapeworm in cats whose larval form is carried by rodents such as rats, muskrats and voles;
Taenia hydatigena - a canine tapeworm whose larval form is carried by sheep, goats, pigs, cattle, deer and wild livestock ungulates;
Taenia multiceps - a canid (dog and dog-related species) tapeworm whose larval form isgenerally carried in the brains of sheep and goats (occasionally horses, rabbits and cattle);
Taenia crassiceps - a tapeworm of foxes or dogs whose juvenile stages are generally carried by rodent animals;
Taenia serialis - a fox and dog tapeworm carried by rabbits, hares or rodents.
Taenia brauni - a fox and dog tapeworm carried by gerbils.
The different species of Taenia all tend to be very species specific with regard to the animal hosts, both definitiveand intermediate (intermediate hosts and definitive hosts are discussed in section 1), that they will activelyinfest. For example, Taenia saginata: the beef tapeworm, will only infest humans (definitive host)and, for the most part, cattle (intermediate host). Likewise, Taenia pisiformis: one of the two major 'rabbit tapeworms', will only infest canine species (definitive host) and rabbits (intermediate host). Having said this, despite there being vastly differing kinds of host animals involved in each of the Taenia species' life cycles, the overall two-host life cycle structure of the various Taeniid species does seem to be similar in all cases. For this reason, the different Taenia species can all be discussed using a common Taenia life cycle diagram, which is what I have chosen to do (see section 1).
This Taenia tapeworm life cycles page contains a detailed, but simple-to-understand explanation of thecomplete Taeniid tapeworm life cycle. It comes complete with a full tapeworm life cycle diagram, which includesthe life cycles of each of the major Taenia species infesting dogs, cats, people, rodent and livestock animal species. Detailed explanation of the Taenia life cycle is included, with mention made about each of the individualTaenia species where applicable. Info on tapeworm symptoms and the significance of tapeworm infestation in both definitiveand intermediate host animals is included as well as information on treating and managing tapeworm infestationsin these hosts. In the final section (section 4) you'll find extensive information about the Taeniid tapeworms infesting humans, in particular the nasty pork tapeworm (T. solium) and the more benign beef tapeworm (T. saginata).
The Taenia Tapeworm Life Cycle - Contents:
1) The Taenia tapeworm life cycle diagram - a complete step-by-step diagram of the variouscommon Taenia tapeworm species infesting pet animals (dogs, cats) and people and their transmission via intermediate livestock and wild animal hosts.
Human tapeworm infestationand the development of adult Taenia saginata and Taenia solium tapeworm burdens is discussed, as isthe life-threatening condition caused by infestation with larval forms of the Taenia solium pork tapeworm: human 'cysticercosis'.
2) Taenia tapeworm symptoms and outcomes - the significance of Taenia infestations in intermediate and definitive host animals.
2a) Tapeworm symptoms in intermediate hosts.
2b) Tapeworm symptoms in definitive hosts.
3) Treatment and prevention of Taeniid tapeworm infestations in definitive host pets (dogs and cats).
This section contains information on the drugs and medications used to treat tapeworms in dogs and cats.
4) Some basics on human tapeworm infestations and the prevention of tapeworm disease (especially pork tapeworm cysticercosis) in people.
4a) Tapeworms in Humans 1 - Taenia saginata beef tapeworm.
4b) Tapeworms in Humans 2 - Taenia solium pork tapeworm.
4c) Tapeworms in Humans 3 - accidental, opportunistic human tapeworm infestations with other Taenia species.
A link to a small page on Taenia taeniaeformis tapeworms in cats.
1) The Taenia Tapeworm Life Cycles Diagram:
Taenia tapeworm life cycle diagram: This is a diagram of the life cycle of a typical Taenia tapeworm.
The diagram shows the complete cycle of a Taeniid tapeworm's existence - from egg to adult tapeworm to egg again (with the next generation of tapeworm eggs) - within the bodies of two different, yet both equally essential, host animal species:
1. the intermediate host animal and
2. the definitivehost carnivore (dog, cat or man).
Most major species of Taenia tapeworm are included in the diagram. By following the arrows,you can see which species of intermediate and definitive host animals each of the different Taenia speciespredominantly infests. For example: Taenia ovis infests the sheep and the dog. Taenia hydatigena infests a variety of hooved livestock intermediate host species (cattle, sheep, pigs), as well as the dog (definitive host). I elected to insert Taenia multiceps only underneath the sheep intermediate host because, even though cattle, rabbits and horses can be intermediate hosts for this Taeniid species, the sheep is by farthe predominant intermediate host.
The diagram also indicates which parts of the animal body the two main tapeworm stages (the juvenile or larvalstage, which infests the intermediate host animal, and the adult stage, which infests the definitive host animal) occupy.This organ-trophism (organ localisation) is particularly important to know with regard to the intermediate host (larval) stage of a Taenia tapeworm species because some understanding of the organs that are typically occupied by the tapeworm larva (e.g. liver, brain, muscle, eye, skin) will provide an important clue as to the tapeworm disease symptoms that might be expected in that intermediate host animal. For example, Taenia multiceps preferentially infests the brain of the intermediate host sheep, soinfested sheep could be expected to show signs of profound neurological disease (weakness, loss-of-balance, paralysis, circling, head-pressing, fitting, death). Knowing which intermediate host organs could carry the infective juvenile tapeworms is also important in preventing the definitive host animal from contracting adult tapeworms. If we know the intermediate host organs that must be consumed if the definitive host animal is to contract the adult tapeworms, then we can take steps to prevent such tapeworm transmission by preventing the definitive host animal from consuming such intermediate host body parts. For example, dogs catch the adult form of Taenia multiceps by eating the brains and muscles of infested sheep.
The Adult Tapeworm in the Definitive Host:
Various species of adult Taenia tapeworms live and feed in the small intestines of such host animals as the dog,cat and human. These carnivorous host animals are termed definitive hosts with regard to their respectiveTaenia tapeworm life cycles because they are the hosts that their parasitic Taenia tapeworm species was intended for and that the tapeworm organism reaches adulthood and sexual maturity in. For example, the human isthe definitive host animal for the Taenia solium and Taenia saginata tapeworms, not the dog nor the cat. The cat is the sole definitive host animal for Taenia taeniaeformis.
The body of an adult Taeniid tapeworm is made up of hundreds to thousands of individual segments, termed proglottids. These segments progress in size and maturity as one travels down the tapeworm's body: ranging from very tiny (those proglottids nearest the scolex or 'head' of the tapeworm) right through to very large (easily seen with the naked eye).
Every individual tapeworm segment is essentially an individual egg-producing reproductive factory. Tapeworms are hermaphrodites (bearing both male and female sex structures). Each proglottid segment has its owntesticular-type organ structure/s and its own uterine organ structure/s (for creating and maturing eggs)and every single proglottid is, therefore, capable of producing and fertilising its own set of eggs, once mature. The small-sized proglottids nearest the anchoring 'head' of the Taenia tapeworm are the most under-developed and immature of all the tapeworm's segments and are, consequently, incapable of creating fertile eggs because of their under-developed state. The large proglottids nearest the 'tail-end' of the Taenia tapeworm are the most mature of all the tapeworm's segments and are capable of having their eggs fertilized and matured into an embryo-bearing state.
Author's note: because each individual proglottid segment can reproduce sexually on its own, some texts have described tapeworms as being almost like a colony (a large 'super-organism' made up of many individuals: each capableof living and reproducing without much assistance from the whole). Unlike a true colony, however, the individual reproductive segments of a tapeworm can not exist completely independently as individual units away from the whole. The individual tapeworm segments all rely on the survival and intestinal-attachment of the tapeworm's head if they are to remain within the definitive host animal and survive. Also, there is but one nervous system, under the control of the tapeworm head, linking all of the proglottids together in the tapeworm chain (i.e. the individual proglottid reproductive units are not so independent that they have been given their own individual nervous systems and brains).
Author's note: Because every individual proglottid contains both male and female sex organs, it is possible for a single proglottid to 'self-fertilise' (self-inseminate its own eggs). And thiscertainly does occur. In reality, however, it is probably much more common for individual proglottids to 'cross-fertilise' - inseminating other, nearby proglottids on the same tapeworm 'chain' and/or even proglottids located on completely separate tapeworms (i.e. other mature Taenia tapeworms that just happen to be living within reach). This makes for a better spread of tapeworm genes and lessens the degree of in-breeding.
When a proglottid enlarges and develops to a certain stage, becoming sexually mature, gametes (essentially sperm) from the male testicular components of the proglottidsegment fertilize the eggs (female) present within that or a nearby proglottid segment (as mentioned before, there can be cross-fertilisation from proglottid to proglottid). The newly fertilized tapeworm eggs matureinside of the proglottid, developing embryos inside of them, and the proglottid continues to grow in size. A proglottid that contains fertilized eggs inside is said to be "gravid" (i.e. a gravid proglottid).
Once the fertilised tapeworm eggs are fully-matured (ready to enter the next stage of the Taenia tapeworm life cycle), the now-enlarged, fat proglottid segment bearing them breaks away from the main body of the tapeworm.This proglottid segment exits the definitive host animal's body intact via the anus. The segment either physicallycrawls from the anus of the host animal by contracting its muscles and creeping along (people spotting these crawlingproglottid segments often think that their pet is infested with fly maggots) or it is voided in the animal's stools as the pet defecates. Sometimes a large section of the Taeniatapeworm (several proglottids in length) breaks away and is voided in the feces. These longer sectionsare almost invariably found by pet owners, sometimes causing alarm, particularly if the pet toilets ina litter tray that the owner has to clean.
Once out in the environment, the shed proglottid segment continues to writhe, breaking apart and expelling its fertilized, matured tapeworm eggs into the environment as it does so. Taeniids lacka pore for the eggs to come out of and so the proglottid needs to physically split open to release them.The eggs of Taenia tapeworm species are expelled from the proglottid segment as individuals.Each egg is infective the moment it exits the proglottid and generally contains an embryo (called a hexacanth) that has the potential to develop into an adult Taenia tapeworm at some point in the future (all going to plan with regard to the life cycle requirements of that individual Taenia species, of course).
The Juvenile Tapeworms Enter and Occupy the Intermediate Host:
An intermediate host animal that is specifically suited to the particular species of Taenia tapeworm in question (usually a livestock animal, such as a sheep, pig or cow, or a wild animal species, such as a wild ungulate, rabbit or rodent) consumes the Taeniid tapeworm eggs that have been shed into the environment.
These tapeworm eggs are typically consumed in a pasture or forest-type environmental setting. The infested definitive host animal defecatesonto the pasture (e.g. pasture on a farm) or in the forest (e.g. bushland, national park setting) and, in doingso, sheds infective tapeworm eggs into this environment. The organic fecal matter breaks down in days, but the resistanttapeworm eggs remain in the environment, speckled invisibly across the grass. The intermediate host animalconsumes the tapeworm eggs, thereby becoming infested, by eating the contaminated pasture contained within this forest orfarmland setting. On some occasions, an intermediate host animal may even consume an entire, freshly-shed, gravidproglottid (e.g. through the ingestion of fresh definitive host feces - which cows and pigs apparently like to snack on), resulting in the uptake of hundreds of eggs all at once by that intermediate host.
Aside from pasture contamination, tapeworm eggs (termed oncospheres) can also find their way into intermediate host animals via the contamination of waterways with tapeworm-infected feces (the intermediate host animal drinks the contaminated water and ingests the tapeworm eggs). Crops, vegetables and fruits fertilised with untreated sewage oreffluent (e.g. human effluent, animal effluent) can also become diffusely contaminated with tapewormeggs, which can then make their way into intermediate host animals through the consumption of these crops.Finally, insects (e.g. flies) and rodents can transfer the tapeworm eggs to the intermediate host via their feet(e.g. a fly lands on tapeworm-infected poo, picks up tapeworm eggs on its feet and then flies to the food of the intermediate host where its walking transfers the eggs onto the intermediate host's meal).
Author's note: You will notice that man is also listed on the above diagram as an intermediatehost for the Taenia species: Taenia solium (pork tapeworm). Humans infested with adult Taenia solium tapeworms can ingest their own tapeworm eggs or pass them on to other unwitting people, if they do not exercise good hygiene after using the bathroom (i.e. good hand-washing). Poor hygiene, resultingin the consumption of microscopic amounts of egg-contaminated human feces, can result in humansbecoming the intermediate hosts of the pork tapeworm (in place of the usual intermediate host, which isthe pig). This is very dangerous for the human who gets infested in such a way, as theintermediate tapeworm forms (termed cysticerci) can invade important internal organs like the lungs and brain,resulting in disease, disability and even death.
When the intermediate host animal consumes the tapeworm egg/s, the tapeworm embryos contained inside of these eggs survive and hatch from their eggs within the intestines of the intermediate host animal. The tapeworm embryos (termed hexacanths, but also called first stage larvae) migrate acrossthe intestinal wall and establish themselves within the organs of the intermediate host animal. Organs chosen for this larval invasion vary depending on the Taenia species involved.Some species of Taenia larvae invade only a limited range of tissues. For example, Taenia saginata and Taenia ovis favour muscle tissues, including the heart. Taenia taeniaeformis invades the liver. Other species of Taenia invade a muchbroader range of organs (making them very dangerous to the host). For example, Taenia solium larvaewill preferentially invade the liver, lungs, brain and muscle, but any part of the host body can, theoretically, be infested (e.g. bone marrow, mesentery, eye). This is what makes Taenia solium such a dangerous, life-threatening parasite for the intermediate host.
Once established in a chosen site, the Taenia tapeworm hexacanths (first stage larvae) develop and enlarge further into an intermediate larval tapeworm stage called a tapeworm cyst (termed a second stage larvae), the form of which (cysticercus, strobilocercus or coenurus - see diagrams and explanations below) depends on the Taenia species involved. From now on, when I mention cystic, juvenile or larval tapeworms present in intermediate host body tissues, assume I am talking about the stage two larval form of the Taeniid parasite.The speed of development of the second stage larval form is variable between the different Taenia species. Taenia saginata takes about 2 months for the invading hexacanth (stage 1 larva) to transform into a cysticercus (stage 2 larva).
Note on terminology: an intermediate host animal (e.g. sheep, cow, rabbit and so on) is a hostanimal that the respective Taenia tapeworm parasite needs to infest if it is to be able to complete an essential part of its lifecycle. In this case, the Taenia tapeworm needs to infest an animal host (generally a herbivore or omnivore) if it is to hatch from the tapeworm egg and transform into a second stage larval cyst. The parasitic tape worm is unable to reach adulthood and sexual maturity inside of the intermediate host animal and needs to later enter the body of a definitive host animal like a dog, cat or person in orderto achieve sexual and reproductive maturity.
The larval tapeworm cyst of most Taenia species takes on the form of a spherical, expanding, fluid-filled, bladder-like structure with a thin, almost-see-through, outer wall (at surgery or post-mortem evaluation, Taenia cysts look a bit like small, white-to-transparent water-balloons). The cysts are usually found imbedded in the tissues and organs of the intermediate host animal. The cysts are typically small (a few centimetres in diameter), but occasionallyTaenia cysts will be found that are quite large (around 10-20cm or more) in size. The size of the cystdepends on the species of the Taenia tapeworm (e.g. T. saginata cysts are usually small - about 10mm diameter); the length of time it has been present in the host's tissues (larger sizes may be attained with more time) and the structural form of the cyst (cysticercus, strobilocercus or coenurus - see diagrams below). On the diagrams below - the wall of the cyst or 'bladder' is colored pale blue and the fluid center is coloured in pink.
The inner lining of the cyst or 'bladder' is called a "germinal lining". It activelygenerates within the cystic confines one (e.g. cysticercus or strobilocercus forms) or more (e.g. coenurus forms) miniature larval tapeworm head/s (these tapeworm heads are termed 'scolices or protoscolices). These tiny tapeworm 'heads' (labeled as scolices on the diagrams below) are the individuals that become the adult tapeworms when the Taeniid cyst is later consumed by the definitive host animal (dog, cat, man). They have most of the physical structures that are present on an adult tapeworm head, including suckers ('acetabulums')and a hooked attachment structure called a 'rostellum' (note - some species of adult Taenia lack a rostellum so their juvenile forms won't bear this structure either).
There are three main structural forms that a Taeniid cyst can exhibit, with each species of Taenia tapeworm taking on just one of the three forms. A Taenia species will have only one form of intermediate host cyst - it will not alternate between the different types of larval cyst within that one species.
The first larval cyst form is the cysticercus (image 1, below). It is basically a bladder-like cystic structure with a single scolice contained inside. A single tapeworm egg ingested by the intermediate host animal will result in the formation of a single cyst containing a single scolice within the intermediate host (i.e. one scolice that is infective to the definitive host animal and which will result in the formation of one adult tapeworm). Taeniasaginata, Taenia solium, Taenia hydatigena, Taenia pisiformis, Taenia crassiceps, Taenia hydatigena and Taenia ovis all use cysticercus forms of juvenile tapeworm cyst and the infestationof the intermediate host, when it occurs, is termed: cysticercosis.
The second larval cyst form is the strobilocercus (image 2, below). Similar to the cysticercus, the strobilocercus is basically a bladder-like cystic structure with a single scolice. Unlike the cysticercus, the scolice of the strobilocercus seems to be more well-developed, containing a goodlength of body (strobila) behind the head or 'scolex' structure. As with the cysticercus, a single tapeworm egg ingested by the intermediate host animal will result in the formation of a single scolice within the intermediate host (i.e. one scolice that is infective to the definitive host animal and which will result in the formation of one adult tapeworm). Taeniataeniaeformis uses a strobilocercus form of juvenile tapeworm cyst.
The third larval cyst form is the coenurus (image 3, below). Similar to the cysticercus, the coenurus is basically just an expanding, bladder-like cystic structure, except that it contains numerous scolices, not just one. With the coenurus, a single tapeworm egg ingested by the intermediate host animal will result in the formation of a single cyst containingmultiple scolices within the intermediate host animal (i.e. many scolices that are infective to the definitive host animal and which will result in the formation of several adult tapeworms uponconsumption by the definitive host animal). Taenia multiceps, Taenia serialis and Taenia brauni use a coenurus form of juvenile tapeworm cyst.
Taenia tapeworm life cycles image - Cysticercus form of juvenile tapeworm cyst.
Taenia tapeworm life cycles diagram - Strobilocercus form of juvenile tapeworm cyst. This strobilocercus has been drawn 'evaginated' (with its head and neck poking outside of the fluid-filled bladder structure). Typicallythis evagination only occurs once the strobilocercus is eaten by a definitive host animal (the cystic 'bladder'then digests away, leaving the head and neck behind to attach to the definitive host's intestinal wall). When it is located within the tissues of the intermediate host, the strobilocercus is generally 'invaginated'with its head and neck hidden within the fluid-filled cystic bladder structure. Thus it really should have been drawn morelike the cysticercus (picture 1), just with a longer neck region.
Taenia tapeworm life cycles picture - Coenurus form of juvenile tapeworm cyst.
Side note - the cysticercus form of Taenia crassiceps is capable of budding. A singlecysticercus of this species can bud off replicas of itself, each containing an infective scolice. This increases the amount of regional tissue damage caused by the tapeworm larvae and resultsin the formation of several adult tapeworms within the definitive host, should the definitive host happen toconsume all of the cysts in the budded cluster. The condition can mimic hydatid disease, but shouldbe differentiated from this, much nastier, condition.
The Taenia cyst can cause damage to the intermediate host animal's tissues as it grows.The damage is generally in the form of pressure atrophy - the cyst crushes the tissue cells around it as it expandsin size, causing the cells of the infested organ to die off bit by bit. Sometimes the cystcrushes a vital blood supply, killing the cells and organs supplied by that circulatory pathway. Sometimesthe cyst crushes other vital tubular structures like the gall bladder, ureter, bile ductand bronchi, causing severe dysfunction of these conduits. Sometimes the cyst can leak small amountsof fluid into the surrounding tissues, resulting in severe allergic reactions (the host immunesystem attacking the fluid) and painful tissue inflammation of the area. Such aggressive inflammation (e.g. immune cells releasing chemicals that destroy and damage protein and cell structures) canbadly injure the surrounding host tissues, even though the main aim of the attack was to destroy the foreign cyst-fluid and 'save' the host tissues. Should a largecyst happen to rupture, the massive fluid release can result in a severe anaphylactic reaction(the sudden death of the patient is quite possible should this occur).
The symptoms and consequences of this damage depends very much on the size and number of the Taeniid cystspresent and on the organ location that the cysts have invaded. Because most organs(not the brain) have a high degree of tissue redundancy (meaning that a lot of tissue can be lost beforesymptoms of organ damage present), a quite-sizeable population of small Taenia cysts may not produce any obvious symptoms in the intermediate host for a long time. The liver is a good example of this - many small Taenia cysts in the liver may not cause any signs of ill-health(unless they happen to be positioned such that they squash a vital liver structure like the gall bladderor common biliary duct). Lung cysts may also present initially with minimal signs,however, the animal will generally develop coughing, shortness of breath, pneumonias and wheezingas the cyst/s expand. On the flip side, certain other organs can not tolerate even the smallest of tapeworm cystswithout showing side effects. The brain is a classic example of this - even a very small cyst in the braincan result in severe neurological deficits within the infested host. This is why Taenia soliumand Taenia multiceps (both of whom love to invade the brain) can be so dangerous to their intermediatehost animals.
Images of Taenia cysts in organs:
http://www.cfsph.iastate.edu/DiseaseInfo/ImageDB/TAE/TAE_001.jpg - Taenia solium cysts in pig muscle (pork).
http://images.medscape.com/pi/features/slideshow-slide/neurocysticercosis/fig1.jpg - Taenia solium cysts in a human brain.
http://cal.vet.upenn.edu/projects/paraav/images/lab7-16.jpg - hundreds of Taenia saginata cysts in a cow heart.
http://www.aans.org/bulletin/images/Vol17_3_08/OcularCysticercosis_small.jpg - Taenia solium cyst in a human eye.
The Definitive Host Becomes Infested With Adult Taenia By Consuming the Intermediate Host:
The definitive host animal (dog, cat, human) becomes infested with the adult tapeworm form of the Taenia tapeworm life cycle by consuming the larval-cyst-infested organs of an intermediate host animal that has become infested with the 'right' Taenia species for thatdefinitive host animal. This host-specificity is quite important. The right Taenia species must be ingestedby the right host if an adult tapeworm is to result. A cow infested with Taenia saginata cystscould be eaten by a dog or a cat without either of those two animals getting the adult tapeworm.This is because the adult T. saginata tapeworm only develops in the intestines of a human being. In the dog or cat, the T. saginata tapeworm cyst will simply be digested and not turn into an adult worm.Likewise, a human who ingests the undercooked meat of a sheep will not get Taenia ovisbecause Taenia ovis requires a canine host to achieve adulthood. And so on.
The definitive host animal must eat an infective, fertile cyst, containing activeprotoscolices, if it is to become infested with the adult Taeniid tapeworm forms.This sort of consumption is common in the animal world, where cats and dogs, both wild and domestic, feast on the fresh, warm offal of their freshly killed prey (e.g. rabbits, rats, mice, voles, sheep). It can also occur in the domestic domain, when farmers offer the raw innards or body parts of freshly-killed livestock and rabbits to their dogs and cats or hunters allow their pets to snack on the results of their shooting trips (e.g. pig and deer hunters often feed their dogs on the raw meat and organs of the animals that they have killed). In the kitchen, it is manwho is at risk of becoming infested. The consumption of undercooked meat, particularly pork and beef, can result in the human diner gaining an unwanted parasitic guest.
When the definitive host animal consumes the tapeworm-cyst-infested intermediate host tissues, the mini-tapewormprotoscolices (which up until now have been 'invaginated' - held inverted inside of their cystic bladder support structures) evaginate and poke out of their bladder support structures. The supportive bladder-like structuresdigest away and only the head and neck of the protoscolice is left, floating freely within the small intestinaltract of the definitive host carnivore. These protoscolices will develop into final-stage adult tapeworms. They will attachto the wall of the host's intestinal tract and begin feeding and budding off proglottid segments. Eventually mature proglottids will develop, be fertilised and become egg-laden. Egg-containing proglottids will eventually start shedding out into the droppings.
The first adult tapeworm eggs will start appearing in the definitive host animal's environment about 6-8 weeks after the Taenia-cyst-infested intermediate host animal was first ingested. Adult wormscan live in the definitive host animal for a period of 6 months to almost 3 years, but some species are known (e.g.T. saginata of man) whose adults can live for around 20 years in a single host.
Thus the Taenia tapeworm life cycles continue ...
Author's note: The Taenia tapeworm life cycle tends to be most successful and prevalentwhen the 'right' definitive hosts and intermediate hosts for that species of Taenia live and feed in close proximity to one another (which makes obvious sense). Strong tapeworm life cycles tend to establish in environments between animals that have a natural host-prey relationship. For example, a tapeworm life cycle commonly exists in areas where cats and rodents co-exist. The infested cat defecates Taenia taeniaeformis tapeworm eggs onto the grass, infesting the local herbivorous rodent populationwith hepatic strobilocercus cysts that are later consumed by the cat whenit hunts and consumes the rodents. Similar problems occur on farms when tapeworm-infested dogsare allowed to defecate onto the grasslands and pastures of sheep and cattle. These livestockanimals become infested with cysts, which the dog might later get to consume if it comesacross the carcass of an animal that has died as a result of its parasitism.
It is for this reason - the ability to maintain a strong definitive-host and intermediate-hostrelationship (essential to tapeworm life cycles) - that the majority of domestic animalTaeniid infestations occur in dogs and cats that come from or have regular access to rural regions (livestock and rabbits),grain-stores (mice and rats), farms and wild spaces (e.g. national parks with lots of wild animal intermediate hosts).Dogs and cats that spend lots of time in these environments, hunting their own prey and feeding on offal and carcasses (e.g. working dogs, herding dogs, hunting dogs, pig-dogs) are at greater risk of carrying and passing on Taeniid tapeworms.
Prevention of tapeworm cysticercosis and coenurosis in sheep and cattle really requires that infecteddogs and canids not be allowed access onto animal pastures. This is often hard to enforce so farmers lookingto prevent their livestock from becoming spoiled by tapeworms should deworm all their dogs regularly, avoid feedingthem raw offal and meat and put up suitable fences to avoid having potentially-infested wild canids poopinginto the pasture.
2) Taenia tapeworm symptoms and outcomes - the significance of Taenia infestations in intermediate and definitive host animals.
The following two sections contain information on the significance of Taenia tapeworm infestationsin both definitive host and intermediate host animal species. I have elected to discussthe significance of these tapeworm parasites for both types of hosts because, even though this is primarily asmall animal veterinary website, the impact of the parasites on the intermediatehost animals is highly significant (often life-threatening) and an integral reason as to why there is a need for the prevention of tapeworm parasites in the definitive host animals (we do not just prevent tapeworms in dogs and cats for their well-being but for the well-being of livestock animals and other intermediate hosts also, whose very lives could be lost should they contract the tapeworm cysts from the egg-laden feces of infested dogs and cats).
When we talk about tapeworm infestations, most people only picture the adult tapeworm infestation of the intestinaltract of the definitive host animal or human. What many people fail to realise, however, isthat most adult tapeworm infestations of dogs, cats and people typically produce little discomfort or evidence of disease (unless the worms are large in size; large in number or the host is health-compromisedin some other way) and are of little clinical significance to the carrier (the obvious exception being the nasty Taenia solium pork tapeworm, which poses a dangerous cysticercosis risk to the human carrier if it remains undiagnosed and untreated).
In fact, most of the big disease problems seen with Taenia tapeworm infestations actually occur in the intermediate host animals: the result of internal organ infestation with thejuvenile cystic forms of the tapeworm life cycle. Numerous, expanding cysts in importantbodily organs can be devastating for the intermediate host animal, often resulting in significant symptoms of disease and disability. From an animal production viewpoint, Taenia cysts in the meat and organs of livestock animals (e.g. pork and cattlein particular) can also be devastating, as such infested meat is often down-graded or outright rejected for sale. In the case of pork, meat infested with Taenia solium cystsis outright dangerous for the consumer, should unprocessed, raw pork enter the human food chain.
2a) Taeniid tapeworm symptoms and significance in intermediate host animals.
1) Disease significance:
The disease significance of Taenia tapeworms is very much dependent upon the species ofTaenia we are talking about and, in particular, which body tissues the juvenile tapewormcysts tend to localise in.
Some types of larval Taenia cyst (e.g. Taenia pisiformis cysticerci of rabbits)localise within the abdominal spaces of their intermediate host (i.e. in the fat and connective tissues surrounding the abdominal organs), where they have plenty of room to expand and grow without impacting on the organs. In such cases, no symptoms may be appreciated by the infested animal or its owner (if one exists).
Other types of Taenia (e.g. Taenia taeniaeformis, Taenia hydatigena, Taenia solium) have a trophismfor the liver. Being a highly redundant organ (i.e. meaning that lots of tissue can be lost from the liver before symptomsof liver disease will occur), small numbers of slowly expanding cysts may not produce anysymptoms of hepatic disease in the animal for a long time. In larger numbers and sizes, however, liver dysfunctioncan eventuate, resulting in wasting, thinning, jaundice, 'fluid-belly' (ascites) and general unwellness of the animal before death. Alternatively, a small number of cysts located in particularly 'bad' regions of the liver (e.g such that they compress the biliary ducts or major blood vessels) could result in significantsymptoms of disease (e.g. biliary obstruction) even though only a small number of cysts is presentand most of the liver tissue is healthy.
Side note - if a massive number of tapeworm eggs is eaten all at once, the huge influx of embryonictapeworms into the animal's liver can cause very severe injury to the liver, resulting in acutehepatitis and death. At this point, no second-stage larval cysts will yet have formed - it will be the migratingfirst-stage larvae (the hexacanths) doing all the damage.
Various other species of Taenia (Taenia solium, Taenia saginata, Taenia ovis, Taenia serialis)are attracted to the muscles of the intermediate host animal, including the heart muscle. In low to medium numbers, these cysts will usually cause no symptoms in the infested animal, unless they are located within the heart where even small populations can result in sudden death. In large numbers, such cystsmight be expected to cause pain in the affected muscles, something that the ownermight recognise as lameness or stiffness of the gait. It is worth noting that, aside from the diseasesignificance, the presence of larval cysts in the muscles and meat of affected cattle and pigshas significant financial ramifications for the affected farm, as such meat is generally rejectedfor commercial sale and may pose a serious risk to human health (T. solium).
Taenia multiceps, as an individual Taeniid species, poses a severe health threat to sheep (occasionally humansand other animals) who contract it because it tends to localise in the brain. Even a single, expanding cyst can produce severe signs of neurological dysfunction (brain damage) and even death in the sheep infested with it. The disease in sheep is nick-named 'gid' because it often makes the sheep wobbly and uncoordinated when it walks (i.e. 'giddy'). Other signs of the condition also include: paralysis, head-pressing, star-gazing, circling, seizures and death. It is a terrible condition for the sheep intermediate host, yetthe dog definitive host will tend to show little sign of infestation itself. Taenia solium issimilarly dangerous because it will also often invade the brain of the intermediate host that it infests (pig, human).
Some species of Taenia (e.g. Taenia solium) are less selective about wheretheir cysts localise, making them extremely dangerous for the animal (pig or human)that contracts them. They produce major disease concerns when their expanding, space-occupying cysticercuslarval cysts turn up in the vital organs (e.g. brain, liver, lung, kidney, eye) of intermediate host animals (pigs) and, most worryingly, people. The cysts grow and expand, crowding out and compressing the cells thatmake up the organs they have invaded. This eventually leads to the dysfunction of these internal organsas vital structures get compressed (e.g. blood vessels that supply nutrients and life to organs may be closed off; drainage structures like biliary ducts and ureters, which help to draw fluid from various organs, may be compressedshut; airways that provide oxygen to the lungs may become squashed by the enlarging cysts and so on) and even destroyed (e.g. compression of organ cells by an expanding cystic mass can result in their death from compression injury - termed "pressure atrophy"). If not diagnosed and treated promptly, the cyst-induced organ damage (e.g. brain damage, lung damage) can become so severe that the animal orperson with the Taeniid disease will become permanently compromised or even die.
Humans with Taenia solium of the brain can show a range of neurological signs including: fever, chronic head-ache, irritability, blindness, dementia, seizures, focal lesions, incoordination, wobbliness, confusion, paralysis and personality changes. Somepeople present with signs of stroke and others can present with sudden death.
Allergic and anaphylactic reactions are also possible when large larval cysts are present within the bodyof a human or animal. Some larval cysts will leak small amountsof protein-rich fluid into the surrounding host tissues, resulting in allergic reactions atthe site of the leakage (the host immune system attacking the fluid) and painful tissue inflammation of the area. Low-grade inflammation can present vaguely as signs of fever, rash, night-sweats and increased lymph node size. More aggressive inflammation (e.g. immune cells massively releasing chemicals that are designed to target and destroy protein structures and 'foreign substances') can badly injure the surrounding host tissues, even though the sole aim of the immune attack was just to destroy the foreign cyst and its oozing fluid. Should a largecyst happen to rupture, the massive fluid release can result in a severe anaphylactic reaction(the sudden death of the patient is quite possible should this occur).
Another risk posed to all animal intermediate hosts by Taenia, regardless ofspecies and organ distribution, is septic peritonitis. When Taenia eggs are consumedby the intermediate host animal, the embryonic tapeworms (hexacanths) need to penetrate through the gut wall of theanimal if they are to enter the internal organs. A penetrating embryo can draw intestinal bacteriathrough the gut wall with it, resulting in severe, life-threatening bacterial infection within the abdominal cavity of the animal. Some of these bacteria(especially Clostridial forms) can be extremely nasty, resulting in septicaemiaand death within hours to days of infection.
It is possible for larval cysts to undergo weird mutations within the tissues of the intermediate host animal. Should the wrong cellular mutations occur, the cysts can start to grow rapidly in bizarre, atypicalways, aggressively invading the host's tissues and organs and acting like a cancer. Such a mutated,malignant larval structure of non-host-tissue-origin is termed a teratoma. Surgery to remove the organismis the only way to save the host (provided the condition is not too advanced) and, in many cases, the surgeon will find it difficult to determine exactly what the teratomatous object in question is, it isso far removed from its normal, round, cystic appearance.
The risk of immune system compromise and subsequent death from other unrelated disease causes also goes up for animals severely infested with Taenia cysts. Even though the cystic infestations may not be bad enough to cause deathoutright (certainly not rapidly, in any case), significant larval cyst burdens can result in the animal's appetite being reduced and its energy expenditure being increased (energy lost throughimmune attacks on the cystic 'foreign bodies' and general inflammatory processes) - a situation that results in the overall thinning, ill-thrift and ill-health of the affected animal. Such unwellanimals are liable to having a degree of immune system compromise, meaning they are more prone to dying from common infections and parasites that, before, would not have bothered them.
Animals that show ill-thrift, thinning and general weakness (as per above paragraph) are liable tobeing predated upon by domestic and wild animal predators. For example, a thin, skinny, weakrabbit infested with a large T. serialis burden is more at risk of being eaten by a hawkor a cat.
2) Commercial significance:
From a livestock production point of view, the financial losses to commercial meat producers can alsobe significant. Meat and offal infested with Taenia cysts of any species (even thosespecies not infective to man) will most likely be rejected from the commercial food chain (i.e. won't be able to be sold) because people won't buy it (people are unlikely toeat meat or organs with cysts in them).
Should Taenia saginata cysts be found in beef (meat), the meat rejection is likely to bedoubly-enforced since the organism is of significance to human health.
Should Taenia solium cysts crop up in pork, the negative reaction is likely to be even greater. Thatthe meat in question will be rejected is obvious, however, the consequences for the infected farm maybe even greater than this. Taenia solium is known to be highly dangerous to man andit is considered exotic and notifiable in many countries. A farm that tests positive to this organismmay well find itself under strict quarantine with an investigation underway as to where theinfection came from (other farms might also become implicated and many livestock may be destroyedas a result).
Obviously, any deaths that occur as a result of infestation with any of the Taenia species (e.g. Taenia multiceps in the brain of a sheep, Taenia ovis entering the heart)count as commercial losses. A dead animal produces no meat, wool or milk and is a financialloss. Should that deceased animal be of genetic value (e.g. a good stud bull, a high-yield dairy cow), then thecommercial loss is compounded through the loss of those 'productive' genes to future generations of animals.Extra cost will also be incurred in replacing the valuable animal.
Additionally, the overall loss of stock productivity that can occur as a result of even moderateinfestations with Taenia cysts should not be forgotten. Even though cyst infestations may not be enough to cause deathoutright (certainly not rapidly, in any case), significant larval cyst burdens can result in the animal's appetite being reduced and its energy expenditure (energy lost throughimmune attacks on the cystic 'foreign bodies' and general inflammatory processes) being increased - a situation that results in overall thinning, ill-thrift and ill-health of the affected animal. Such animals are likely to have less meat (meat that might notbe saleable anyway) and reduced outputs of both milk and wool of any quality. All of this representsa commercial loss.
3) Zoonotic and human health significance:
Taenia saginata (beef tapeworm) is of some zoonotic significance to human beings. Humanswho eat undercooked beef (especially 'blue' or tartare-style raw meat) may ingest larval cysts of this Taenia species. When it grows in the human gut, the adult form of this worm can attainlengths of many metres - a size that might produce symptoms of nausea and discomfort(see section 2b on definitive host signs) and weight-loss in the human infected with it.
Taenia solium (pork tapeworm) is of huge zoonotic significance to human beings.Similar to the situation seen with Taenia saginata, humans who eat undercooked pork may ingest larval cysts of this Taenia species. When it grows in the human gut, the adult form of this worm can attaina good size - potentially producing symptoms of nausea and discomfort(see section 2b on definitive host signs) and weight-loss in the human infected with it. Of infinitelymore significance, however, is the fact that a human infested with adult Taenia solium can go on to self-infect his/her internal organs with nasty Taenia solium cysts, through even the slightest lapses in personal hygiene. This can result in the eventual death of the person so-infested.
2b) Taeniid tapeworm symptoms and significance in definitive host animals.
Adult Taenia parasites located in the intestinal tracts of animals and people can pose a variety of problems for pets (dogs and cats) and humans including:
- non-specific intestinal disturbances - tapeworms can produce some non-specific signs of intestinal discomfort and pain (e.g. colic signs) in animals and humans. Tapeworm afflicted humans often complain of cramping and nausea: signs that are generally difficult to ascribe to animals, but which probably do occur in them also (animals can't actually describe such vague feelings of cramping or nausea to us humans - so we are generally unaware of these signs in them). Vomiting may also result.
- non-specific appetite changes - tapeworms can cause some animals and people to go off their food or to become fussy or picky about their eating habits (this appetite loss is possibly the result of such factors as abdominal pain and nausea - described above). In contrast, certain other individuals develop a ravenous appetite in the face of heavy tapeworm infestations because they are competing with the parasite/s for nutrients (they need to physically eat more to provide enough nutrition for both themselves and the worms).
- non-specific fever - tapeworms can be associated with recurrent fevers.
- body weakness, headaches, dizziness, irritability and delirium - sometimes described in human tapeworm infestations, non-specific signs of weakness, headache and dizziness may occur in animals also. Whether we would ever actually be likely to diagnose these sorts of non-specific signs in our pets is the real question, however - if our pets can not actually describe sensations of dizziness or headache to us humans, then how would we ever know? It certainly is a sign described in human tapeworm conditions, however.
- malnutrition - very large numbers of adult Taenia tapeworms present in the intestinal tracts of dogs and cats (particularly small puppies and kittens) can result in the malabsorption of nutrients (food) by the infested animal. This can cause the tapeworm-parasitised animal to not receive the nutrition it needs (i.e. to not absorb its food properly), resulting in malnourishment, weight loss, ill-thrift and poor growth. It is possible that malnutrition may also occur in humans who have heavy tapeworm burdens, although this finding would be expected to be less commonly seen in humans than in animals.
- poor coat and hair quality - severe malnutrition and malabsorption of vitamins, minerals and proteins can result in reduced quality of the haircoat - e.g. brittleness, thinning, coarseness and loss of lustre of the coat.
- intestinal irritation and diarrhea - when an adult tapeworm inhabits the small intestine of an animal or human, it finds a suitable site along the lining of the intestinal lumen and grasps on to it using suckers (acetabula) and a spiny anchor-like organ called a rostellum. This spiky tapeworm grip is irritating to the wall of the small intestine, creating discomfort for the host and alterations in intestinal motility and regional intestinal mucus secretions, which can result in diarrhea (note that diarrhea is mainly seen only in very heavy tapeworm infestations). In some individuals, the penetrating rostellum causes a severe inflammatory, allergic reaction within the host's intestine (the host's immune system actively rejects and attacks the tapeworm proteins), causing the animal host to exhibit abdominal pain and diarrhea. Note that T. saginata, sometimes called the 'unarmed tapeworm', lacks a spiny rostellum so is not quite so damaging to the human intestine.
- intestinal blockage - it is possible for massive tapeworm infestations to block up the intestines of animals (especially small puppies and kittens) and children, producing signs of intestinal obstruction (e.g. vomiting, shock and even death). This is not common, but it can occur if worm burdens are large and/or if someone deworms the infested animal, killing all of the worms in one hit (the tapeworms all die and let go of their intestinal attachments at the same time, resulting in a vast mass of deceased tapeworms flowing down the intestinal tract all at once and causing blockage).
- intestinal perforation - rarely, some adult Taeniids (e.g. Taenia saginata beef tapeworms) can perforate the intestinal wall, ending up inside of the host's abdominal cavity. This can result in life-threatening abdominal inflammation and infection and septicaemia.
- appendicitis, biliary obstruction, pancreatitis - rarely, some adult Taeniids (e.g. Taenia saginata beef tapeworms) can migrate up into the duct systems of the pancreas and biliary tract (bile duct), producing blockages and painful inflammation of these regions. Some may even enter the appendix and cecum, causing nasty inflammation of these regions (termed appendicitis and typhlitis respectively). This can result in life-threatening complications that may require surgical correction.
- perineal or anal irritation and scooting - the migration of tapeworm segments from the anuses of infested dogs and cats can result in itching and irritation of the anus. The dog or cat will respond by excessively licking the anus in order to remove the irritation or, if it can not reach, it will drag and rub its bottom on the ground to remove the irritation. This bottom rubbing, called "scooting", is usually a sign of anal or perineal irritation and evacuating tapeworms can be one cause of this (side note - anal gland impaction or infection is a much more common cause of scooting, however, it can be a sign seen in 'wormy' animals). Note that anal irritation can be experienced by people infested with tapeworms, resulting in 'bottom scratching' (typically pin worms cause most cases of anal irritation in people, not tapeworms).
- annoyance - most pet owners don't like to see or hear their pets fastidiously licking their bottoms or rubbing their butts along the carpet. This annoyance is compounded when the rubbing activities result in fecal staining of floors or if tapeworm segments are actually seen extruding from the animal's anus;
- gross-out factor - the sight of long tapeworms in the feces and/or white, grub-like tapeworm segments crawling from a pet's anus is revolting and off-putting to many people who see such infestations as a sign of 'dirtiness' and 'disease' (even though clean pets can and do get tapeworms of course). The disgust and horror is likely to be compounded if the tapeworm in question is actually coming out of you!
- zoonosis (human infestation) - Adult Taenia solium tapeworms produce eggs that are infective to humans. Humans who inadvertently ingest fecal matter containing tapeworm eggs can develop life-threatening larval tapeworm infestations of the organs (including the brain) potentially resulting in death.
Of all of the problems mentioned above, the disgust factor (gross-out factor) is probably the mostsignificant and commonly seen in the vet clinic. Tapeworm-associated problems like malnutrition, intestinal irritation, perineal irritation, diarrhea, intestinal blockage and poor coat quality are seen of course and are greatly problematic for the host animal when they do occur, however, it must be stated that it generallyrequires a massive tapeworm burden to be present before such severe signs are likely to be encounteredin practice. As a vet in Australia, I have not personally seen an adult Taenia
tapeworm burden so massive as to result in a major malabsorption or intestinal disturbance issue (although under certain hygiene and living conditions, I do not doubt that it probably occurs). Far more commonly, people come to me in a panic because they have just found a large, white worm in the droppings of their cat or dog or seen a pale, fat, maggot-looking tapeworm segment slither out of the anus of their puppy. In these quite common situations, the animal in question is generally healthy and fine (it just needs worming treatment) - it's the owner who's the one needing the reassurance (and the smelling salts)!
3) Treatment and prevention of Taenia tapeworm infestations in animals.
Adult Taeniid tapeworms in dogs and cats (and people) can be eliminated from the animal's intestinesusing tapeworm-specific anti-cestodal medications like praziquantel or niclosamide. Of thetwo drugs, praziquantel is the anticestodal drug most commonly included in most commercially-availabledog and cat 'all-wormers' because it has good activity against another nasty tapeworm parasitecalled Echinococcus* (the hydatid tapeworm), which niclosamide does not. Detailed information on praziquantel is contained below. Passing mention is made about niclosamideand other lesser-used anticestodal drugs in the below section marked "Other Anti-Cestodal Drugs."
When an adequate dose of either anti-tapeworm drug is administered to the definitive host animal, the Taeniid tapeworms die and are voided in the host animal's feces (pet owners may find several large, dead tapewormsin their animal's feces following the administration of just such a wormer). This single treatment is usually curative, however, several doses may be needed to completely rid an animal of a very large tapewormburden (if a large tapeworm burden is suspected, the praziquantel can be repeated two-weekly for a couple of dosesto be sure of getting them all).
Author's note: Be aware that most deworming medications (aside from some heartworm meds) do not generally last very long in a treated-animal's system. When an all-wormer is given to a pet, the drugs work rapidly, killing off the adult worm parasites, before disappearing. The drugs do not hang around to protect the pet against subsequent tapeworm infestations. This means that shouldthe pet continue to eat larval-tapeworm-infested rodents, rabbits and livestock in the days followingthe deworming treatment, they will most likely become rapidly re-infested with adult tapeworms.
Following the ingestion of a cyst-infested intermediate host rodent, rabbit or livestock animal, a definitive hostdog or cat can have a reproductively-mature, proglottid-shedding adult tapeworm inside of itsintestine within a mere 6-8 weeks. In high-transmission situations (e.g. a dog fed frequently on raw offal, acat that hunts), this could mean that a pet owner might need to repeat worm (tapeworm-treat) his dog or cat every 6-8 weeks to keep the adult tapeworm numbers under control!
Because such frequent 6 weekly worming may not be practical for some pet owners (particularly ownersof hard-to-pill cats), the best option for the ongoing control of Taenia tapeworms is to:
a) give the animal regular tapeworming medications (as per the manufacturer's directions) and
b) not allow the animal access to foods likely to contain larval tapeworms (e.g. raw carcasses, raw offal, hunting).
* be aware that not all tapeworm-killing drugs kill thenasty Echinococcus hydatid tapeworm species, so do make sure you check that any tapeworm medication you give is appropriate for killing this particular tapeworm species. Hydatid tapeworms are not Taenia species and so do not really belong on this page, however, they are so dangerous that I do not want them to be forgotten during the discussions on Taenia treatment and prevention. (Praziquantelis a good choice for hydatid tapeworms and is easy to get. For other anti-tapeworm medication options,see the notes at the bottom of this section to see whether or not they kill Taenia and Echinococcus.)
Praziquantel is a powerful tapeworm-killing drug that is generally included in the vast majorityof commercially-available 'all-wormers' given to dogs and cats. It has a high margin of safety in dogs and cats(and many other species) and exhibits very good activity against most of the major tapeworm species affecting our domestic pets (including: the common flea tapeworm - Dipylidium caninum; the hydatidtapeworms - Echinococcus granulosus and E. multilocularis; the zipper worm - Spirometraand the many varieties of Taenia tapeworm species). It is because of this excellent activity against such a wide range of pet tapeworm parasites that praziquantel tends to be favored overniclosamide and most other drugs in the control of tapeworms in domestic household animals.
How it works:
Tapeworms are coated in protein molecules that shield them from being recognized and attacked bythe host animal's immune system. These protein molecules turn over and shed from the tapeworm's body surface (tegument)constantly. By the time the host's immune system recognises and starts to attack one lot of tapeworm surface molecules, these have been shed from the tapeworm's 'skin' (tegument), leaving the immune system with nothing recognisable to attack.
Praziquantel works by disrupting the surface tegument of the tapeworm such that the animal's immune system is capable of recognizing the tape worm as foreign and actively attacking it. Additionally, praziquantelalso works by massively increasing the influx of calcium ions into the tapeworm's body. This calcium overload causesthe worm's muscles to become over-stimulated such that the worm develops stiffness and rigidity. The rigidtapeworm is unable to maintain its hold on the host's gut wall and is, consequently, voided from the animal's intestinal tract via the faeces.
Features of praziquantel:
- The treatment of choice for adult tapeworms in dogs and cats. Can be used in people (do NOT be tempted to self-medicate with your pet's medications though - see a doctor if you require a tapeworm treatment).
- Kills a wide range of adult cestode (tapeworm) species in definitive host people and animals.
- Also kills some forms of trematode (fluke) parasite in livestock animals.
- In very high doses, praziquantel also kills certain intermediate-stage, larval tapeworm forms (including cystic larval forms of Taenia like T. solium). For example, praziquantel and albendazole were used together to treat a woman infested with the budding cysticerci of Taenia crassiceps (ref 9) to good effect.
- Very effective at killing adult Dipylidium caninum flea tapeworms, adult Taenia tapeworms, adult hydatid tapeworms and also many other important tapeworm types afflicting domestic animals.
- A dose of only 2mg/kg is needed to kill all adult Taenia types (some Taeniids only need 1mg/kg). Most all-wormers actually contain a dose of 5mg/kg praziquantel (a higher dose - needed for other tapeworm species), which is more than ample for killing this adult tapeworm Genus.
- A dose of 2.5-5mg/kg is needed to kill Dipylidium. Most all-wormers contain 5mg/kg praziquantel, which is ample for killing this flea tapeworm.
- A dose of 5-10mg/kg is needed to kill hydatid tapeworms (Echinococcus species) in dogs. The higher dose range is recommended to kill sub-adult forms of the worms in dogs. Most all-wormers contain 5mg/kg praziquantel, which is within the dose range for killing these nasty tapeworms, however, given how dangerous hydatid tapeworm infestations are to people, if I was a dog owner living in a high hydatid risk situation, I would probably err on the side of caution and give the higher dose (10mg/kg). For info on hydatid tapeworms, see our hydatid tapeworm page.
- Some tapeworms like Spirometra mansoides and Diphyllobothrium erinacei require an intermediate, high dose range (7.5mg/kg) be given on 2 consecutive days to clear them.
- Many of the tapeworms and flukes afflicting livestock animals need high doses of praziquantel if they are to be cleared (in the order of 15-30mg/kg and higher).
- Praziquantel, given orally, absorbs into the animal's body rapidly, reaching many organs including the liver and brain (this body-wide, systemic absorption is why praziquantel is effective against Schistosoma and certain larval tapeworm forms).
- Praziquantel has a wide safety margin and is difficult to overdose (dogs were tested on up to 180mg/kg orally with little side effect).
- Praziquantel is thought to be safe in pregnant and breeding animals (check with your vet to be sure though).
- Some praziquantel-containing products advise not using praziquantel in puppies or kittens under 4 weeks of age. Given that pups and kittens 3 weeks and below are only fed on milk, they do not really need a tapewormer anyway as tapeworms are only caught by eating intermediate host tissues.
- Second to niclosamide, praziquantel is a good option for treating Taenia saginata in people. It is often given to human patients in conjunction with niclosamide.
- A major choice for treating adult Taenia solium in people.
- Side note - Praziquantel also kills Schistosoma - an important parasite of humans, which causes a terrible, often fatal, liver condition called bilharzia (common in third world countries).
- Side note - Does not kill roundworms or hookworms or other nematode parasites. Praziquantel kills cestodes (tapeworms) and certain trematodes (flukes) only.
A related product called epsiprantel has been used to kill flea tapeworms and Taenia
in dogs and cats. I have never used the product personally and can not vouch for its efficacy or safety.
NOTE - Please read our disclaimer before attempting to self-diagnose and dose your animals withany drugs mentioned on these pages. Pet Informed is a general advice website only and mistakes can bemade - we always recommend that you double-check any of our information with your own vet.
Taenia tapeworm life cycle picture: These are photographs of the box-labels of a common dog and catall-wormer called Milbemax. You can see from the first image that the product contains praziquantel(25mg of praziquantel per tablet - underlined in aqua). The second image shows the range of parasites thatthe product kills. The flea tapeworm, Dipylidium caninum (underlined in orange), hydatid tapeworm (underlined in grass green)and Taenia tapeworm (underlined in red) are all listed as parasites that this product kills. Also mentioned on the Milbemax box was the minimum recommended dose rate of praziquantel (underlined in pink) - it is listed as 5mg/kg.
Taenia tapeworm life cycle picture: These are photographs of the bottle-labels of a common dog and catall-wormer called Fenpral. The first image is a picture of the product bottle (dog version of Fenpral). The second image shows that the product contains 50mg of praziquantel per tablet (blue arrow). The image shows the range of parasites thatthe product kills. The flea tapeworm, Dipylidium caninum (underlined in orange), hydatid tapeworm (underlined in grass green)and Taenia tapeworm (underlined in blue) are all listed as parasites that this product kills. Also mentioned on the Fenpral bottle is the minimum recommended dose rate of praziquantel (underlined in pink) - it is listed as being 1 tablet per 10kg ofbodyweight. Given that a single tablet contains 50mg of praziquantel, this must mean that theminimum dose rate for praziquantel is, again, 5mg/kg (i.e. a 10kg dog gets 50mg so a 1kg dog must get 5mg).
Other Anti-Cestodal Drugs.
Aside from praziquantel, there are other anti-cestodal drugs out there that have some activity against many of the parasitic tapeworms, including Taenia, infesting dogs and cats. I will not make huge mention of them, aside from the basic points below, because many of them are going out of fashion, many are hard to get, most have only a very narrow range of tapeworm activity, many don'tkill hydatids and some have significantly toxic side effects when used in domestic animals. I would not recommend using any of thebelow-mentioned drugs to treat hydatid tapeworms in domestic pets (especially dogs and cats) if you have access topraziquantel (see your vet). Praziquantel is the best as far as I can tell.
Prevents the tapeworm from making energy (ATP) from glucose (thus it dies).
Has been used against adult intestinal tapeworms in dogs and cats and people.
Good activity against Taenia. Variable activity against Dipylidium and unreliable againstEchinococcus (not reliable for breaking the hydatid tapeworm life cycle). Not satisfactory forEchinococcus prevention (therefore not an ideal drug to use in dogs).
Often a first choice in the treatment of Taenia saginata in people. Can be used alone or concurrentlywith praziquantel.
Minimal absorption from the intestinal tract and therefore toxicity is low (when used orally).
Must be given on an empty stomach.
Thought to be safe in pregnant or debilitated animals.
Toxic to fish and waterways.
Has been used on tapeworms in dogs and cats.
Good activity against Taenia. Fair to good activity against Echinococcus, but variable activity againstDipylidium (not reliable for breaking the flea tapeworm life cycle).
Must be given on an empty stomach.
Has been known to have significant toxic side effects, including the death of pets.
Has been used on tapeworms in dogs and cats.
Good activity against Taenia. Fair to good activity against Dipylidium, but unreliable againstEchinococcus (not reliable for breaking the hydatid tapeworm life cycle).
Minimal absorption from the intestinal tract, so toxicity is thought to be low (when used orally).
Mainly used to kill tapeworms and flukes in livestock animals, not domestic pets.
Good activity against Taenia and Echinococcus.
Tests on dogs have found that this drug can have significant toxic side effects in this species (cats unknown but probably of similar risk).
Toxicity concerns make it unfavourable for tapeworm control when better drugs are available.
Has been used on tapeworms in dogs and cats and many other animal species.
Good activity against Taenia, but variable to low activity againstDipylidium (not reliable for breaking the flea tapeworm life cycle).
Has been known to have toxic side effects in domestic pets (vomiting, diarrhea), but for the most part iswell-tolerated by dogs and cats.
Apparently effective at killing hydatid tapeworms in dogs.
I can not vouch for its safety.
Effective on Taenia.Apparently effective at killing hydatid tapeworms in dogs (7.5mg/kg).
I can not vouch for its safety.
Benzimidazole drugs (Mebendazole, Fenbendazole and so on):
Many types of benzimidazole drugs have been studied in order to assess their effects against tapeworms in dogs and cats.
Most of them show good activity against Taenia and some even show good activity against Echinococcus, but none of themis any good for treating Dipylidium (i.e. not reliable for breaking the flea tapeworm life cycle).
Benzimidazoles have been known to have significant toxic side effects in dogs and cats and other species.
Benzimidazoles are sometimes used to sterilise hydatid cysts in intermediate host animals prior to their surgical removal.
Albendazole has been used to kill Taenia solium and hydatid cysts in people prior to their surgical removal or in cases where such surgical removal is impossible.
Praziquantel and albendazole together were used to treat a woman infested with cysticerci of Taenia crassiceps (ref 9) to good effect.
Mebendazole orally has been used to treat Taenia saginata infestations in people.
NOTE - Please read our disclaimer before attempting to self-diagnose and dose your animals withany drugs mentioned on these pages. Pet Informed is a general advice website only and mistakes can bemade - we always recommend that you double-check any of our information with your own vet. Again, if you haveaccess to praziquantel (and all vets usually do), I would use this drug over any of the other tapeworm-killing drugsmentioned here.
4) Some basics on human Taenia saginata, Taenia solium and atypical Taeniid tapeworm infestations and the prevention of tapeworm disease (especially pork tapeworm cysticercosis) in people.
Most of this information on Taenia solium pork tapeworm and Taenia saginata beef tapeworm has already been discussed in great detail in sections 1 and 2 of this Taenia tapeworm life cycle webpage. This section (section 4) just summarises it in one block forthose of you who are specifically interested in human tapeworm infestations. If you haven't read sections 1 and 2 of this page, I recommend that you take a look as these sections containdetailed info on how the Taenia life cycle actually works, how Taenia tapeworms are contracted andwhat side effects and disease effects can occur as a result of Taenia infestations. The finalpart of this section (4c) describes atypical infestations of humans with other species of Taeniid - a topic which has not been covered previously in this webpage.
4a) Tapeworms in Humans 1 - Taenia saginata beef tapeworm:
Taenia saginata is a very long (3-25 meters in length) tapeworm parasite, whose adult formis found attached to the small intestinal tracts of human beings. In man it has been known to live for around20 years within a single individual.
In low to medium numbers, these tapeworms cause minimal side effects in their human hosts (see section2b on symptoms seen in definitive host animals). Many people might not ever be aware that they have a tapewormdwelling inside of them, they can be that benign. At best, their presence (particularly if they are large in size)might be enough to cause intestinal cramping, mild nausea and appetite fluctuations (oftenblamed on other causes) and when their segments (proglottids) start to shed out into the feces, this processmight be associated with anal pruritis (irritation and itchiness of the anus). More than likely, mostpeople will only discover that they have a tapeworm because they have spotted segments and lengths ofthe worm turning up in their feces (i.e. not because of any actual disease symptoms).
In high numbers and sizes, particularly in otherwise-compromised host humans, beef tapewormsmight pose some clinical risk to their human hosts. They can be associated with: nausea, appetite loss or gain, vomiting, weakness, dizziness, headaches, malnutrition, weight-loss, intestinal obstruction, intestinal perforation, appendicitis, pancreatitis, biliary obstruction, diarrhea, anal irritationand abdominal pain and cramping. Some people seem to be allergic to the proteins shed by theworms and can even develop a form of allergic inflammatory bowel disease from them (which should go away if the worms are treated). A severe intestinal obstruction could be enough to cause the deathof an individual (particularly a child) if it remains undiagnosed and detected. Likewise, shoulda tapeworm manage to perforate the bowel (resulting in infection of the human abdominal cavity) or obstructthe biliary duct, cecum, appendix or pancreatic duct, nasty, life-threatening complications can result.
http://www.dpd.cdc.gov/dpdx/html/imagelibrary/s-z/taeniasis/body_Taeniasis_il5.htm - Taenia saginata.
http://missinglink.ucsf.edu/lm/virus_and_parasites/taenia.html - Some nice images of Taenia saginata and Taenia soliumeggs, proglottids and scolices (useful for comparing the two species).
The tapeworm is caught through the consumption of undercooked cattle meat (beef, steak, mince) or cow heart muscle,which bears the small (~10mm), white, cystic larval (cysticercus) forms of the juvenile beef tapeworm (see section 1on the tapeworm life cycle for information about the larval stages of Taeniid tapeworms present in the bodies of intermediate host animals like cattle). Such cyst-infested beef is sometimes termed 'measly beef' because it has white spotsall over it. Humans who like to indulge in raw (tartare-style) or quick-seared (blue-style) undercooked beef are at high risk of catching Taenia saginata tapeworms should the meatthey are consuming be infected with juvenile tapeworm cysts.
Author's note - several references suggested that, even though the cow is the main intermediate host, it is possiblefor T. saginata cysts to be present in the meat of such animals as buffalo, llamas, giraffes, reindeer (possibly other largecaribou-types too) and even sheep and goats. These meats should also be considered of some risk to humans withregard to the contraction of T. saginata. They should only be eaten well-cooked.
Adult beef tapeworms can not be passed directly from human to human. The consumption of cyst-affected meat must be involved.
Preventing beef tapeworms is easy. Only eat very well-cooked (i.e. the centre of the meat must reach >56 degrees Centrigradeto be termed well-cooked); previously frozen (beef that has been frozen to -5C for over a week should also be safe) or well-processed beef or don't partake in livestock meat at alland you should not get the parasite. Smoked and pickled meat can contain active cysts so do not consider these safe in all situations.
If you do like the taste of beef tartare (raw meat)or blue steak (barely-seared steak) then make sure that the source of the beef is a high-quality,vet-inspected abattoir. Most good abattoirs screen their meat for cysts and affected meat is generallyculled from the human supply chain (it might go into pet food, which is OK because pet food is well-cookedand dogs and cats don't catch adult T. saginata). Be aware, however, that even in good meat inspection situationsit is possible for around 1/4 of all cyst-infected meat to be missed and therefore passed as safe for human consumption. I would certainly not eat any undercooked meat from a secondor third world country as there is a greater risk of poor or absent meat-screening practices being employed by such countries.
http://www.cfsph.iastate.edu/DiseaseInfo/clinical-signs-photos.php?name=taenia - A nice Taenia link discussing food security and public health issues pertaining to Taeniids.
http://cal.vet.upenn.edu/projects/paraav/images/lab7-16.jpg - hundreds of Taenia saginata cysticerci in a cow's heart.
http://www.cfsph.iastate.edu/DiseaseInfo/ImageDB/TAE/TAE_002.jpg - Taenia cysts in the muscles of cattle.
Preventing the cattle from contracting the meat cysts can also help communities to reduce the incidenceof human tapeworm infestations. Making sure that cattle have access to pastures and water supplies that arenot contaminated by human sewage (e.g. no human effluent or human feces used in irrigation or fertilisation ofcrops) can go a long way towards preventing the cow meat from becoming contaminated. Cattle should also not be given access to places where feces might be found as they will deliberately consume human droppings(who knows why, but they do).
Cattle can also be vaccinated against Taenia, however, this is not often done routinely. Only farms thathave had outbreaks of Taenia saginata and their meat condemned from sale are likely to take upthe vaccines. It is unlikely that farms in developing countries (where the vaccines probably are needed) wouldhave much access to the vaccines because of cost and vaccine-storage (refrigeration) limitations.
Treatment of adult beef tapeworms in man requires the administration of an anti-cestodal medication (as mentionedin the section on tapeworm treatment - section 3). You will not typically find anti-tapeworm drugs inmost routine, over-the-counter human intestinal wormers (I looked in my local pharmacy and couldn't find any medication that contained praziquantel or similar). This is probably because tapeworms arenot all that common in first-world countries (due to overall good hygiene and meat-processing standards) and because the authorities do not want the over-use of products like praziquantel to result in the developmentof praziquantel drug resistance by extra-nasty parasites like Taenia solium andSchistosoma (which are also treated using praziquantel, among other drugs).
If you have found tapeworm segments in your feces, you should see your doctor for theprescription of an appropriate treatment. Also, if you can (it sounds revolting), take thetapeworm segment/s along with you to the doctor (collect and wash the worm using disposable gloves and put it in a jar of saline - do not touch any of the faeces). The segments need to be fresh to be of use (old segments break down and are of no diagnostic use). Your doctor should take steps to identify the tapeworm species because although Taenia saginatais fine to have and won't generally hurt anyone, Taenia solium (the pork tapeworm) is of HUGE disease and human health significance and needs to be diagnosed if it is present!
Tapeworms in Humans - 'Asian Taenia' or Taenia saginata asiatica:
There is a species of tapeworm that is very closely related to Taenia saginata, which has been found insouth-east Asia and China. Sometimes called Taenia saginata asiatica or "Asian Taenia", its adult form lives inthe digestive tract of human beings. Instead of being found in the meat of cattle, however, the cystic, larval formof this particular Taeniid tends to reside in the offal (organs), particularly the liver, of pigs.
Taenia saginata asiatica is of similar, minor disease significance to man as Taenia saginata beef tapeworm is, however, its larval presence in porcine animals (swine) means that morecare must be taken to identify and differentiate this species from Taenia solium (a tapeworm species that is much more dangerous to humans), which is also found in pigs. Taenia saginata asiatica tends to favour the internal organsof the pig (particularly the liver), whereas Taenia solium tends to occupy the internal organsand the muscles of the pig (spotting lots of cysts in the muscles of the pig makes Taenia solium more likely).Identifying spines on the rostellum of the adult worm is not useful in telling the two species apartbecause, while adult Taenia saginata (beef tapeworm) lacks spines and adult Taenia solium has them, theadult Taenia saginata asiatica worm does have rostellum spines (unlike T. saginata) and so looks very similarin appearance to Taenia solium in this regard.
4b) Tapeworms in Humans 2 - Taenia solium pork tapeworm:
Taenia solium is a very very dangerous tapeworm parasite whose adult form is found attached to the small intestinal tract of human beings. Generally found in developingcountries (south-east Asia, South and Central America, India, China, sub-Saharan Africa and parts of Europe),the worm is considered a parasite of high human health concern and should never be taken lightly. It is endemic inMexico (a country of high-risk).
Taenia solium has been known to live for around 25 years within a single individual.
Human Taenia solium - Signs of Infestation:
The adult form of the tapeworm (present in the human intestine) is not of particular concern to us, disease-wise, as it probably only produces the same mild, non-specific symptoms of intestinal discomfort,nausea, diarrhea and anal irritation as previously described for Taenia saginata (except if it is present inlarge numbers, of course, where more severe symptoms might be present). The danger with the adult form ofTaenia solium lies in the fact that it sheds eggs that are directly infective to man (i.e.can be passed directly from human to human).
Humans who inadvertently consume their own egg-laden feces or those of another T. solium infested person may develop a multitude of expanding, life-threatening larval cysts, imbedded throughout their internal organs (including the brain). These cysts can range in size from 0.5-20cm in diameter. If enough of them are present and/or they are located in 'bad spots' within the human body (e.g. the brain, the lung) the affected person can suffer from extreme disability and even death! The parasite should not be taken lightly.
Note - one reference (8) suggested that dogs, cats, bears and primates may occasionally be infested with life-threatening cysticercosis through the consumption of Taenia solium egg-infested human feces. Such animals would be considered end-stage, accidental hosts for the parasite (termed paratenic hostswith regard to the tapeworm life cycle). The infested animal would rarely get to pass its cysts onto a human definitive host because humans rarely consume the meat and organs of such animals.
http://images.medscape.com/pi/features/slideshow-slide/neurocysticercosis/fig1.jpg - Taenia solium cysts in a human brain.http://img.medscape.com/pi/emed/ckb/pediatrics_general/996090-997096-2598.jpg - an MRI image of a human brain infested with cystic Taenia solium lesions.
http://www.neurology.org/content/vol53/issue7/images/small/G3510F1.gif - another human brain containing Taeniid cysticerci.
http://www.aans.org/bulletin/images/Vol17_3_08/OcularCysticercosis_small.jpg - a Taenia cyst in a human eye.
How People Catch Adult Taenia solium tapeworms:
The adult tapeworm is caught through the consumption of undercooked pig meat (typically pork,as ham, bacon and sausages tend to be heavily cooked and processed - killing the cysts), pig heart muscle or pig offal,which bears the cystic larval (cysticercus) forms of the juvenile pork tapeworm (see section 1on the tapeworm life cycle for information about the larval stages of Taeniid tapeworms present in the bodies of intermediate host animals like pigs). Humans who like to indulge in raw (tartare-style) or quick-seared (blue-style) undercooked pork or pig offal are at high risk of catching Taenia solium tapeworms should the tissuethey are consuming be infected with juvenile tapeworm cysts.
Author's note: eating the undercooked meat or organs of fellow humans who have died of T. solium cystscould also give the cannibal diner a dose of adult Taenia solium. I make mention of this because thereare tribes in Asia and other parts who still practice cannibalism. A Taenia solium life-cyclecould be maintained in such parts if humans ate the cyst-infected meat of their fellows and then passedthe resultant adult-tapeworm's eggs onto their fellow civilians.
http://www.cfsph.iastate.edu/DiseaseInfo/ImageDB/TAE/TAE_001.jpg - Taenia solium cysts in the muscles of a pig (pork cysts).
http://www.medicine.cmu.ac.th/dept/parasite/cestode/Tsolium_whole_worm.htm - adult T. solium parasite.
http://missinglink.ucsf.edu/lm/virus_and_parasites/taenia.html - Some nice images of Taenia saginata and Taenia soliumeggs, proglottids and scolices (useful for comparing the two species).
Before you panic about that undercooked pork-kebab you had last night, do be aware of course thatTaenia solium has, for the most part, been kept out of most developed countries by strict quarantine practicesand abattoir-screening and hygiene standards. Eating raw pork grown only in Australia is unlikely to give youT. solium (it's still never advisable to eat raw meat, of course), whereas, the consumption of raw or undercooked pork grown in south-east Asia, South and Central America and Africa may well be cause for T. solium concern. Taenia saginata, on the other hand, is generally present in most countries so the eating of raw or undercooked beef anywhere is of some risk when it comes to this parasite.
How People Catch Larval Taenia solium tapeworms:
The juvenile (cysticercus) forms of the Taenia solium tapeworm are contracted by humans through theconsumption of small amounts of human feces, which bear the eggs of the adult tapeworm. These eggs, onceingested, result in the formation of life-threatening larval cysts within the organs of the consumer. Therisk of egg ingestion is highest for the person who actually carries the adult tapeworm (a small lapse in toilet hygienecould result in the adult-tapeworm-carrier consuming some eggs), however, other peoplecan get the eggs if the carrier is not very hygienic with his/her toileting practices (e.g. doesn'twash his/her hands after using the toilet and so on).
Also be aware of the role of water in the transmission of T. solium eggs to people. If tapeworm-infestedpeople happen to defecate into the local waterways, it is possible for other people to develop T. solium cysts by drinking the egg-contaminated water.
As a tourist to a Taenia solium endemic country, also be aware of the farming practices of the places you are visiting. Some countries fertilise their crops, vegetables and fruits with human effluent, which could easily harbor infective tapewormeggs. Eating such food matter raw and unwashed could result in the intake of tapeworm eggs.
Insects (e.g. flies) can also transfer tapeworm eggs. A fly can land on tapeworm-egg infected human poo, pick up the eggs with its feet and then fly onto a person's food, depositing the infective eggs into the meal.
Finally, it is important to mention that sometimes the intestinal contractions of the digestive tract can force gravidTaenia solium segments upwards into the stomach of the tapeworm-infested person, instead of out throughthe colon and anus. In these situations, the digestive juices of the stomach will digest away the proglottidsegment, resulting in a mass release of hundreds of infective eggs into the person's digestive tract. The larvaefrom such eggs will rapidly enter the person's body and disseminate everywhere, resulting in a massiveinfestation of cysticerci all over the body. The images of the human brains filled with hundreds of cysticerciof Taenia solium probably arose from just such events. This is rare, but when it occurs, it is devastating forthe victim.
How To Avoid Catching Taenia solium:
Preventing adult pork tapeworms is easy. Only eat very well-cooked (i.e. the centre of the meat must reach >56 degrees Centrigrade to be termed well-cooked); previously frozen (pork that has been frozen to -5C for over 2 weeks should also be safe) or well-processed pork or don't partake in pork at alland you should not get the adult parasite. Smoked and pickled pork can contain active cysts so do not consider these safe in all situations.
If you do like the taste of pork tartare (raw meat) or blue pork steaks (barely-seared steak) then make sure that the source of the pork is a high-quality,vet-inspected abattoir and, even then, only eat it in a country that does not have T. solium. Most good abattoirs screen their meat for cysts and affected meat is generallyculled from the human supply chain (it might go into pet food, which is OK because pet food is well-cookedand dogs and cats can't catch T. solium). Be aware, however, that even in good meat inspection situationsit is possible for around 1/4 of all cyst-infected meat and offal to be missed and therefore passed as safe for human consumption. I would never eat any undercooked pork (or pork full-stop)from a second or third world country as there is a greater risk of poor meat-screening practices being employed by such countries. Also, T. solium tends to be found mainly in developing countries.
Preventing juvenile pork tapeworm cysts (cysticercosis) is not so straight-forward or simple.Naturally, you need to exercise good hygiene in the bathroom (good hand-washing aftergoing to the toilet) so that, should you be unlucky enough to carry an adult T. solium tapeworm, you do not inadvertently consume the tapeworm eggs from the consumption of your own stoolsor pass these eggs onto other people.
The trouble is, not everyone else exercises such good hygiene,making the organism almost impossible for you to prevent, unless you don't eat anything! You could, for example, go to a restaurant in Mexico or southern Asia and be served a salad (no pork) by a T. solium carrying chef who just went to the bathroom and did not wash his hands. That chef could have puttiny amounts of his feces into your meal, containing T. solium eggs that you will then consume inthat salad, resulting in cysticercosis. You didn't know the man was infested. You didn't know he didn'twash his hands. You enjoyed your salad. I'm not sure what you can do about thisto prevent it. If you are in a T. solium country, you should probably prepareas much of your own food as you can, sourcing it from overseas sources and cooking it as well as you can. If you need to eat out, go with cooked options from restaurants of high quality food standards(i.e. not backlot restaurants or street vendors) and don't eat from buffets or salad bars where other people couldhave touched the food. Using disposable cutlery where possible is also recommended so thatyou don't catch eggs from under-cleaned cutlery
Also be aware of the role of water in the transmission of T. solium eggs to people. If infestedpeople defecate into the waterways, you could get T. solium if you drink the contaminated water. Be sure to thoroughly boil any water in T. solium countries or, even better, source your water from a treated source or use bottled water.
Also be aware of the farming practices of the places you are visiting. Some countries fertilise their crops, vegetables and fruits with human effluent, which could easily harbour infective tapewormeggs. Eating such food matter raw and unwashed could result in the intake of eggs. Vegetables and fruits should be cookedor, at bare minimum, washed and scrubbed and, if possible, peeled, prior to ingestion.
Insects (e.g. flies) can also transfer tapeworm eggs. A fly can land on tapeworm-egg infected poo, pick up the eggs with its feet and then fly onto your food, depositing the infective eggs into your meal. Be aware of this and keep them away. Do not leave uncovered food out on open benches where it canbe contaminated.
Also be aware of the role of pigs in keeping T. solium active in communities. It is common in many third worldcountries (e.g. countries in Asia, Africa and South and Central America) for pigs to be a major source ofwealth and food. Pigs wandering freely around the townships may become infested with T. solium cyststhrough the consumption of human feces. Such pigs, eaten by the community, result in the transmissionof adult Taenia solium tapeworms into the human population. Lapses in human hygiene can then resultin the tapeworm eggs being consumed by the local people, causing mass cysticercosis. As a traveler to Taeniasolium regions, you should be very aware of the heightened risk of contracting cysticercosis should you visit and eat-in rural townships with a strong pig presence (the likelihood of T. solium is very high).
Preventing the swine from contracting the meat cysts can help communities to reduce the incidenceof nasty human tapeworm infestations. Making sure that pigs have access to food sources, pastures and waterways that arenot contaminated by human sewage (e.g. no sewage used in irrigation or fertilisation) can go a long way towards preventingthe meat from becoming contaminated. Pigs can possibly also be vaccinated against Taenia. Breaking the life cycle in this way can reduce the chances of humans contracting the parasite.
How To Treat Taenia solium:
Treatment of adult pork tapeworms in man requires the administration of an anti-cestodal medication (as mentionedin the section on tapeworm treatment - section 3). You will not typically find anti-tapeworm drugs inmost routine, over-the-counter human intestinal wormers (I looked in my local pharmacy and couldn't find any medication that contained praziquantel or similar). This is probably because tapeworms arenot all that common in first-world countries (due to overall good hygiene and meat-processing standards) and because the authorities do not want the over-use of products like praziquantel to result in the developmentof praziquantel drug resistance by extra-nasty parasites like Taenia solium andSchistosoma (which are also treated using praziquantel, among other drugs).
If you have found tapeworm segments in your feces, you should see your doctor for theprescription of an appropriate treatment. If you are living in a first-world country, it willprobably only be T. saginata, but if you want to be sure (it sounds revolting), take thetapeworm segment/s along with you to the doctor (collect and wash the worm using disposable gloves and put it in a jar of saline - do not touch any of the faeces). The segments need to be fresh to be of use (old segments break down and are of no diagnostic use). Your doctor should take steps to identify the species because although Taenia saginatais fine to have and won't generally hurt anyone, Taenia solium (the pork tapeworm) is of HUGE disease and human health significance and needs to be diagnosed if it is present!
Be sure to notify your doctor if you have recently (within the last 2-3 years) beenin south-east Asia, India, China, Africa or Southern or Central America (particularly if you could have eaten pork).
Treatment of larval pork tapeworms in the organs of a human (cysticercosis) is trickier. The removal certainlyrequires the services of a specialist doctor and it is likely that surgery will be required tomanually remove the cysts from the organs. Body scanning (e.g. MRI, ultrasound) will most likelybe used to diagnose and locate the cysts within the human body and/or brain. Some cyststhat can not be removed easily (e.g. certain brain and eye cysts) are killed using albendazoleand corticosteroids (to reduce the secondary inflammation caused by the cyst's death). Sometimespraziquantel in high doses is used to kill the cysts, but albendazole is generally favoured.
4c) Tapeworms in Humans 3 - accidental, possibly opportunistic, human tapeworm infestations posed by other Taenia species:
Up until this point, I have taken great pains to suggest that each Taeniid tapeworm species tends to exhibit a high degreeof specificity and preference for the species of definitive and intermediate host animals it infests (e.g. Taeniacrassiceps infests foxes and rodents; Taenia ovis infests dogs and sheep; Taenia saginata infests humans and cattle and so on). Very simplistic and easy to understand.
The trouble is, this generalization does not always hold true. As DNA identification of parasite species (includingtapeworms) becomes more advanced, we are starting to discover more and more cases of crossing-over occurringbetween these parasites with regard to their hosts. Several cases have now been reported ofhumans developing cysticercosis and coenurosis (potentially-life-threatening internal tissue infestations with the cystic larval tapeworm forms - similar to the situation described above with Taenia solium) from such non-human species of tapeworm as: Taenia crassiceps, Taenia multiceps, Taenia serialis,Taenia brauni, Taenia ovis, Taenia hydatigena and even Taenia saginata (i.e. self-infectionof a human with his own tapeworm eggs, similar to the situation described for Taenia solium). The strobilocercus cyst of the cat tapeworm: Taenia taeniaeformis has, in exceptionally rare instances, also been found in the tissues of humans.
Author's side note: One reference did say that several cases of Taenia saginatacysticercosis in people were later found to be the result of cyst misidentification (i.e. that another Taeniidand not Taenia saginata was responsible). Such atypical cystic infestation with Taenia saginata is thought to be very rare in humans. As DNA identification of parasites becomes more commonplace, the incidence of misidentification of cyst-species is likely to reduce in the future.
In the case of Taenia crassiceps, such an infestation could be quite dangerous for the human concerned, given that the cysticerci of T. crassiceps demonstrate a bizarre habit of budding (multiplying in number within the intermediate host tissues they are occupying). Should such cystic budding happen within the lung, liver or brain, the consequences could be quite devastating for the person affected.In the case of Taenia multiceps, such human infestation could likewise be very dangerous for the human concerned because the larval cyst form of Taenia multiceps is a coenurus (i.e. a very large cyst with multiple scolices) and because the cyst tends to favour the intermediate host's brain as a site for invasion (resulting in brain damage and even death).
In order to develop such an atypical larval cyst infestation, the human concerned has to have consumed the egg/s of the tapeworm species in question at some point in time. The person could have consumed the egg/s inadvertently, through close contact with environments inhabited by tapeworm-infested foxes, dogs or wild canids (canine species are the major definitive host carriers of most adult Taeniids, aside from Taenia taeniaeformis of cats). Alternatively, the person could have eaten raw food (e.g. greens) or drunk water that had been contaminated with tapeworm-egg-infested definitive host animal feces. There are many ways that such a person could consume an atypical tapeworm egg, resulting in the development of larval tapeworm cysts within the tissues of the human patient.
Author's note: People can inoculate the eggs of such Taeniids as Taenia multiceps, Taenia serialisand Taenia brauni directly into their eyes by rubbing egg-infested fecally-contaminated dirt into their eyes (e.g. a child playing in a feces-contaminated sandpit might accidentally do this). Once in the eye, these microscopic tapeworm eggs can find their way into the human intestinal tract via the nasolacrimal ducts and throat.
Such rare, atypical infestations, when they occur, generally (but not always) occur in human patients who have low or weak immune systems. Patients with cancer, immune diseases, HIV (AIDS) or who have recently been on chemotherapyor immune-suppressant drugs are particularly at risk. This suggests that the immune system of the individual person plays a big role in whether such non-human-attracted tapeworm cysticerci are actually able to take hold within a person's tissues and grow. It is probably also the reason why such atypical tapeworm cyst infestations are currentlyconsidered rare in the medical world. As more and more people develop immune suppressive diseases (AIDS or HIV, lymphoma, bone marrow cancers and so on) or receive immune-suppressive treatments to treat cancers and autoimmune diseases, the number of cases of atypical larval tapeworm cysticercosis is likely to rise in the medical literature.
Humans need to ensure that they exercise high standards of personal hygiene (bathing, hand-washing) after they have beenvisiting environments that are home to definitive host animals, particularly canines (e.g. wilderness areas, forests, dog and cat shelters, pounds and so on). People should also be vigilant in maintaining the tapeworm-free status of their own dogs and cats through regular tapeworming prophylaxis. Lab workers and research personnel working with wild canids and foxes must ensure that they exercise good hygiene after handling such animals (eggs can be present on the animal's fur). They should be careful not to touch stool samples with their bare hands and they shouldensure that there is no fecal contamination of laboratory rooms and equipment.
Humans should also be aware of the role of water in the transmission of Taenia eggs to people. If infesteddogs, cats or people defecate into the local waterways, you could get a Taeniid if you drink the egg-contaminated water. Be sure to thoroughly boil any water you drink or, better, source your water from treated sources (or use bottled water).
Also be aware of the farming practices of the places you are visiting. Some countries and cultures fertilise their crops, vegetables and fruits with raw effluent, which could easily harbour infective tapeworm eggs. Eating such food matter raw and unwashed could result in the consumption of tapeworm eggs. Vegetables and fruits should be cookedor, at bare minimum, washed and scrubbed and, if possible, peeled, prior to ingestion.
Insects (e.g. flies) can also transfer tapeworm eggs. A fly can land on tapeworm-egg infected poo, pick up the eggs with its feet and then fly onto your food, depositing the infective eggs into your meal. Be aware of this and keep them away. Do not leave uncovered food out on open benches where it canbe contaminated.
Author's note: Similar atypical cysticercus infestations have been found in dogs and cats (animalswho are typically definitive hosts, not intermediate hosts) who have inadvertently consumedtapeworm eggs from their own feces or fromthe feces of other types of definitive hosts (e.g. foxes, cats, dogs, wild canids). This is all the more reason to maintain your own pet's worming and not let him/her eat animal feces when out inthe local environment.
A beautiful case study (complete with photos) of a woman infested with the buddingcysticerci tapeworm larvae of Taenia crassiceps.
A brilliant public health article on Taeniids infesting humans.
5) Your Taenia tapeworm life cycle links:
To go from this Taeniid tapeworm life cycles page to the Pet Informed Home Page, click here.
To go to the Flea Tapeworm page, click here.
To go to the Hydatid Tapeworm page, click here.
http://bioweb.uwlax.edu/bio203/s2008/geske_rich/index.html - an excellent, simple resource on Taenia solium.
http://www.stanford.edu/group/parasites/ParaSites2006/Taenia_saginata/index.html - an excellent, simple resource on Taenia saginata.
http://www.stanford.edu/group/parasites/ParaSites2006/Taenia_solium/index.html - an excellent, simple resource on Taenia solium.
http://www.ajtmh.org/cgi/reprint/75/1/108.pdf - an interesting case study about a human infestedwith the budding cysticerci of Taenia crassiceps.
http://gateway.nlm.nih.gov/MeetingAbstracts/ma?f=102217225.html - information on atypical Taenia infestations and HIV.
http://www.cfsph.iastate.edu/Factsheets/pdfs/taenia.pdf - a nice article on human Taenia infestations.
Taenia Tapeworm Life Cycle References and Suggested Readings:
1) Helminths. In Bowman DD, Lynn RC, Eberhard ML editors: Parasitology for Veterinarians, USA, 2003, Elsevier Science.
2) Phylum Platyhelminthes. In Hobbs RP, Thompson ARC, Lymbery AJ: Parasitology, Perth, 1999, Murdoch University.
3) Tapeworms. In Schmidt GD, Roberts LS: Foundations of Parasitology, 6th ed., Singapore, 2000, McGraw-Hill Higher Education.
4) Cestoidea: Form Function and Classification of the Tapeworms. In Schmidt GD, Roberts LS: Foundations of Parasitology, 6th ed., Singapore, 2000, McGraw-Hill Higher Education.
5) Roberson EL, Anticestodal and Antitrematodal Drugs. In Booth NH, Mc Donald LE: Veterinary Pharmacology and Therapeutics 6th ed., Iowa, 1988, Iowa State University Press.
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Please note: the aforementioned tapeworm prevention, Taenia tapeworm control and Taenia tapewormtreatment guidelines and information on the Taenia tapeworm life cycle are general information and recommendations only. The information provided is based on published information and on relevant veterinary literature and publications and my own experience as a practicing veterinarian.The advice given is appropriate to the vast majority of pet owners, however, giventhe large range of tapeworm varieties out there and the large range of tapeworm medication types and tapeworm prevention and control protocols now available, owners should take it upon themselves to ask their own veterinarian what treatment and tapeworm prevention schedules s/he is using so as to be certain what to do. Owners with specific circumstances (e.g. high and repeated tapeworm infestation burdens in their pets; high-transmission situations, hunting situations, farming situations, hydatid-tapeworm zones, pregnant bitches and queens; very young puppies and kittens; livestock and poultry producers; multiple-dog and cat environments;animals on immune-suppressant medicines; animals with immunosuppressant diseases or conditions; owners of sick anddebilitated animals etc. etc.) should ask their vet what the safest and most effective tapeworm control protocol is for their situation. Humans with tapeworm concerns should see their doctor.
Please note: the scientific tapeworm names mentioned in this Taenia tapeworm life cycle article are only current asof the date of this web-page's copyright date and the dates of my references. Parasite scientific names are constantly being reviewed and changed as new scientific information becomes available and names that are current now may alter in the future.