''Taenia pisiformis'', commonly called the rabbit tapeworm, is an endoparasitic

tapeworm Eucestoda, commonly referred to as tapeworms, is the larger of the two subclasses of flatworms in the class Cestoda (the other subclass is Cestodaria). Larvae have six posterior hooks on the scolex (head), in contrast to the ten-hooked Cesto ...

which causes infection in

lagomorph The lagomorphs are the members of the taxonomic order Lagomorpha, of which there are two living families: the Leporidae (hares and rabbits) and the Ochotonidae (pikas). The name of the order is derived from the Ancient Greek ''lagos'' (λαγ� ...

rodent Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are n ...

s, and

carnivore A carnivore , or meat-eater (Latin, ''caro'', genitive ''carnis'', meaning meat or "flesh" and ''vorare'' meaning "to devour"), is an animal or plant whose food and energy requirements derive from animal tissues (mainly muscle, fat and other s ...

s. Adult ''T. pisiformis'' typically occur within the small intestines of the

definitive host In biology and medicine, a host is a larger organism that harbours a smaller organism; whether a parasitic, a mutualistic, or a commensalist ''guest'' ( symbiont). The guest is typically provided with nourishment and shelter. Examples include ...

s, the carnivores. Lagomorphs, the intermediate hosts, are infected by fecal contamination of grasses and other food sources by the definitive hosts. The larval stage is often referred to as ''Cysticercus pisiformis'' and is found on the livers and peritoneal cavities of the intermediate hosts. ''T. pisiformis'' can be found worldwide.

Description

''T. pisiformis'' typically infect dogs and other carnivores such as

coyote The coyote (''Canis latrans'') is a species of canine native to North America. It is smaller than its close relative, the wolf, and slightly smaller than the closely related eastern wolf and red wolf. It fills much of the same ecological nich ...

s and foxes. In rabbits, ''T. pisiformis'' larvae attach themselves to the liver and intestines, forming cysts in diameter. This is referred to as

cysticercosis Cysticercosis is a tissue infection caused by the young form of the pork tapeworm. People may have few or no symptoms for years. In some cases, particularly in Asia, solid lumps of between one and two centimetres may develop under the skin. Aft ...

. In adult ''T. pisiformis'', the long hooks of the

scolex Cestoda is a class of parasitic worms in the flatworm phylum (Platyhelminthes). Most of the species—and the best-known—are those in the subclass Eucestoda; they are ribbon-like worms as adults, known as tapeworms. Their bodies consist of m ...

are on average and the short hooks are . The dimensions of the suckers are . They can have from 34 to 38 hooks, which can be up to in length. Adult ''T. pisiformis'' can grow between . The

intermediate host In biology and medicine, a host is a larger organism that harbours a smaller organism; whether a parasitic, a mutualistic, or a commensalist ''guest'' ( symbiont). The guest is typically provided with nourishment and shelter. Examples include ...

is represented by

hare Hares and jackrabbits are mammals belonging to the genus ''Lepus''. They are herbivores, and live solitarily or in pairs. They nest in slight depressions called forms, and their young are able to fend for themselves shortly after birth. The g ...

s and

rabbit Rabbits, also known as bunnies or bunny rabbits, are small mammals in the family Leporidae (which also contains the hares) of the order Lagomorpha (which also contains the pikas). ''Oryctolagus cuniculus'' includes the European rabbit sp ...

s, in which are found the mesacestoide (the larval stage) known as cysticercus pisiformis. This is found in the peritoneum of the intermediate host and can be ingested by the definite host when the dog or cat feeds on the viscera of such an infected intermediate.

Life cycle

Eggs are introduced into the environment through infected canine feces. In the feces are the gravid proglottids that house the ''T. pisiformis'' eggs that will eventually be released from the proglottid onto nearby vegetation. The eggs are then ingested by a rabbit or from any member of the ''

Leporidae Leporidae is the family of rabbits and hares, containing over 60 species of extant mammals in all. The Latin word ''Leporidae'' means "those that resemble ''lepus''" (hare). Together with the pikas, the Leporidae constitute the mammalian order ...

'' family. Once inside the rabbit's gut the larva or

oncosphere An oncosphere is the larval form of a tapeworm once it has been ingested by an intermediate host animal. The intermediate host must ingest the tapeworm's eggs either in food or water-- once this has happened, the eggs hatch and develop into onc ...

phase will then penetrate into the intestinal wall until they reach the blood stream. When the worm reaches the liver the larva transforms into a cysticercus form. This cysticercus will stay in the liver for about two to four weeks, then move to the

peritoneal cavity The peritoneal cavity is a potential space between the parietal peritoneum (the peritoneum that surrounds the abdominal wall) and visceral peritoneum (the peritoneum that surrounds the internal organs). The parietal and visceral peritonea are la ...

where it will wait for the definitive host to eat the rabbit. The definitive hosts are ether dogs or other members of the ''

Canidae Canidae (; from Latin, '' canis'', " dog") is a biological family of dog-like carnivorans, colloquially referred to as dogs, and constitutes a clade. A member of this family is also called a canid (). There are three subfamilies found withi ...

'' family. Once ingested the cysticercus finds its way into the intestine and attaches to the intestinal wall with hooks and suckers. After the worm has time to develop and grow in size, the gravid proglottids is released from the distal end of the parasite and passed in the feces to start a new cycle.

Adult morphology

The adult stage consists of a

with four suckers and an armed rostellum, a short neck region, a series of immature

proglottids Cestoda is a class of parasitic worms in the flatworm phylum (Platyhelminthes). Most of the species—and the best-known—are those in the subclass Eucestoda; they are ribbon-like worms as adults, known as tapeworms. Their bodies consist of ...

with undeveloped reproductive organs, a series of mature proglottids with fully developed male and female reproductive organs, and a series of gravid proglottids with an expanded uterus filled with eggs.

Pathology

In rabbits, there are not really defined clinical signs seen for any range of intensity except when there is an externally high intensity. In this case, rabbits look weak or ill. The major illness seen is signs of liver failure. In very few cases the cysts will migrate to the lungs or brain; these cases can cause breathing complication or seizures. In the most extreme cases, the rabbit will have sudden death. For dogs, there are normally no clinical signs seen for low to moderate infections. In highly infected cases the dog will experience blockage in the intestines. In all cases the proglottids will be seen in the feces.

Diagnostics

When looking for signs of infection in the intermediate host or definitive host, the signs are not very externally seen. For the intermediate host there will be between two and 20 pea-sized cysts found inside the liver. The cysts that are found have one scolex inverted to the middle of the cyst. This shape is called a ''cysticercus'', that is part of the ''metacestodes'' stage of life. The ones found in the liver form these bladders that are specifically called ''Cysticercus pisiformis'' for ''T. pisiformis''. These signs can only be seen when a necropsy is done to the rabbit. When looking for an infection in dogs there is a more straightforward method. There will be gravid proglottids with striated eggs seen in the feces. This can be found using a fecal float on a sample that can easily be done by a vet.

Treatment and prevention

''Taenis pisiformis'' infection is very hard to treat in wild rabbits and canines, but it is easier to control pet infections. One way to stop the infection is to prevent dogs from eating wild rabbits or rodents. If the infected rabbit is not eaten then the worm cannot finish its life cycle. Household rabbits usually do not get infected if they are strictly indoor pets, but infection can happen if they are let outside into open grasses. If the infection is already present then use one of these drugs:

Epsiprantel Epsiprantel (trade name Cestex) is a veterinary drug which is used as an anthelmintic against tapeworms such as ''Echinococcus granulosus''. Indications It is indicated for the removal of cestodes (tapeworms) in cats (''Dipylidium caninum'' and ...

Praziquantel Praziquantel (PZQ), sold under the brandname Biltricide among others, is a medication used to treat a number of types of parasitic worm infections in mammals, birds, amphibians, reptiles, and fish. In humans specifically, it is used to treat sc ...

Mebendazole Mebendazole (MBZ), sold under the brand name Vermox among others, is a medication used to treat a number of parasitic worm infestations. This includes ascariasis, pinworm infection, hookworm infections, guinea worm infections, hydatid disea ...

Niclosamide Niclosamide, sold under the brand name Niclocide among others, is an anthelmintic medication used to treat tapeworm infestations, including diphyllobothriasis, hymenolepiasis, and taeniasis. It is not effective against other worms such as flukes ...

, Bunamindine hydrochloride or

Fenbendazole Fenbendazole is a broad spectrum benzimidazole anthelmintic used against gastrointestinal parasites including: giardia, roundworms, hookworms, whipworms, the tapeworm genus '' Taenia'' (but not effective against '' Dipylidium caninum'', a comm ...

. This will kill the adult stage but not the cyst or egg stage, so several treatments may be needed. Daily doses of Praziquantel for about one to two weeks' time will be effective against larval cysticercosis in rabbits. One dose of Niclosamide or Praziquantel can be very effective in dogs.

Gallery

Image:Taeniapisiformis.jpg, ''Taenia pisiformis'' cross section Image:Taenia egg.JPG, ''Taenia pisiformis'' egg Image:Cysticercus pisiformis.jpg, ''Cysticercus pisiformis'' - the larva found in intermediate hosts Image:TaeniaPisiformisLabeledProglottid.jpg, ''Taenia pisiformis'' mature proglottid