Internal parasites that may attack pet rabbits range from nematodes (worms) to protozoans (intracellular parasites). Many infections result from exposure to dog and cat feces contaminated with infective eggs. Some internal parasites of rabbits may be transmitted to their owners. Good sanitation practices are the best prevention.
- Trichostrongylidae is rabbit stomach worm. Rabbits get infected upon ingesting worm eggs. Parasite develops to maturity in stomach. The infestation with these worms usually has no clinical signs. In severe infections failure to gain weight or weight loss may be seen. Treatment is with Fenbendazole in feed for 5 days.
- Passalurus ambiguus is rabbit pinworm located in cecum and large intestine. The infestation with these worms usually has no clinical signs, even in heavy infections. Rabbits get infected through ingestion of contaminated food and water. Spores are shed in the urine and can remain viable for months. Rabbit pinworms are not transmissible to humans. Pinworms are extremely common in rabbits and may be difficult to prevent even with good sanitation. Treatment is with Piperazine for two days in food or water or fenbendazole in feed for 5 days.
- Taenia pisiformis, Taenia serialis, and Cittotaenia variabilis are rabbit tapeworms. These parasites may be located in the small intestine, liver or connective tissue of muscles. Signs may include loss of appetite, lethargy, enlarged abdomen and swelling under skin. Tapeworms are transmitted through ingestion of feed (especially grass) contaminated with eggs. The primary host of most tapeworms that affect rabbits is the dog. Rabbits should not be allowed to eat grass in area where dogs run. Rabbits are the primary host of Cittotaenia, but this tapeworm is usually found in wild rabbits, rarely domestic rabbits.
- Eimeria stiedae (also known as Monocystis stiedae), Coccidium oviforme, and Coccidium cuniculi are protozoan parasites which cause hepatic coccidiosis. Signs are usually mild and may include loss of appetite, rough coat, weight loss, enlarged abdomen, lethargy, constipation and diarrhea. In this form of coccidiosis the parasites invade the liver and block bile ducts rather than forming colonies on intestine walls. This condition is more serious than intestinal coccidiosis. Jaundice may be present in advanced stages. Death is usually rare, except in young rabbits with heavy infections. Diagnosis is made through identification of oocysts in feces. Treatment involves several drugs that controls the organism until natural immunity develops. Excellent husbandry can eliminate coccidiosis or keep it to a low level. Infected rabbits can be eliminated from the population. Barrier systems may be used. It is important to prevent fecal contamination of feed and water. A 10% ammonia solution is lethal to oocysts. Young rabbits should be separated from the dam as soon as possible, since suckling rabbits are especially susceptible to coccidiosis. Vermin must be controlled, and it should be explained to animal caretakers that they can mechanically transmit the disease.
- Eimeria irresidua, E. magna, E. media, E. perforans are very common protozoan parasites that infest intestinal tract. Different species prefer various areas. These are transmitted by ingestion of sporulated oocysts. It is generally accepted that "night feces" which the rabbits eat, do not contain infectious oocysts. Rabbits may have no clinical signs. More severely affected rabbits (usually young) lose weight or fail to gain. Diarrhea, if present, can be intermittent to profuse and watery with mucus and blood; such animals have intense thirst. The parasitized intestinal epithelial cells die, and this may cause ulceration and accumulation of a mixed mononuclear exudate. Deaths are due to dehydration and secondary bacterial infections. In cases of extremely heavy primary infections, rabbits may die before oocysts are passed in the feces. Treatment and control is the same as for hepatic coccidiosis.
- Toxoplasma gondii, (also known as T. cuniculi), is a relatively rare protozoan parasite in rabbits, but can occur in households with cats. It is transmitted through ingestion of cat feces containing infective oocysts and also by the transplacental route. The parasites are located in the brain, lymph nodes, spleen, liver, kidneys, lungs, heart, and eyes. Acute disease is found most commonly in young rabbits. Sudden loss of appetite, fever, (greater than 104° F) and increased respiratory rate may be seen. Rabbits develop ocular and nasal discharge, become lethargic, and central nervous signs of localized or generalized convulsions may occur a few days after initial signs are noticed. Paralysis may develop, especially in the hindquarters. Death usually occurs 2 to 8 days after the onset of signs. In chronic disease found most commonly in older rabbits, loss of appetite and anemia are common signs. Rabbits may die suddenly or recover. The diagnosis is usually done by a combination of histopathological examination of lesions, identification of organisms, and blood tests. Although drug therapy may be used, treatment is usually not practical while good husbandry is essential. Most disinfectants are ineffective, but heating and drying will inactivate the oocysts. If toxoplasmosis is present with a colony, only seronegative animals should be used for breeding. Rabbits may be a significant reservoir for the disease in man.
- Sarcocystis cuniculi (also known as Sarcocystis leporum) is a rare protozoan parasite located in the heart and skeletal muscle. Transmission is by ingestion of trophozoites passed in feces. Light to moderate infections have no clinical signs. The cysts produce a strong endotoxin, sarcocystin, which has been associated with the observed lameness in heavily infected animals. Sarcocystis infections have been reported in humans, and it is thought that these cases probably represent transmission from animals.
- Giardia duodenalis (also known as Hexamita duodenalis and Lamblia cuniculi is a common parasite located in the small intestine. In severely affected animals diarrhea, weight loss, dehydration, lethargy, and low body temperature may result. It is most often seen in very young rabbits, often those from pet stores. The parasite is transmitted through ingestion of cysts from cat and dog feces. Nutritional supplements, heat, fluids, and parasiticides such as fenbendazole and oxyfenbenddazole are used to treat it. Antibiotics are sometimes prescribed. To prevent the infestation, dispose of all dog and cat feces promptly and wash hands afterwards. Cysts can remain on the hair of dogs and cats and could potentially be a source of infection. This rabbit parasite does not appear to be transmissible to man.
- Cryptosporidium cuniculus. The rabbit is an intermediate host of this protozoan. Cats are the definitive host. Rabbits in households with cats can potentially jump into the cat's litter box, step in infected cat feces, and then ingest oocysts when cleaning their feet. Infected rabbits may have no clinical signs, or may have fever and die within a few days. The infection is treated with parasiticides. Rabbit owners who also own cats should be very careful to keep the cat's litter box immaculately clean, to wash their hands after cleaning the litter box, and to keep the rabbits from using it, if possible.
- Encephalitozoon cuniculi, also known as Nosema cuniculi, is a protozoan parasite located in the brain and kidneys. Infected rabbits may have no signs. In acute disease, loss of appetite, convulsions, increased thirst, urinary incontinence, wry neck, muscle weakness, paralysis of hindquarters, or sudden death may occur. The disease mainly affects kidneys and brain, although in seriously infected rabbits all tissues can be affected.
There is currently no drug therapy that cures encephalitozoonosis, although some drugs have been used to stabilize the affected animals. Some rabbits recover without treatment. Dwarf rabbits appear to be more susceptible than other rabbits. Encephalitozoonosis is only contagious while the parasites are in the kidneys, a three-month period. Unfortunately the owner will probably not know the rabbit has the parasite at this stage. Therefore, good sanitation practices are the best prevention. Rabbit owners with dogs, cats, hamsters, guinea pigs, or birds should be especially attentive to good sanitation practices. Always wash hands after cleaning dog feces from the yard, cat litter boxes, and bird cages. Dispose of any rabbit bedding or feed that becomes contaminated with rodent or bird feces.
- Ken Boschert, D.V.M. Internal Parasites in Rabbits
- Lucile C. Moore. A House Rabbit Primer