THE MERCK VETERINARY MANUAL
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Parasitic Diseases of Rabbits

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Coccidiosis

Coccidiosis is a common and worldwide protozoal disease of rabbits. Rabbits that recover frequently become carriers. There are 2 anatomic forms: hepatic, caused by Eimeria stiedae, and intestinal, caused by E magna, E irresidua, E media, E perforans, E flavescens, E intestinalis, or other Eimeria spp. Transmission of both the hepatic and intestinal forms is by ingestion of the sporulated oocysts, usually in contaminated feed or water.

Severity of disease depends on the number of oocysts ingested. Young rabbits are most susceptible. Affected rabbits may be anorectic and have a rough coat. Hepatic coccidiosis is most often subclinical, but growing rabbits may fail to make normal gains. Infrequently, death may follow a short course. Rabbits usually succumb within 1 mo after a severe experimental exposure. At necropsy, small, yellowish white nodules are found throughout the hepatic parenchyma. In the early stages, they may be sharply demarcated, while in the later stages they coalesce. The early lesions have a milky content; older lesions may have a more cheese-like consistency. Microscopically, the nodules are composed of hypertrophied bile ducts or gallbladder. Diagnosis of this form of coccidiosis is based on the gross and microscopic changes, along with demonstration of the oocysts in the bile ducts. An impression smear of a lesion in the liver examined under light microscopy often reveals oocysts. The oocysts may also be demonstrated by fecal flotation.

Treatment is difficult, and control rather than cure is expected. Sulfaquinoxaline administered continuously in the drinking water (0.04% for 30 days) prevents clinical signs of hepatic coccidiosis in rabbits heavily exposed to E stiedae. However, it may not prevent the lesions. Sulfaquinoxaline may also be given in the feed at 0.025% for 20 days, or for 2 days out of every 8 until marketing. Because feed-grade sulfaquinoxaline can be difficult to obtain, liquid sulfaquinoxaline is used more commonly. Withdrawal time is 10 days for rabbits used for food. Other coccidiosis treatments do not have approved withdrawal times for meat rabbits. Other sulfa drug treatments include sulfadimethoxine (0.5–0.7 g/L drinking water) and sulfadimerazine (2 g/L drinking water). Other coccidiostats that may prove to be effective include amprolium (9.6% in water or 0.5 mL/500 mL), salinomycin, diclazuril, and toltrazuril. Treatment is best administered for a minimum of 5 days and repeated after 5 days. Rabbits that are treated successfully are immune to subsequent infections.

Treatment will not be successful unless a sanitation program is instituted simultaneously. Elimination of fecal-oral transmission of infective oocysts is achieved by preventing feed hoppers and water crocks from becoming contaminated with feces. Hutches should be kept dry and the accumulated feces removed frequently. Wire cage bottoms should be brushed daily with a wire brush to help break the life cycle of the protozoa. Ammonia (10%) solution is lethal to oocysts and is the best choice to disinfect cages or ancillary equipment exposed to fecal material.

This form of coccidiosis can occur in rabbits receiving the best of care, as well as in rabbits raised under unsanitary conditions. Typically, infections are mild and often no clinical signs are seen. In early infections, there are few lesions; later, the intestine may be thickened and pale. Good sanitation programs that can eliminate hepatic coccidiosis do not seem to eliminate intestinal coccidiosis. Intestinal coccidiosis is generally diagnosed by fecal flotation and microscopic identification of the oocysts (species). It is important to distinguish coccidian oocysts from the nonpathogenic yeast Saccharomycopsis guttulatus that can also be found in large numbers. Treatment is similar to that for hepatic coccidiosis except that sulfaquin-oxaline is given for 7 days and repeated after a 7-day interval.

Larval Worm Infection

Although adult tapeworm infections are rare in domestic rabbits, the discovery of larval tapeworm cysts on the serosal peritoneum is common. Rabbits are intermediate hosts for 2 species of canine tapeworm, Taenia serialis and T pisiformis. Although T serialis is rare in domestic rabbits, it is somewhat more common in wild ones. The larval stage of T pisiformis, a cysticercus, is found attached to the mesenteries. Before forming these fluid-filled cysts, the young larvae migrate through the liver, where they leave white, tortuous subcapsular tracts. Generally, there are no clinical signs, and diagnosis occurs at necropsy. Treatment is usually not attempted, but control is accomplished by restricting access of dogs (the final host of the tapeworm) to the area in which food and nesting material are stored. Dogs should not be fed infected dead rabbits because this perpetuates the cycle. Mebendazole at 1 g/kg of feed (50 mg/kg) for 14 days is reported to be an effective treatment.

Baylisascaris procyonis has been reported in rabbits. Signs are similar to those induced by Encephalitozoon cuniculi. No treatment is available.

Ectoparasites

The ear mite Psoroptes cuniculi is a common parasite of rabbits worldwide. Mites irritate the lining of the ear and cause serum and thick brown crusts to accumulate, creating an “ear canker.” Infested rabbits scratch at and shake their head and ears. They lose flesh, fail to produce, and suffer secondary infections, which may damage the inner ear, reach the CNS, and result in torticollis. With the rabbit well restrained or under general anesthesia, the brown crumbly exudate should be removed with cotton soaked in dilute hydrogen peroxide. The ear should be treated with any of the miticides approved for use in dogs and cats. Those products containing a cerumenolytic agent are particularly useful in removing the heavy, crusted material. The medication should be applied within the ear and down the side of the head and neck. The incidence is much lower when rabbits are housed in wire cages instead of solid cages. The mite is readily transmitted by direct contact. A variety of injectable ivermectin treatment regimes effective against both fur and ear mites have been reported, with the dosage of ivermectin 200–400 μg/kg, SC, 2–3 treatments 10–21 days apart. Mites may also be treated with selamectin (6 mg or 18 mg topically has been shown to be effective).

Fur mite infestations are common, and 2 genera, Cheyletiella and Listrophorus, are found worldwide. A number of different species of the genus Cheyletiella are found on rabbits. The most common in North America is C parasitovorax. The genus Listrophorus has but 1 species, L gibbus. These mites live on the surface of the skin and do not cause the intense pruritus seen with sarcoptic mange. Fur mite infestations usually are asymptomatic unless the rabbit becomes debilitated. Cheyletiella may be noticed as “dandruff.” Scraping the dandruff onto a dark paper or background will demonstrate the “walking dandruff,” as Cheyletiella is called. Transmission is by direct contact. Diagnosis is accomplished by skin scraping and light microscopy. Cheyletiella mites may cause a mild dermatitis in humans. Weekly dusting of animals and bedding with permethrin powder can control Cheyletiella mites.

Rabbits are rarely infested with either Sarcoptes scabei or Notoedres cati. These mites burrow into the skin and lay eggs. The rabbits are extremely pruritic and it is difficult to eliminate the parasites on domestic rabbits. The condition is extremely contagious and can be transmitted to humans.

Fleas of the Ctenocephalides felis, C canis, and Pulex irritans species can affect rabbits and many other animals. Imidacloprid is a flea adulticide that kills on contact; the feline dose should be divided in 2–3 spots to treat rabbits infested with fleas. Fipronil is contraindicated for use in rabbits due to potential toxicity. Flea collars are also not recommended.

Encephalitozoonosis

(Nosematosis)

Encephalitozoon cuniculi is a widespread protozoal (microsporidian) infection of rabbits and occasionally of mice, guinea pigs, rats, and dogs. Usually, no clinical signs are seen, but a few rabbits develop mild, chronic renal disease. Some develop brain lesions that may result in convulsions, tremors, or head tilt. Head tilt is often caused by bacterial infection with Pasteurella multocida; this can be difficult to distinguish from head tilt associated with E cuniculi infection as both infections are common and can occur together. The mode of transmission is not definitely known, but the organism is shed in the urine. It seems to be mildly contagious in a rabbitry. At necropsy, the most significant lesion is pitting of the kidneys. Microscopic lesions consist of focal granulomas and pseudocysts in the brain and kidneys. Sometimes a severe, focal, interstitial nephritis is seen. Diagnosis is made by histologically identifying the lesions (pseudocysts) and observing the organisms when stained with Giemsa, Gram's or Goodpasture-carbol fuchsin stains. Several serologic and skin tests are helpful in screening rabbits for antibodies to the organism, but positive serology only indicates past infection and does not confirm a diagnosis. Effective treatment has not been established. Anecdotal evidence suggests that oxibendazole or albendazole (20–30 mg/kg, PO, sid for 7–14 days, then 15 mg/kg, PO, sid for 30–60 days) or fenbendazole (20 mg/kg, PO, sid for 5–28 days) may be effective. Prevention entails good sanitation and, possibly, serologic screening of breeding stock with elimination of positive reactors. A differential diagnosis is an aberrant migration of Baylisascaris spp into the nervous system. Encephalitozoonosis is an emerging disease of immu-nodeficient humans.

Pinworms

Passalurus ambiguus, the rabbit pinworm, usually is not clinically significant but often is upsetting to owners. It is common in many rabbitries and is distributed worldwide. Transmission is by ingestion of contaminated food or water. The adult worm lives in the cecum or anterior colon. Diagnosis is made by observing the adults at necropsy or by finding the eggs during examination of the feces. Single treatments are not very effective because the life cycle is direct and reinfection is common. Piperazine citrates in the water (3 g/L) for alternating 2-wk periods or fenbendazole (50 ppm in feed for 5 days) are effective treatments. Rabbit pinworms are not transmissible to humans.

Last full review/revision July 2011 by Diane McClure, DVM, PhD, DACLAM

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