Coccidiosis
Coccidiosis is a common and worldwide protozoal disease of rabbits. Rabbits that recover frequently become carriers. There are two 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.
Hepatic Coccidiosis in Rabbits
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 not make normal gains. Infrequently, death may follow a short course. Rabbits usually succumb within 1 month 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, whereas 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. It is important not to confuse the oocysts with the normal yeast (Cyniclomyces guttulatus), which is commonly seen in fecal examinations.
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 days. A single oral dose of sulfadimethoxine at 50 mg/kg, followed by its inclusion in drinking water at 1 g/4 L for 9 days, was found to significantly reduce fecal oocyst count. 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 coccidiostats that may prove to be effective include amprolium (9.6% in water or 0.5 mL/500 mL), salinomycin, diclazuril, and toltrazuril/ponazuril. A single oral dose of toltrazuril at 2.5 mg/kg or 5 mg/kg has also significantly reduced oocyst count. Treatment is best administered for a minimum of 5 days and repeated after 5 days. Rabbits 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.
Intestinal Coccidiosis in Rabbits
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 Cyniclomyces guttulatus that can also be found in large numbers. Treatment is similar to that for hepatic coccidiosis except that sulfaquinoxaline 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 two 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. Note a pet rabbit can become infected with Tenia sp by eating hay contaminated with fecal matter of infected animals; no direct contact with a dog is needed. 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. 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 weight, fail to produce, and suffer secondary infections, which may damage the inner ear, reach the CNS, and result in torticollis. The brown crumbly exudate should never be removed in a conscious rabbit, because this is very painful. The crusts will slowly slough off as the mites die and the tissue underneath heals. The incidence is much lower when rabbits are housed in wire cages instead of solid cages. The mite is readily transmitted by direct contact. Rabbits should be treated systemically with any of the miticides approved for use in dogs and cats. A variety of injectable ivermectin treatment regimens effective against both fur and ear mites have been reported, with the dosage of ivermectin 200–400 mcg/kg, SC, two or three treatments 10–21 days apart. Mites may also be treated with selamectin (20 mg topically every 7 days has been effective).
Courtesy of Dr. Joerg Mayer.
Fur mite infestations are common, and two 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 one 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 people, especially on the arms. Weekly dusting of animals and bedding with permethrin powder can control Cheyletiella mites.
Courtesy of Dr. Louise Bauck.
Rabbits are rarely infested with either Sarcoptes scabiei or Notoedres cati. These mites burrow into the skin and lay eggs. The rabbits are extremely pruritic, and the parasites are difficult to eliminate on domestic rabbits. The condition is extremely contagious and can be transmitted to people.
Fleas of the Ctenocephalides felis, C canis, and Pulex irritans species can affect rabbits and many other animals. Imidacloprid is a flea adulticide; the feline dose should be divided in two or three spots to treat rabbits infested with fleas. Fipronil is contraindicated for use in rabbits because of potential toxicity. Flea collars are also not recommended. It is important to also treat every cat and dog in the house, because the original host is not usually the rabbit.
Encephalitozoonosis
Encephalitozoon cuniculi is considered a primitive fungal infection of rabbits and occasionally of mice, guinea pigs, rats, and dogs. Encephalitozoonosis is a widespread disease in rabbits, with reports of infection found in 50%–75% of pet rabbit in various countries. The animal can get infected in utero or by ingesting the spores, which are shed via the urine of affected animals. Spores can be found in the urine 1 month after infection and are excreted in large numbers up to 2 months after infection. The spores can survive in the environment for up to 6 weeks at 72° F (22° C). Shedding of spores by the affected animal through the urine lasts for 3 months. Intermittent shedding of small amounts of spores in the urine by the infected rabbit afterwards makes diagnosis of current infection by identifying spores in urine unreliable.
Clinical Signs of Encephalitozoonosis in Rabbits
Courtesy of Dr. Joerg Mayer.
E cuniculi has a predilection for migration to the following organs: kidney, CNS, and lens (following in utero infection). These are the main tissues involved in the manifestation of the clinical signs. The spores invade the cells of the affected organ and eventually form cysts, which then overcrowd and rupture the cell, resulting in spore release. This cell rupture is associated with a severe inflammatory response, causing either neurologic, renal, or ophthalmologic signs. Immunocompetent rabbits can develop chronic, subclinical infections in a balanced host-parasite relationship, associated with granulomatous lesions primarily affecting the target organs mentioned above.
Some affected rabbits develop CNS 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, because both infections are common and can occur together. Urinary incontinence can be observed when the kidneys are affected during the acute phase of the disease. Other clinical signs can include polydipsia, polyuria, inappetence, weight loss, lethargy, and dehydration.
Lesions
At necropsy, the most significant macroscopic lesion is pitting of the kidneys. Microscopic lesions consist of focal granulomas and pseudocysts in the brain and kidneys.
Phacoclastic uveitis is the key clinical signs for manifestation of E cuniculi in the eye. Cataract formation and the development of white intraocular masses and uveitis are often seen close to the anterior lens capsule.
Diagnosis of Encephalitozoonosis in Rabbits
Courtesy of Dr. Tracy Bartick.
Courtesy of Dr. Tracy Bartick.
Because many rabbits have chronic, asymptomatic infections, an accurate and direct diagnosis of encephalitozoonosis in rabbits can be problematic. Diagnosis is made by histologically identifying the lesions (pseudocysts) and observing the organisms when stained with Giemsa, Gram, or Goodpasture carbol fuchsin stains. The causative agent is extremely small, and identification on light microscopy can be challenging. Thus, serology is considered a reliable diagnostic tool for the confirmation of E cuniculiinfections in the clinical setting. Clinical correlations have been demonstrated between serologic testing and histopathology. Different assays from multiple commercial laboratories exist, and all provide indirect evidence of an infection. It is important to pick one laboratory and one reliable method when performing repeated testing, to evaluate the progression of the treatment or the disease. A commonly used test measures IgG and IgM antibodies against E cuniculi and correlates their level with C reactive protein. Other acceptable methods include IFAT (indirect fluorescence antibody test), ELISA, and CIA (carbon immunoassay).
Treatment of Encephalitozoonosis in Rabbits
No uniformly effective treatment has been established. Some evidence suggests that oxibendazole or albendazole (20–30 mg/kg/day, PO, for 7–14 days, then 15 mg/kg/day, PO, for 30–60 days) or fenbendazole (20 mg/kg/day, PO, for 28 days) may be effective in vivo. The treatment of choice generally is fenbendazole, because it has been shown to both prevent and treat E cuniculi infections. In addition, it has been shown that oral administration of fenbendazole before an experimental infection protected rabbits against infection with E cuniculi. Client education is important when dispensing benzimidazoles because adverse reactions as severe as bone marrow aplasia (radiomimetic lesion) have been reported with the use of benzimidazoles in rabbits at high doses. Thus, owners need to strictly adhere to the recommended dosages and treatment intervals, and it is important to consider monitoring CBCs during treatment, especially if clinical signs persist.
The use of steroids in rabbits is controversial, but they have been used in select cases without causing any detrimental effects (ie, severe immune suppression). If clinical signs are acute (< 48 hours) and are due to an inflammatory condition of the CNS, one dose of a steroid (dexamethasone, 0.5 mg/kg, IM, once) may decrease the acute inflammation. Prevention entails good sanitation and possibly serologic screening of breeding stock with elimination of positive reactors. A differential diagnosis in rabbits with outdoor access is an aberrant migration of Baylisascaris spp into the nervous system.
Encephalitozoonosis is an emerging disease of immunodeficient people.
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. Avermectin at regularly used dosages should be an effective treatment. Unless infestation is severe, treatment might not be warranted, however, because pinworms often cause no clinical signs. Rabbit pinworms are not transmissible to people.
