PARASITIC DISEASES
I. Coccidiosis
II. Encephalitozoonosis
III. Passalurus ambiguus
IV. Baylisascaris procyonis
V. Cestodes
VI. Mites
VII. Fleas and Lice
VIII. Cuterebra Infestation

I. Coccidiosis
A. Hepatic Coccidia
1. Etiology: Eimeria stiedae
2. Transmission: Ingestion of sporulated oocysts (unsporulated in freshly voided feces) is the mode of transmission. The incidence of infection is moderate to high.
3. Pathogenesis: Eimeria stiedae excysts in the duodenum, travels to the liver via the bloodstream or lymphatics, and invades epithelial cells of bile ducts to begin schizogeny.
4. Clinical Signs: Signs predominate in young rabbits and may include anorexia, debilitation, and pendulous abdomen with hepatomegaly noted on abdominal palpation. Mortality is low except in young rabbits.
5. Pathology: An enlarged liver with multifocal, flat, yellow-white lesions containing yellow exudate and occasionally a distended gallbladder that contains bile may be seen at necropsy (A.). The pathognomonic microscopic lesion is marked periportal fibrosis surrounding enlarged bile ducts lined with hyperplastic bile duct epithelium that harbors inflammatory cell infiltrates, and E. stiedae macrogametes, microgametocytes and oocysts.

7. Diagnosis: An antemortem diagnosis can be made by examination of feces by direct smear, flotation or concentration/flotation methods. It can be difficult to identify E. steidae oocysts in fecal specimens since they may not be readily shed in the bile. On necropsy, the recognition of the flat liver lesions and identification of oocysts in the bile provide diagnostic information. The histological appearance of liver with identification of intraepithelial coccidial organisms will allow diagnosis from tissue biopsies.
8. Treatment: Drugs approved as coccidiostats for rabbits used for meat in US include sulfamerazine (0.02% in water), sulfaquinoxaline (0.05% in water or 0.03% in feed), sulfamethoxine (75 mg/kg BW in feed), and lasalocid (68-113 gms per ton of feed). Hepatic coccidia are difficult to eliminate with anticoccidial therapy, and lasalocid has been the most successful of the listed drugs in treating hepatic coccidiosis.
9. Control: Rabbits should be housed on wire-meshed floors. Bottoms of cages are to be brushed daily to remove adherent feces, and cleaned and disinfected regularly (1% chlorox). Weanlings should be raised separate from adults. Feeding fresh greens or hay will prevent use of forage that may be contaminated with droppings from wild rabbits.
B. Intestinal Coccidia
1. Etiology: Eimeria magna, Eimeria irresidua, Eimeria perforans, and Eimeria media are frequently observed pathogenic species. All species infect the intestinal tract and replicate in the absorptive epithelium of the mucosa.
2. Transmission: Transmission occurs by ingestion of sporulated oocysts. Incidence of infection is high.
3. Clinical Signs: Signs vary and are most severe in young rabbits. Poor weight gain, diarrhea ranging from mucoid to watery to hemorrhagic, polydipsia and sometimes acute death are seen. Older rabbits may shed coccidial oocysts without expression of clinical disease.
4. Gross Pathology: Fluid intestinal contents are often observed in heavily parasitized rabbits. One may see multiple white patches or ulcers on mucosal surface of the small or large intestine.
5. Diagnosis: Antemortem diagnosis can be made by examination of feces by direct smear, flotation or concentration/flotation methods. A postmortem diagnosis can be made on examination of mucosal scrapings and by observation of coccidial organisms on histological sections of intestine.

D. Treatment: As mentioned in the above section, drugs approved as coccidiostats for rabbits used for meat in US include sulfamerazine (0.02% in water), sulfaquinoxaline (0.05% in water or 0.03% in feed), sulfamethoxine (75 mg/kg BW in feed), and lasalocid (68-113 gms per ton of feed) have been provided in schedules of 3-weeks-on / 3-weeks-off periods.
E. Control: Rabbits should be housed on wire-meshed floors. Bottoms of cages are to be brushed daily to remove adherent feces, and cleaned and disinfected regularly (1% chlorox). Weanlings should be raised separately from adults. Feeding fresh greens or hay will prevent use of forage that may be contaminated with droppings from wild rabbits.
II. Encephalitozoonosis
A. Etiology: Encephalitozoon cuniculi (once called Nosema cuniculi) is a microsporidian parasite, 2.5 x 1.5 micrometers (oval) with thick wall.
B. Transmission: E. cuniculi is shed in the urine and has been experimentally transmitted by direct contact (ingestion, aerosol).
C. Clinical Signs: Usually there are no clinical signs (latent infection); however, in heavy infections there may be torticollis, convulsions, tremors, posterior paresis, and edema.
D. Pathology: In acute cases the kidneys are swollen. Chronic lesions are more commonly seen and include multifocal, pinpoint, white, pitted areas on the surface of the kidneys. Histological examination of kidneys and brain will reveal a granulomatous interstitial reaction with fibrosis in the kidney and focal granulomas in the brain (white arrow) with perivascular plasma cell cuffs and nonsuppurative meningitis. The organism may be found in renal tubular epithelial cells or in microglia in the brain. Encephalitozoon stains poorly with hematoxylin and eosin stains, but is Gram-positive (black arrow) and refractile when viewed with polarized light.

E. Diagnosis: Diagnosis is provided by histopathologic demonstration of organisms and serologic detection of antibody via ELISA and indirect fluorescent antibody tests. Most research animal diagnostic laboratories offer an ELISA or FA test.
F. Treatment and Control: No treatment is effective. Control is difficult in colonies, especially breeding colonies. Housing rabbits on wire and placing the cages away from contact with walls and in single rows (no stacking) may prevent cage-to-cage urine contamination. Rabbits will seroconvert 30 days prior to shedding sporocysts in urine, so a strict program of culling seropositive rabbits can be instituted based on results of serologic screening every 2 weeks.
Public Health Significance: Encephalitozoon cuniculi has been diagnosed in immunosuppressed humans. The direct association between rabbit ownership and infection has not been documented.
III. Passalurus ambiguus
The rabbit pinworm does not cause clinical disease in infected rabbits. The rabbit pinworm has a direct life cycle and adult pinworms reside in the cecum and large intestine. The males are 4.1 mm long, 300 mm in diameter with a single curved spicule. The females 6.6 mm long with long tail posterior to vulva (see photo).
The eggs are flattened on one side. Treatment with piperazine adipate (0.5 gm/kg to 0.75 gm/kg s.i.d. for 2 days in food or water) is effective. Ivermectin at 0.2 mg/kg is most likely effective. Control of infection is aimed at preventing ingestion of contaminated feces.
IV. Baylisascaris procyonis
Infection of rabbits with the raccoon ascarid, Baylisascaris procyonis, occurs by ingestion of bedding or hay contaminated with raccoon feces. Reports of this nematode as a rabbit pathogen are increasing. Clinically infected rabbits display torticollis, ataxia, tremors, and falling (loss of balance). At necropsy, multiple, white raised nodules in the epicardium, endocardium and serosal surface of the liver may be seen. Larval granulomas and multifocal necrosis in the cerebrum and cerebellum, and larval granulomas and tracks in the viscera are typical histologic lesions. Cross sections of larvae with cuticular alae are often visualized in brain sections. Diagnosis is made from clinical signs and the presence of larvae in histosections. Treatment has not been attempted. Efforts to prevent infection include use of clean bedding and hay.
V. Cestodes
Wild rabbits are definitive and intermediate hosts for a number of tapeworms. The life cycles of these parasites practically precludes infection of domestic or laboratory rabbits. Taenia pisiformis infections are very common in wild rabbits and are found occasionally in domestic rabbits. The stage found in rabbits is a cysticercus. Most cysticerci are found in the liver or attached to the mesentery and cause little damage. A second taenid found in rabbits is T. serialis. The stage of the cestode seen in rabbits is a coenurus which occurs in connective tissue of muscle. Infection in wild rabbits is less common than T. pisiformis and is extremely rare in domestic rabbits. The dog is the definitive host of both cestodes.
VI. Mites
A. Psoroptes cuniculi - ear mite
1. Etiology: This nonburrowing, obligate mite has a high incidence of occurrence in meat, laboratory and pet rabbits. The life cycle is completed in around 21 days.
2. Clinical Signs: Scratching at ears with hind feet and the presence of crusty exudate in the pinnas with an underlying moist dermatitis are characteristic. The parasites do not cause otitis media since they do not penetrate the tympanic membrane.
3. Diagnosis: Mites can be observed with an otoscope or on a mineral oil preparation of the crusty exudate. The mites are oval-shaped with well-developed legs, pointed pedicles, and bell-shaped suckers on the end of pedicles.
4. Treatment: Crusts are gently removed from the canal. Mineral oil with or without acaricide in the ear canal will kill the mites. Ivermectin at doses of 0.2 to 0.4 mg/kg SC will eliminate most infections with a single treatment. Antibiotic cream can be used if the ear is infected.
5. Control: Infected animals should be isolated. During treatment, the cage should be disinfected.
B. Cheyletiella parasitovorax - fur mite
1. Etiology: C. parasitovorax is a small, noninvasive mite, with a low to moderate incidence of infection.
2. Clinical Signs: Partial alopecia of dorsal trunk or scapular region with a fine, grey scale on erythematous skin results from infestation. (The mite is often called "walking dandruff.") There is some pruritis.
3. Diagnosis: Examination of the pelt will reveal small white mites with piercing chelicerae and large curved palpal hooks, and the eggs are attached to hair shafts.
4. Treatment: Rabbits can be dusted or sprayed with pyrethrin preparations or silica gel acaricides, with repeat treatments at 10 day intervals. Ivermectin at 0.2 to 0.4 mg/kg SC should also be effective.
5. Control: Infested rabbits should be isolated during treatments. Cleaning and spraying the rabbit's environment with insecticidal preparations aids in decontamination of the fomites.
Public Health Significance: This parasite can cause a transient pruritic rash in hypersensitized people, especially children.
C. Listrophorus gibbus - fur mite
1. Etiology: L. gibbus is a small, nonburrowing mite present at low to moderate incidence in domestic rabbits. It is an obligate parasite, completing all stages of the life cycle on the host.
2. Clinical Signs: This mite is currently considered non-pathogenic and is found primarily on the back and abdomen.
3. Diagnosis: The hair shafts can be examined under a dissecting microscope or with hand lens for the characteristic brown mite or its nits.

4. Control: Isolate infected animals. Topical acaricides and ivermectin as described for cheyletiella are thought to be effective in treatment.
VII. Fleas and Lice
Rabbits are commonly infested with Ctenocephalides sp., especially C. felis. The infestation may be asymptomatic, but may induce mild pruritis and alopecia. Rabbits can be dusted and sprayed with pyrethrin products. Do not use the flea product Frontline in rabbits since rabbit deaths have been associated with its use. The environment should be treated to control this parasitism.
Haemodipsus ventricosis (Blood Sucking Louse). The anapleurid louse is rarely found on domestic rabbits. Weakness, anemia, ruffled fur and pruritis (secondary dermatitis) are common signs of infection. The pelt can be examined with a dissecting microscope or a hand lens. Nits, as well as the adult anopleurid louse (head narrower than body), may be found on the hair. Rabbits should be treated with pyrethrin products, silica gel acaricides or ivermectin (0.2 to 0.4 mg/kg SubQ) at 10 day intervals for 2 treatments. This louse spends its entire life cycle on the rabbit with little horizontal transmission. Isolation is an effective means of control while treating the infected rabbit.
VIII. Cuterebra Infestation
Cuterebrid flies are also known as rodent and rabbit warble flies. Cuterebriasis occurs most frequently in wild rabbits, but may occur in domestic rabbits housed outdoors. Incidence peaks in the summer and late fall. Single or multiple large subcutaneous swellings containing encysted larvae with a fistula in the center are the characteristic lesions (left photo). When the larval fly is ready to pupate, it leaves the swelling and drops to the ground (right photo). Secondary bacterial infections may complicate the disease. These lesions are treated by removing the larva (without crushing it) and flushing the wound, or by surgical resection of the wound. Prevention of infestation includes moving the cage indoors, or by surrounding the hutch with screen to prevent fly exposure.