Diagnosing and treating common neurologic diseases in rabbits - Veterinary Medicine
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Diagnosing and treating common neurologic diseases in rabbits
To identify the source of neurologic signs in a rabbit, use the same diagnostic process as you would in a dog or cat. Here are some disorders to include in your differentials and how they can best be treated.


VETERINARY MEDICINE


CEREBROSPINAL NEMATODIASIS

Cerebrospinal nematodiasis (cerebral larval migrans), caused by Baylisascaris procyonis (the common roundworm in raccoons) or possibly Baylisascaris columnaris (the common roundworm in skunks), has been reported in rabbits and may produce severe or fatal neurologic disease.5,15 Severe encephalopathy can be caused by just a few B. procyonis larvae. Neurologic signs include ataxia, circling, opisthotonos, tremors, and torticollis.

Rabbits most commonly acquire these parasites from hay, bedding, or edible vegetation that has been contaminated by raccoon feces.5,15 Eggs remain infective for at least one year.16 After embryonated eggs (generally in hay or bedding) are ingested, larvae are released in the intestine where they begin an aggressive somatic and pulmonary migration. Central nervous system signs can be profound because of the parasites' ability to migrate to the brain, grow rapidly, and produce metabolic wastes and enzymes resulting in a severe inflammatory response.

Cerebral larva migrans should be considered in rabbits with neurologic signs that are housed outdoors and that have potentially been exposed to Baylisascaris species eggs. However, diagnosis is by postmortem histologic evaluation of the brain. Evidence of larval migration can be found in the cerebrum, cerebellum, midbrain, and medulla and includes multifocal areas of necrosis with aggregations of inflammatory cells (eosinophils, lymphocytes, plasma cells, and macrophages). The Baermann technique can be used to recover larvae from brain tissue.

Once in the brain, B. procyonis larvae cause destruction of nervous tissue that is basically nonresponsive to medical therapy. Although euthanasia is generally indicated in affected rabbits, some veterinarians have had success slowing the progression of presumptive cerebrospinal nematodiasis with oxibendazole (60 mg/kg orally every 24 hours indefinitely).5 To prevent this disease, owners should guard against fecal contamination of rabbit housing, feed, and bedding by raccoons.

TOXOPLASMOSIS

Toxoplasmosis is an uncommon cause of central nervous system disease in domestic rabbits. Neurologic signs associated with this disease include ataxia, muscle tremors, posterior paralysis, and tetraplegia. The immunoperoxidase technique used on neural tissue is probably the best test available for diagnosing toxoplasmosis.

Histologically, Toxoplasma gondii can be differentiated from E. cuniculi by its strongly positive uptake of hematoxylin stain. Toxoplasma gondii is transmitted primarily by the ingestion of oocysts in infected cat feces. Rabbits with toxoplasmosis can be treated with pyrimethamine in combination with a sulfonamide such as trimethoprim-sulfa.5 To prevent toxoplasmosis, do not expose pet rabbits to an environment that may have been contaminated with cat feces.

NUTRITIONAL DEFICIENCIES

Some neurologic diseases in rabbits have a nutritional basis. For example, nutritional muscular dystrophy in rabbits is caused by hypovitaminosis e and is characterized by degeneration and necrosis of skeletal muscle fibers.5,7,13 Because prolonged storage of feed adversely affects the vitamin e content, rabbits should only be fed fresh feed, or rabbits' diets should be supplemented with an alternative vitamin e source, such as wheat germ or leafy green vegetables. Hypovitaminosis a has also been reported to cause a neurologic disturbance in rabbits characterized by circling, convulsions, opisthotonos, and paralysis.5 Hydrocephalus has been observed in young born to vitamin a-deficient does. In addition, convulsions can occur in rabbits maintained on a diet deficient in magnesium. Prevent these nutritional disorders by making sure owners feed pet rabbits only a fresh, high-quality diet.

LEAD POISONING

Lead poisoning in rabbits may be characterized by subtle neurologic signs, depression, reduced appetite, and lethargy.5,13 In later stages, more severe neurologic signs (ataxia, seizures) may be noted. Rabbits can be exposed to this poisoning because of their tendency to gnaw on almost anything they can find, including walls with old paint, toys, drapery weights, linoleum, and golf balls, some of which contain lead. This exposure most commonly occurs in rabbits that are free-roaming in the house, garage, or garden.

Diagnosis includes evaluating abdominal radiographs for gastrointestinal metallic densities and obtaining blood lead concentrations. Blood lead concentrations > 10 g/dl and clinical signs of plumbism are diagnostic for lead toxicosis.5 The treatment of choice is chelation with edetate calcium disodium (Ca EDTA) (Calcium Disodium Versenate—3M) at a dosage of 25 mg/kg given subcutaneously every six hours for five days.5,11 Two courses of treatment one week apart may be required.


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Source: VETERINARY MEDICINE,
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