Parasites in rabbits

Encephalitozoon cuniculi

• Encephalitozoon cuniculi is an obligatory intracellular primitive fungus that can infect a wide range of mammals, including rodents, rabbits, horses, carnivores and humans, in which the organism is known as an opportunistic pathogen of immunocompromised individuals.
• This parasite may be transmitted in body exudates or trans-placentally.
• The infective form of microsporidia is a resistant spore which can survive for a long time in the environment.
• Approximately one month after the rabbit is infected it begins to shed E. cuniculi spores via its urine.
• Spores continue to be shed for approximately 3 months, but can be shed throughout the rabbit’s life
• Most often, E. cuniculi remains dormant within rabbits, never causing any problems upon initial infection.
• On occasions E. cuniculi reaches nervous tissue, rabbits can experience neurological impairment, characterized by partial or complete paralysis, loss of coordination, seizures, and head tilting.
• As the central nervous system, the kidney and the eye are predilection organs for the organism, predominant histopathological alterations comprise granulomatous meningoencephalitis, chronical interstitial nephritis and phacoclastic uveitis.
• A definitive diagnosis of encephalitozoonosis in vivo is difficult, but it is important for specific treatment and the determination of possible zoonotic risks
• Antibodies to E. cuniculi can be detected through serology (a blood test).
• A rabbit who has been exposed to E. cuniculi will produce antibodies as a result of this exposure.
• Seroprevalence rates are usually high in pet rabbit populations with 37% to 68% of the population.
• A positive titer tells you that the rabbit has been exposed to this parasite at some point in its life.
• Note that this does not allow one to differentiate between simple exposure and an active infection.

The diagnosis

• A tentative clinical diagnosis is usually obtained by a combination of clinical, neurological and ophthalmological examinations, serological tests and by the exclusion of differential diagnosis.
• Otitis media/interna is the main differential diagnosis for rabbits showing vestibular signs.

Clinical signs

• As lesions are caused within the central nervous system, kidney or eye, rabbits suffering from encephalitozoonosis may demonstrate neurological symptoms, signs of kidney failure or phacoclastic uveitis.
  - Nystagmus
  - Otitis

Treatment

• Rabbits that were infected experimentally during their oral treatment with fenbendazole (20 mg/kg/day) did not seroconvert, and spores could not be isolated from their brain tissue. 
• Avoid overdose. Bone marrow lesions are reported in rabbits which received regular doses but many were overdosed. 
• Cases are usually fatal

Zoonotic potential

• While the disease has a zoonotic potential, the vast majority of human cases are in severely immune compromised individuals.
• Often the infections are traced back to dogs.

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