If you notice that your rabbit has a head tilt, is walking crooked or clumsy, has a noticeable eye problem, has any sort of neurologic symptom such as severe weakness or seizures, or urinary issues, they may be showing signs of an infectious disease called Encephalitozoon cuniculi. This document will help you to understand what that means for you and your pet rabbit.
E. cuniculi or ECUN) is a single-celled parasite that commonly infects pet rabbits but doesn’t always cause clinical disease. Infection occurs by exposure to infected urine and feces or in utero (prior to being born while still in the mother’s uterus). After initial infection, E. cuniculi replicates in the lung, liver and kidney. Over time, it can spread to the central nervous system, and to the lens of the eye, especially in those rabbits infected in utero. Symptoms may occur at any point in life, regardless of how and when they were infected.
Because E. cuniculi infects various organs throughout the body, clinical signs (symptoms) can vary. Neurologic signs can include abnormal eye movements, seizures, paralysis, or vestibular disease (balance issues, head tilt) are most common. Kidney disease may manifest as increased drinking and urination, urine scald, and/or weight loss. E. cuniculi infection can also be associated with eye disease, including cataracts, uveitis, and other intraocular changes. Depending on the clinical signs, it is important to consider other differentials, or other disease possibilities. For example, a rabbit with a head tilt could have ear disease and not E. cuniculi.
If a rabbit has any of these clinical signs suggestive of E. cuniculi, diagnostic tests are recommended. Baseline bloodwork evaluates internal organ function (including kidney function) and white and red blood cell counts. A test for E. cuniculi may also be recommended to screen the blood for E. cuniculi-specific antibodies (to show that the body is reacting to the parasite). Whole body x-rays may be recommended to further evaluate the internal organs. One complication of screening the blood for antibodies is that clinically normal (healthy) rabbits can have elevated antibody titers, but may not suffer from obvious illness. This means that at some point the rabbit was exposed to the parasite, but is not actively sick from it.
If E. cuniculi is diagnosed, treatment may consist of an oral anti-parasite medication, most commonly fenbendazole or albendazole. Other treatments may also be advised, such as supportive care if the rabbit is not eating normally on its own, anti-inflammatory therapy, and/or anti-vertigo medicine. Treatment is usually effective but E. cuniculi will never be completely eliminated from the body.
E. cuniculi also has zoonotic (able to be transmitted from animal to humans) potential, particularly in people that are significantly immunocompromised such as transplant recipients, those infected with HIV, children, and the elderly. While this is extremely rare, it is important that families are aware of this possibility.