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Case Study: Encephalitozoan Cuniculi Infection


Bugsy was a fit and healthy 18 month old house rabbit, who spent time grazing outside. His owner noted that he had become quieter than usual and had not eaten or drunk, was falling over and appeared to be unable to see with his right eye.

Bugsy was diagnosed with bilateral cataracts (clouding of the lens of the eye) with only partial vision in the left eye but sadly no vision in the right eye. Bugsy also had a head tremor most likely the result of an infection with a protozoan parasite called Encephalitozoan Cuniculi.

Rabbits can be infected at a very young age by ingesting urine contaminated by E. cuniculi spores, from other rabbits including their own mother. In turn these new infected rabbits then may shed spores on or off for life. The parasite settles in the body organs such as the liver, kidneys, heart and brain where it is then walled off causing lesions called "granulomas".

Some infected rabbits go through life quite happily without experiencing any problems from their E. cuniculi infection. However other rabbits will encounter problems as a result of infection. Kidney granulomas are usually harmless, although a few rabbits develop chronic kidney failure. Lesions in the brain tend to cause neurological problems, such as fits, tremors, head tilt, wobbly hind limbs, and loss of balance, urinary incontinence and coma. Unborn rabbits may become infected via the placenta, in which case granulomas may develop around the lens of the eye causing loss of sight as in Bugsy’s case.

Diagnosis is usually made on clinical grounds and with a confirmatory blood test, but in many cases we start treatment just based on symptoms. The mainstay treatment is a drug called fenbendazole (Panacur™, produced by Intervet) for 28 days. Other supportive therapy may also be needed.

Happily Bugsy’s neurological signs resolved and he appeared to regain the sight in his eyes.

Fenbendazole can also be used to prevent the infection if used routinely. E. cuniculi has been one of the hottest topics in rabbit health over the past few years. It's also one of the most controversial! Fortunately knowledge on the subject is increasing all the time so it is an interesting area to keep updated about.

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