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Encephalitzoon cuniculi is a parasite most often associated with neurologic disease in pet rabbits. It can also have other manifestations including renal and ocular.

Black rabbitWhat are the signs?

The most common signs we see with affected rabbits include head tilt, rolling, and trouble walking (ataxia). The less common manifestations of the disease include a renal form of the disease where your rabbit may have an increase in thirst and/or incontinence, and an ocular form that is most commonly associated with cataracts.

How can my pet get it?

Most rabbits are infected from the urine of infected rabbits. This transmission can occur within six weeks of birth. It is also possible for an infected mother to infect her kits in utero. 

It is important to know that E cuniculi is a zoonotic disease, meaning humans can be infected with this parasite. The people most commonly affected are immunocompromised. Be sure to wash your hands and clean around your rabbit well.

The spores, or the infective form of the parasite, can be ingested or inhaled. Infected animals can start excreting spores in the urine one month after infection and these spores are then excreted in large numbers for up to two months post infection. After three months the shedding of the spores is stopped. The spores can live in the environment for up to six weeks at room temperature. Most common disinfectants are effective at inactivating the spores.

After infection the parasite initial targets organs with high blood flow like the lungs, liver, and kidneys. It is not until later in the infection that the nervous tissue is affected. The parasite multiples in the host cells which eventually leads to cell rupture. The cell death and rupture are what causes the chronic inflammation associated with the disease leading to the clinical signs.

As the parasite spreads to different tissue, the rabbit develops antibodies. This is what limits the tissue damage and spore excretion. A healthy immune system prevents the organism from multiplying but the spores remain viable for years. If later in life the rabbit is immunocompromised, these spores can then lead to disease.

How can we test for it?

Diagnosing E cuniculi infection is difficult. At this point in time there is no definitive ante mortem (live) test. Most diagnosis are made based on clinical signs and serology(the scientific study of serum and other bodily fluids). Serology tests for antibodies to the E cnniculi parasite.

Serology is helpful but not definitive. This is due to the fact that most rabbits that have been infected will have a positive titer whether or not they have an active infection. Although it has been found that most rabbits suspected of having E cuniculi will have a positive titer.

Other testing performed on E cuniculi-suspected rabbits include skull radiographs, complete blood count, and biochemistry analysis. These tests are used to help determine if there is any underlying disease or any other abnormalities that need to be addressed. These test also help rule of other causes for the clinical signs.

How can my pet be treated?

The mainstays of treatment involve decreasing the inflammation associated with the disease and medication to eradicate the E cuniculi. With proper treatment, some animals will recover completely, others may always show some clinical signs, and unfortunately in the case of advanced disease the rabbit may die.

Rabbits that partially recover may need to remain on medications for life to help control the disease. Those rabbits with the renal form of the disease may require renal support especially during the acute phase of the disease or possibly for life. The cataracts associated with the ocular form may eventually rupture resulting in uveitis. If this occurs, sometimes the eye must be removed for the pet’s comfort.

While E. cuniculi is not the only cause for neurologic disease in a rabbit, it is important to keep this in mind if your rabbit ever exhibits any of the above mentioned clinical signs. 

Dr. Jennifer Ivankovig has been a part of the Animal House of Chicago team for nearly 10 years. She has a special interest in rabbits and other exotic pets.