Encephalitozoon cuniculi (E. cuniculi)

By Jenna Richardson BVM&S MRCVS,
Rabbit, Exotic Animal and Wildlife Clinician at Royal (Dick) School of Veterinary Studies

What is Encephalitozoon cuniculi (E. cuniculi)?

E. cuniculi is a protozoan parasite that causes the disease encephalitozoonosis. It primarily affects the nervous system (brain and spinal cord) and kidneys. E. cuniculi spores are spread in urine from an infected rabbit and are then eaten (or less commonly, inhaled) to infect another rabbit. The parasite can also be transmitted from mother to young during pregnancy. Other animals can be carriers of the parasite including wild rabbits and rodents, however most will be asymptomatic and few are found to be affected by disease.

Can humans develop E. cuniculi?

Yes, humans can develop the disease, as the parasite is zoonotic. Generally only severely immunocompromised individuals are at risk.

What signs will a rabbit show with E. cuniculi?

If a pregnant doe is infected, the E. cuniculi parasite can infect the eyes of the unborn kits. This may cause destruction of the lens and eye later in life (usually from 6 months to 2 years old). The rabbit may develop a cataract and the eye may become red and swollen.

The most common presenting sign, in mature rabbits, is hind leg weakness and, in advanced cases, paralysis. This is thought to result from the swelling surrounding the parasite in the spinal column, causing destruction of the nervous tissue. Other clinical signs seen include:

• Head tilt
• Fitting
• Loss of balance
• Tremors
• Bladder weakness
• Kidney failure

Once the rabbit develops severe clinical signs, euthanasia should be advised. If left untreated death can result.

Signs of kidney failure, as with other species, may include increased thirst, increased urination, weight loss and decreased appetite.

How can you test a rabbit for E. cuniculi? Blood tests:

A blood test can be performed to measure antibodies, however the helpfulness of this is limited as it only tells us that the rabbit has been exposed to E. cuniculi at some stage in its life. In a recent study, over 50% of healthy rabbits were found to have E. cuniculi antibodies, which makes interpretation of blood results difficult. So if the rabbit is showing signs of disease that are suggestive of encephalitozoonosis, a positive test does not necessarily mean that the parasite is causing these signs.

More information indicating the stage of infection and immune response can be obtained by taking two blood samples one month apart. Rising antibody levels between the two blood samples is suggestive of a current, active infection or flare up. Unfortunately, if the antibody levels are the same at the first and second blood sample, then no true conclusion can be reached.

If the antibody levels to E. cuniculi are falling between samples, then this is suggestive that the rabbit is recovering from a recent infection. This would imply that a treatment regime is having a positive effect.

The two types of antibodies that should be tested for are IgM and IgG. Testing for both could provide a better indication of the infective status of the affected rabbit.

IgM is more indicative of a current active infection.

IgG indicates long-term exposure, with levels continuing to rise steadily from 30 days post infection until they peak at 70 days post infection. If the rabbit tests negative for IgG, then E. cuniculi can definitely be ruled out.

If titres are very high positive and typical clinical signs are present, then the test is more likely to be diagnostic.

A general blood screen including urea and creatinine levels would be useful for both general health assessment and kidney health evaluation.

How can you test a rabbit for E. cuniculi? Urine tests:

There is now a simple urine test that can confirm if the rabbit is actively shedding the parasite. Usually the parasite is shed in the first 3 months after the rabbit is infected, although it can still be shed intermittently after that. Urine samples should be collected over a 3 day period and sent to the laboratory.

N.B. A negative result is not conclusive, as the rabbit may not have been shedding the parasite during the urine collection time.

A urine protein creatine ratio cannot be used as a diagnostic test.

How can you test a rabbit for E. cuniculi? Tissue biopsy:

This is the most accurate way of confirming a rabbit has the disease. Under general anaesthetic a small biopsy of kidney tissue is obtained. Laparoscopy is the least invasive method of obtaining a sample. It is not possible to biopsy central nervous tissue.

What treatment is available for this condition?

When clinical signs are advanced, only supportive care can be implemented as there is currently no treatment that will reverse the damage already caused by the parasite. Symptomatic treatment can be provided to support the signs of bladder or nervous system disorders.

Fenbendazole (Lapizole®) can slow or halt the rate of multiplication of the E. cuniculi parasite within the body. Daily dosing is required for a minimum period of 28 days – 1 ml/kg/day by mouth.

How can I prevent a rabbit getting E. cuniculi?

All rabbits recently acquired, regardless of background, should receive a single course of Lapizole for 4 weeks by mouth. This treatment is based on the theory that if the rabbit is carrying E. cuniculi, Lapizole will kill the parasite before it causes further damage. This in turn may prevent clinical signs from developing.

It should be noted that treating a rabbit with Lapizole that does not have E. cuniculi should not cause any adverse effects.

There is no lasting effect of Lapizole, therefore if a rabbit comes into contact with the protozoan after receiving the treatment course, it is still at risk of developing the disease.

Any new rabbits entering a home with other rabbits should undergo a quarantine and treatment period.

If putting a rabbit in a pre-existing hutch or run, then hygiene is crucial. Spores are relatively resistant to environmental change. At average temperatures, and in dry conditions, the average spore survival time is four weeks. The parasite is, however, easily killed with contact with bleach 1-10% for a minimum of 30 seconds.