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E-Cuniculi in Rabbits

What is E-Cuniculi? (Encephalitozoon cuniculi)

It is a tiny protozoan parasite that lives inside of a bunny's body that can cause a number of major health problems. Once infected, it is carried, via blood, through organs (liver, kidney, central nervous system -- brain and spinal cord), the parasites have the possibility to rupture the organ cells; causing inflammation and clinical signs. Research estimates that, in the US, over 60% of healthy rabbits were found with e-cuniculi antibodies, but a small percentage - approximately 6% - of pet bunnies ever show symptoms.

How is E-Cuniculi Transmitted?

It is passed through spores within the urine, which can then be picked up by other bunnies who ingest these spores; e.g: urine contaminated food/water. Many bunnies are born with the parasites, as kits are infected during birth if the mother is a host.

These parasites are able to replicate within the kidneys to be shed in the urine. It is only while e-cuniculi is in the kidneys that the infected bunny is contagious. According to a 2013 study the duration of spore excretion is 17-31 days consistently, then sporadically for 90 days in bunnies over 6 months of age, for those between 12-21 weeks it is consistently for up to 63 days.

Symptoms of E-Cuniculi?

Can include but not limited to:

  • Neurological Disease (Head tilt, unsteadiness, urinary incontinence)

  • Kidney Disease

  • Eye Disease (Cataracts)

-- Note that other causes should be explored before assuming e-cuniculi. --

Many times the parasites can be found throughout the body, but remain dormant without causing damage. If they replicate, that is when damage can occur.

Research shows that symptoms usually appear if the bunny is compromised by other types of infections or stress, as the immune system splits focus to both illnesses, which may cause a "unexpected" symptom to appear. (e.g: My bunny got snuffles and lost the use of his hind legs.)

How do you diagnosis E-Cuniculi?

A vet can order a blood test done which looks for antibodies to e-cuniculi. This confirms exposure, but does not confirm that the bunny will show symptoms. This test is expensive, approximately $125 for the panel of IgG, IgM, and CRP.

"Testing is complicated and results have to be interpreted in light of clinical signs.  Dr. Cray of Miami study: Ruling out the disease is easier than ruling in. Clinically suspect rabbits in her study tended to have higher titers for IgG and IgM. With Dr. Cray's research if a rabbit patient had a positive antibody titer combination on serological testing of IgG > 512 and IgM > 64, the positive predictive value is high (92%). According to Dr. Cray, a negative result for IgM and IgG could represent a presumptive negative test for that patient. Thus, while positive titers are understandably difficult to interpret, a negative titer may be helpful in ruling out ECUN as a causal agent of illness." (Dr. Vetter, East Towne Pet Clinic)

Is E-Cuniculi Treatable?

Treatment is oftentimes the anti-parasiticide Paracur or Lapizole (fenbendazole) which is taken daily for 28 days. "There is very little evidence that it can treat an existing infection. It has been shown to help prevent infection when given to rabbits at high risk and may help reduce spore formation and reinfection. Supportive care - fluids, control of dizziness, appetite support are more important while giving a rabbit time to recover from acute infection." (Dr. Vetter, East Towne Pet Clinic) The cost of fenbendazole is approximately $20, however cost of supportive care exceeds this: syringe feeding, fluids, anti-nausea medications, etc. Treatment with these medications are high risk. Evidence suggests that during treatment for the full 28 days may cause bone marrow depression. 


The parasite can live outside of the host for one month. With the treatment, the parasite is killed within the host. However, treatment does not prevent reinfection. So if the environment still has the parasite, or consumes the spores from an infected host, they are likely to reintroduce the parasites.

Another item to keep in mind that if the bunny experiences symptoms prior to treatment, it does not ensure the symptoms will go away. When it concerns neurological damage, what has been done if often times permanent


E-cuniculi is not a death sentence. Although contagious, even for a temporary time, according to a study performed by the House Rabbit Society, they found that 12% of rabbits with high titers (concentration) develop neurological disorders. Very few deaths have been directly attributable to e-cuniculi. The majority of bunnies are able to live a long, happy life even being infected with e-cuniculi.


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