Mar 15, 2018

Sarcocystis – A new neurological disease in rabbits?



In the last few years at House Rabbit Society headquarters in Richmond, CA, we have seen a number of rabbits with neurological symptoms that are different than what we would expect with E. cuniculi. From 2016-2018, we have found 34 rabbits with neurological symptoms who have tested positive for a parasite called Sarcocystis, using a PCR blood test. Two rabbits with neurological symptoms passed away and on necropsy were found to have Sarcocystis in their brain tissue or spinal fluid, using a PCR test, and unidentified organisms were seen in brain tissue upon histopathology. Most of these rabbits have tested negative for E. cuniculi.

These rabbits have come from at least 6 counties in Northern California (Alameda, Contra Costa, San Francisco, San Mateo, Santa Clara, and Sacramento), Ventura County in Southern California, Chicago, IL, Pittsburgh, PA, and Huntington, NY.

House Rabbit Society is not currently enrolling additional rabbits with neurological symptoms in the study.

What is Sarcocystis?

Sarcocystis is a genus of single-celled parasites that have a two-host lifecycle. The definitive host is generally a wildlife predator species, and a prey animal contracts the parasite by eating feces-contaminated grass or plants. The infected prey animal must be eaten by a predator to transmit the parasite, and the predator’s feces can then contaminate plants.

There are many different species of Sarcocystsis that affect different animals. S. neurona causes neurological symptoms in horses and sea mammals, while S. falcatula causes neurological symptoms in birds of prey. House Rabbit Society is doing DNA sequencing to try to determine which species of Sarcocystis is being found in rabbits. At this point, we know the species affecting rabbits is not S. neurona or S. falcatula, but there are many species of Sarcocystis, and it’s possible this could even be a closely related Apicomplexa.

What are the symptoms of rabbits with neurological symptoms who have tested positive for Sarcocystis?

The most common symptom of rabbits who have tested positive for Sarcocystis is ataxia. The rabbits have a “drunken” appearance and are wobbly when they hop, often have intention tremors where the wobbling is worse when they’re trying to move towards something, and might fall over. They might also have weakness in a hind-limb, and the weakness, ataxia, and falling over may get progressively worse. Other symptoms have included: seizures, turning in circles, head tilt, rolling, and stargazing.

Here are videos of rabbits who are positive for Sarcocystis.

House Rabbit Society has tested some healthy rabbits who tested positive for Sarcocystis, but those rabbits have not developed neurological symptoms. At this point, it appears that not all rabbits who have been exposed to the parasite will develop neurological symptoms.

How can I prevent my rabbit from getting Sarcocystis?

Rabbits cannot catch Sarcocystis from each other. Housing your rabbit indoors will prevent your rabbit from coming into contact with wildlife or predator feces. If you live in an area where you see wildlife like opossums or skunks, or in an area where there have been other rabbits diagnosed with Sarcocystis, you may want to restrict outdoor playtime for your rabbit or put down a clean blanket/rug outside covering the exercise area before providing supervised outdoor playtime.

Is there treatment for Sarcocystis?

House Rabbit Society has been treating rabbits who have tested positive with Ponazuril and/or ReBalance. Both of these drugs were developed to treat S. neurona in horses. While these drugs seem to help stabilize some of the affected rabbits, others have had progressively worsening neurological symptoms or have died. As we learn more about Sarcocystis in rabbits, we hope to be able to help find new treatments.

If you are a veterinarian and would like to learn more, you are welcome to email us.

