Two protozoal parasites causing widespread equine disease, study finds


UC-Davis says Neospora hughesi, first identified in California, causing EPM in horses across the country along with Sarcocystis neurona.

Photo courtesy of UC-Davis

Researchers at the University of California-Davis School of Veterinary Medicine say the neurological disease equine protozoal myeloencephalitis (EPM) is widespread across the United States. A single-cell protozoal parasite, Sarcocystis neurona, shed in the feces of opossums is the most commonly recognized cause of EPM. However, a recent UC-Davis study found evidence that Neospora hughesi, the other EPM-causing parasite, first identified in California, is now being identified in horses across the United States.

“This study returned positive results from more states than we originally thought,” says UC-Davis’s Nicola Pusterla, DVM, DACVIM, lead researcher on the study, in a university release. “As the recognized geographic spread of Neospora hughesi infections expands, we are encouraging horse owners about the benefits of the advanced tests available at UC-Davis to more accurately diagnose the disease.”According to the university, researchers obtained a total of 3,123 diagnostic submissions from 49 states for the study. They determined that horses from 42 states were affected by parasites causing EPM. Horses in 24 states tested positive for antibodies against N. hughesi and S. neurona. Horses from 17 states tested positive for antibodies against S. neurona only, while horses in one state tested positive for antibodies against N. hughesi only.

The immunofluorescent antibody tests SarcoFluor and NeoFluor created by UC-Davis are designed to identify both of the known causative agents of EPM. The university says the tests provide a quantitative indication of EPM infection and provide greater sensitivity and specificity than the Western immunoblot test on serum samples while reducing the necessity to obtain cerebrospinal fluid in order to screen for antibodies against the two protozoal agents.

“Since its discovery in horses, EPM has posed a significant diagnostic and therapeutic challenge,” says Claudia Sonder, DVM, director of the Center for Equine Health at UC-Davis. “For the first time, veterinarians can associate probability of EPM infection with positive tests results and can rule out both organisms known to cause EPM with negative tests.”

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