Study: EPM's Causative Agents More Widespread than Expected

Study: EPM's Causative Agents More Widespread than Expected

Geographic Distribution of Horses with Antibodies Against EPM-causing Parasites

Photo: University of California, Davis, School of Veterinary Medicine

A recent study by researchers at the University of California, Davis (UC Davis), School of Veterinary Medicine confirmed that equine protozoal myeloencephalitis (EPM), caused by two different parasites, is widespread throughout the United States. The single-celled protozoal parasite Sarcocystis neurona, which is shed in the feces of opossums, is the most commonly recognized cause of this neurologic disease in horses. However, this study found evidence that Neospora hughesi, the other EPM-causing agent first identified in California, is now being identified in horses across the United States.

After obtaining a total of 3,123 diagnostic submissions from 49 states, UC Davis researchers determined that horses from 42 states were affected by parasites causing EPM (see map above left). Horses in 24 states tested positive for antibodies against both N. hughesi and S. neurona. Horses from 17 states tested positive for antibodies against S. neurona only, while horses in one state—Idaho—tested positive for antibodies against N. hughesi only. As these results show a widespread distribution of the parasites causing EPM, horse owners and practitioners should test EPM-suspect horses for antibodies against both parasites.

“This study returned positive results from more states than we originally thought,” said Nicola Pusterla, DVM, PhD, Dipl. ACVIM, associate professor of equine internal medicine at UC Davis and lead researcher on the study. “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. Overall, we had not been satisfied with the standard testing available, so we have spent the past decade developing and successfully validating an improved diagnostic tool for EPM.”

The new SarcoFluor and NeoFluor tests created by UC Davis are immunofluorescent antibody tests for both of the known causative agents of EPM. These tests provide a quantitative indication of EPM infection and, and the researchers say the tests provide greater sensitivity and specificity than the Western immunoblot test on serum samples. UC Davis’ tests also reduce the necessity to obtain cerebrospinal fluid in order to screen for antibodies against the two protozoal agents, the researchers say.

Horses affected by either of the parasites that causes EPM often appear neurologic.

Photo Courtesy UC Davis

“UC Davis has a rich history and culture of combining rigorous peer-reviewed research with cutting edge medicine,” said Patricia Conrad, DVM, PhD, professor and head of the laboratory at UC Davis that developed the tests. “The resources and EPM team of clinicians and scientists available at UC Davis have allowed us to validate these more effective tests. We are committed to improving the reliability of EPM testing, and are pleased to offer this service to our clients at a reasonable cost.”

“Since its discovery in horses, EPM has posed a significant diagnostic and therapeutic challenge,” said Claudia Sonder, DVM, director of the Center for Equine Health at UC Davis. “These new diagnostic tools are a product of the team science that changes clinical outcomes for horses treated at UC Davis.”

The new tests are available through the laboratory services at the UC Davis Veterinary Medical Teaching Hospital (VMTH). To learn how to submit samples, contact VMTH laboratory services at 530/752-VMTH or visit the UC Davis website.

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