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EPM more widespread than expected among US horses – study

Geographic distribution of horses with antibodies against EPM-causing parasites. Image: UC Davis

Geographic distribution of horses with antibodies against EPM-causing parasites. Image: UC Davis

A recent study by American researchers reveals 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 neurological disease in horses.

However, this study by researchers at the University of California, Davis School of Veterinary Medicine found evidence that Neospora hughesi, the other EPM-causing parasite, first identified in California, is now being identified in horses across the United States.

After obtaining a total of 3123 diagnostic submissions from 49 states, UC Davis determined that horses from 42 states were affected by parasites causing EPM.

Horses in 24 states tested positive for antibodies against Neospora hughesi and Sarcocystis neurona. Horses from 17 states tested positive for antibodies against Sarcocystis neurona only, while horses in one state tested positive for antibodies against Neospora hughesi only.

The researchers said that, because these results showed a widespread distribution of the parasites causing EPM, horse owners and practitioners should test horses suspected of having EPM for antibodies against both parasites.

“This study returned positive results from more states than we originally thought,” said D. Nicola Pusterla, lead researcher on the study.

Horses affected by the parasites that cause EPM may show neurological signs. Photo: UC Davis.

Horses affected by the parasites that cause EPM may show neurological signs. Photo: UC Davis.

“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 SarcoFluor and NeoFluor tests created by UC Davis are immunofluorescent antibody tests for both of the known causative agents of EPM (Sarcocystis neurona and Neospora hughesi).

These tests provide a quantitative indication of EPM infection and provide greater sensitivity and specificity than the Western immunoblot test on serum samples, the researchers say.

UC Davis’ tests also reduce the necessity to obtain cerebrospinal fluid in order to screen for antibodies against the two protozoal agents.

Dr Patricia Conrad, professor and head of the laboratory at UC Davis that developed the tests, said clinicians and scientists had used the resources available at UC Davis to validate the new tests.

Dr Claudia Sonder, director of the Center for Equine Health at UC Davis, said: “Since its discovery in horses, EPM has posed a significant diagnostic and therapeutic challenge.

For the first time, she said, veterinarians can associate probability of EPM infection with positive tests results, and can rule out both organisms known to cause EPM with negative tests.

“This advancement in diagnostic capability is much welcomed by all faced with this complicated disease.”

The tests are available through the laboratory services at the UC Davis Veterinary Medical Teaching Hospital. For more information, contact VMTH laboratory services at 530-752-VMTH or go online here.

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