EPM organisms are hard to avoid

New study confirms that many American horses are exposed to the organisms that cause equine protozoal myeloencephalitis (EPM).
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A new study underscores the prevalence of exposure to the organisms that cause equine protozoal myeloencephalitis (EPM) among American horses.

A opossum walking through a field of grass and leaves.

The organisms that cause EPM are passed to horses through the feces of infected opossums.

A progressive neurologic disease characterized by inflammation of the brain and the spinal cord, EPM is caused by two types of protozoans, Sarcocystis neurona and—less often—Neospora hughesi. The organisms are passed to horses through feed contaminated with feces from infected opossums. Most horses who ingest the protozoans do not show signs of disease, but in some cases the organisms cross the blood-brain barrier and attack the central nervous system, leading to the weakness, incoordination and muscle atrophy characteristic of EPM.

For the study, which was conducted in the fall of 2013, University of California–Davis researchers collected blood samples from 5,250 healthy horses in 18 states and tested them for antibodies to both S. neurona and N. hughesi. They found that 78 percent of the horses were seropositive for S. neurona, and 34 percent were seropositive for N. hughesi. Thirty-one percent of the horses were seropositive for both organisms and 18 percent did not carry antibodies to either organism.

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The data also showed that warmbloods and horses younger than 5 were more likely to carry antibodies to both protozoans than were other horses.

In addition, horses in the South were more likely to be exposed to S. neurona, but exposure to N. hughesi did not vary among geo-graphic regions.

Reference: “Seroprevalences of anti-Sarcocystis neurona and anti-Neospora hughesi antibodies among healthy equids in the United States,” Journal of the American Veterinary Medical Association, June 2017

This article was originally published in EQUUS 485, February 2018

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