Skunk Revealed as an EPM Intermediate Host

Researchers have discovered that the striped skunk can serve as an intermediate host in the laboratory for Sarcocystis neurona, the single-celled protozoan parasite that causes equine protozoal myeloencephalitis (EPM). The striped skunk's range of habitat encompasses much of the United States, Canada, and northern Mexico, so this discovery better explains the wide geographic distribution of EPM in horses.

This study was a collaboration of researchers from the University of Florida (UF), Washington State University, and the University of Missouri. Ellis Greiner, PhD, a professor in the department of pathobiology at Florida's College of Veterinary Medicine, said, "Major research contributions are made by teams in this day and age; I don't think any of us could do this alone."

Striped skunks initially negative for antibodies to S. neurona were inoculated with the parasite collected from a naturally infected opossum. Skunks developed antibodies to S. neurona, sarcocysts developed in their muscles, and the muscles were fed to laboratory-reared opossums that then shed the S. neurona sporocysts in their feces. A pony foal and laboratory mice were then inoculated with sporocysts. The foal developed antibodies to S. neurona in his cerebrospinal fluid. The mice developed antibodies and central nervous system disease, and died or were euthanized.

"The beauty of it is that this fills out the rest of S. neurona's range for North America and explains how opossums could be infected where we don't have armadillos," explained Greiner. The domestic cat also has been identified as an intermediate host in the laboratory, although it hasn't been proven as a natural intermediate host.

"The skunk has been reported to be naturally infected with sarcocysts, therefore it is highly likely to be a natural intermediate host," said Cheadle. "Reports of naturally infected skunks are needed to provide definitive data implicating them as an intermediate host in nature."

Several research groups are investigating other possible hosts. "I have an inkling that raccoons might be intermediate hosts, too, based on similar data," said Cheadle. Raccoons can have a Sarcocystis species in their muscles that is very similar in structure to those in skunks.

The research group next will try to confirm that the cycle involving the skunk can be completed in nature.

"We have a very limited skunk population in Florida, so we're going to collaborate with another university (in an area with a larger skunk population). They're going to collect skunks and we will do the tissue work, as well as confirm the identity of the parasite," he explained.

In the meantime, elimination of skunks isn't the answer to keeping EPM out of your horses.

"A hundred skunks in a pasture won't do a thing to a horse--the opossum is (still) the obvious source of infection," said Greiner.

About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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