Researchers at the USDA and The Ohio State University (OSU) have found that the raccoon can serve as an intermediate host for Sarcocystis neurona, the single-celled protozoan parasite that causes the neurological disease equine protozoal myeloencephalitis (EPM). The study was published in a recent issue of Veterinary Parasitology. Another paper published in the same journal suggests that S. neurona exposure rates (indicated by serological or blood serum test findings) are similar in raccoons and horses.

The research group completed the S. neurona life cycle earlier this year for the first time in the laboratory with the domestic cat, and had been working on the current study since June. Two other intermediate hosts have been pinpointed in the spread of S. neurona–the nine-banded armadillo and the striped skunk–but the only other proven natural intermediate host is the armadillo, which lives in the southern region of the United States. The wide geographic range of the raccoon might explain why we see EPM in so many parts of the United States.

According to William Saville, DVM, PhD, Dipl. ACVIM, a principal investigator in the study, the researchers chose the raccoon as a potential intermediate host because it is a scavenger and because its potential role in EPM had not been examined closely before.

Saville and his colleagues took muscle from raccoons that were picked up through a pest control company and fed it to naïve opossums, which in turn shed S. neurona sporocysts in their feces. The sporocysts were fed to “knockout mice” (genetically altered, immunocompromised mice used for studying EPM), which then developed neurologic disease