Equine protozoal myeloencephalitiscan can spread to horses who eat hay, feed or drink water that is contaminated with opossum feces. EPM is a rare disease. Studies suggest that about one third of opossums are infected in Missouri compared to one tenth of opossums infected in Michigan.
Not every horse that eats contaminated feed develops EPM and not every opossum is infected with the parasite. Still it is best to not feed horses any hay or feed that is contaminated with opossum feces and to opossum proof areas where feed and hay are kept.
Source: The Paulick Report, University of Minnesota Extension, March 3, 2023. Link.
INSIGHTS: The author references opossums as tick eaters. However a study we shared in February 2022 refutes that claim saying opossums DO NOT like eating ticks <Link>.