![]() ![]() Trapping data provided by the Ontario Ministry of Natural Resources (OMNR) for 1998, indicates that opossums were present in the districts of Niagara, Cambridge, Simcoe, Aylmer, Chatham, Wingham, Maple, Owen Sound and Midhurst. Horses staying for short terms in endemic areas may become infected and show disease symptoms later, while resident in non-endemic areas. EPM will be found most commonly in horses that reside in areas inhabited by opossums. neurona since it cannot transmit the disease to other horses. The horse is considered a dead-end host for S. Once the sporocysts have been ingested, they migrate from the intestinal tract into the blood stream, cross the blood/brain barrier and attack the central nervous system. Horses are infected incidentally when they eat feed contaminated with the feces of opossum, which contain infective sporocysts. The large number of road-killed animals in some areas may contribute to the spread of the disease. The opossum is a nocturnal animal, a scavenger by nature and eats anything, including carrion. Currently, the armadillo, domestic cat, skunk and raccoon have been identified as intermediary hosts pertinent to the life cycle of the disease (3). The life cycle is complete when opossums eat infected dead intermediary hosts. Intermediate hosts ingest the sporocysts where they, in turn, develop into sarcocysts in muscle tissue (3). The opossum excretes oocysts in the stool, which develop into infective sporocysts in the environment. In this disease, the life cycle involves the final or definitive host, the opossum ( Didelphis virginiana). Generally Sarcocystis species have a life cycle that involves predator and prey animals. These organisms have a predilection for the central nervous system in horses. Closely related parasites, Neospora spp., and particularly Neospora hughesi, have been isolated as the cause in a few cases (1,2). Although identified as a protozoal disease in 1974, the specific disease-causing agent, S. The primary parasite that causes the disease is the single-celled protozoal organism Sarcocystis neurona. Refer to the information sheet, Equine Viral Encephalitis for further information. EPM can look like other equine neurologic diseases, including Wobbler syndrome, the neurological form of herpes virus infection (nEHV-1), rabies, West Nile virus or other equine viral encephalitis diseases, e.g., Eastern and Western equine encephalitis. The signs in individual horses range in severity and may include incoordination, weakness, spasticity and muscle loss. This disease can be difficult for owners and veterinarians to diagnose and treat. In some areas of North America, Equine Protozoal Myeloencephalitis (EPM) is one of the most important neurologic diseases in horses. ![]()
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