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EPM has is generally described as debilitating, but not painful to the horse, but for the owner it can be elusive, confusing, costly, and the cause of great frustration. The disease is caused by one of two protozoa, Sarcocystis neurona or Neospora hughesi; both infections are treated with the same drug protocols. The life cycle of S. neurona is dependant upon the opossum. This makes the disease naturally occurring only where the opossum lives (for more information about opossums click here). A horse becomes infected by ingesting the protozoa in feed, hay, pasture or water contaminated with opossum feces. The opossum is the definitive host for the protozoa S. neurona, which causes most cases of EPM. The opossum is infected by feeding on a carcass of an infected intermediate host such as the raccoon, armadillo, skunk, birds, or domestic cat. Once the opossum consumes the immature stage of the protozoa from a carcass, it takes about two to four weeks for the protozoa to mature and be shed in the opossum feces.

The protozoa must cycle between the opossum and an intermediate host to complete its life cycle. Most researchers consider the horse to be an aberrant host – one that can become infected, but not act as the intermediate host to complete the life cycle. Infected horses do not shed the protozoa in manure, so HORSES CANNOT INFECT OTHER HORSES.

Opossums are primarily nocturnal and live in a variety of habitats. Opossums are highly adaptable and can be found not only in wooded areas and along streams, but also in developed areas including neighborhoods and in and around farm buildings. An omnivore, the opossum will eat a variety of items including carrion, berries, cat food, sweet feed, and human snacks left in the trash. It has a very good sense of smell. They need a source of water, and are drawn to the riparian buffers along streams or human made water sources such as livestock watering systems, pools, ponds and even lawn irrigation systems. Opossums are a necessary part of the ecosystem, cleaning up carrion, and proving food for animals higher in the food chain; however they can quickly become a nuisance when they decide to take up residence in buildings and feed on pet or livestock feed and trash. You can learn more about opossums by clicking here.

Horses are infected by ingesting feed or water that has been contaminated with opossum feces. It is important to keep hay and grain in secure locations where wildlife cannot come into contact with it. Feed tubs located on the ground are easier for opossums to enter, increasing the risk of contamination. Opossums defecating in open water sources including streams can produce another source of infection. Horses may ingest S. neurona in pastures located near wooded areas or fence rows with thick brush where opossums travel and look for food.

Keeping opossums out of the barn can be a challenge and will require diligence. They are good climbers and may enter the barn through stall doors, windows and even vents. Our technicians can help you identify problem areas. Opossums are also scavangers always looking for an easy meal. Be sure to pick up cat food every night, and store it in a raccoon/opossum proof container. Sweep up spilled grain, and empty the trash can often. Keeping food items locked up or out of the barn will make it less tempting for opossums to enter.

Depending on the location and population, trapping and removing the opossums from the area may be a good solution. This involves either euthanizing or relocating the trapped animal. Euthanizing the opossum is not fun, and may not be legal in your location. Relocating the trapped animal may give you peace of mind, but you have transported the animal outside of its territory, and it may not survive long in a new location. If you transport it to an area near other farms, you may create headaches for other equine owners. Our technicians can help you determine the best solutions for exclusion and removal of opossums in and around our horses. Contact us today for an inspection.

For more information about EPM and your horse here is a resource:

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