Reduce EPM Exposure

You know opossums can pass equine protozoal myeloencephalitis (EPM) to your horse (see the May 2004 issue of Horse & Rider, “A Lucky Stumble”) But there are other animals that act as intermediary hosts and carry Sarcocystis neurona–the parasite that causes EPM by invading a horse’s spinal cord. Here’s more information on the parasite’s life cycle–and some tips for reducing your horse’s risk.

Sarcocystis neurona is passed to horses through feed contaminated by opposum feces. Cover hay with a tarp until feeding time. | ? Darrell Dodds

Enemy #1
Opossums are the critical link in EPM’s transmission by passing sporocysts (the stage of the parasite that infects horses) in their feces. Your horse can pick up sporocysts in feces-contaminated feed or water. But how do opossums get the parasite to begin with? They eat the infected muscle tissue of an intermediate host species–animals that carry the parasite at different stages in its life cycle.

Intermediate Hosts
Researchers have identified the nine-banded armadillo as an intermediate host, along with striped skunks and raccoons. Also on the suspect list are the brown-headed cowbird and the domestic house cat.

Reducing the Risk
So what can you do to control the spread of the parasite and reduce the risk of your horses getting the disease?

  • Keep feed storage areas as clean as possible: Put grain in tight containers and keep hay storage areas clean. Cover hay with a tarp if you have birds in the rafters, and remove or tightly cover any food or garbage (including food for cats and dogs).
  • Keep opossums away from the area where horses, water and feed storage are located–since opossums will climb, but won’t dig, try using wire mesh fencing with a hot wire strung around the outside.
  • If you have opossums, you may be able to trap and relocate them. You can usually purchase a humane trap for about $40. Use peanut butter, fruit or cookies as a lure. (Don’t use meat or cat food, as you may end up trapping a cat instead.) Be sure to check with wildlife or animal control officers for wildlife laws and regulations governing trapping and relocating opossums.
  • Consider allowing hunters and trappers permission to take opossums on your property during legal hunting seasons (check with the wildlife or fish and game department).

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