Opossums and Equine Protozoal Myeloencephalitis

Equine protozoal myeloencephalitis, also known as EPM, is a dreaded fear for many horse owners— and understandably so. This condition is very serious and can be difficult and expensive to treat.

Opossums are short-term hosts for the parasite that causes EPM, and horses contract it when an opossum poops in its feed. A lot of horse owners interpret this to mean that the best way to protect their horses is to kill or remove opossums from their property.

Science has shown that this doesn’t work, for a few reasons. Opossums are master scavengers and will move into any suitable territory, so moving or killing a handful of opossums will just invite others to move in. In the absence of opossums, rodents and raccoons lose their main competitors and will take over the open territory, and are more likely to carry diseases than opossums. Opossums also eat thousands of ticks every week, so moving them away from your property will inevitably lead to an explosion of ticks, as well as the serious diseases they carry.

So what’s a concerned horse owner to do? The first step is to make sure you’re storing your feed in sanitary conditions to whatever extent you’re able. The second is to dispose of animal carcasses as soon as possible when you find them on your property. Believe it or not, opossums don’t naturally carry the EPM parasite, but actually ingest it when eating decaying cats, skunks, and raccoons, which are key hosts for one phase of the parasite’s life cycle.

If you have barn cats, keep their populations in check through spaying and neutering, and make sure they are vaccinated and in good health, to minimize the chances of an opossum finding and eating deceased cats.

Any case of EPM is a tragedy, and no horse or its owner should have to endure such a disaster. But mass-exterminating opossums can’t solve the problem. We need to learn steps to safely coexist.