A possum around the barn could be detrimental to a horse's health because possums are carriers of equine protozoal myeloencephalitis (EPM), a neurological disease they acquire from eating dead birds. The disease itself is caused by a single-celled protozoa by the name of Sarcocystis neurona.
As part of its life cycle, this parasite may travel through a opossum and infects the cells in the animal's gut. It is then passed out of the possum in its feces, which, in turn, can be ingested by horses grazing in the pasture or in hay kept in a loft.
The bad news is that more than 50 percent of all horses are exposed to the parasite.
The good news is that only a few actually become affected by disease, which may require an immunity deficiency in the horse for the disease to actually become fatal.
EPM is hard to diagnose because it mimics other diseases, such as Wobbler's syndrome, equine herpes and West Nile virus.
The disease effects the horse by inflaming tissue around the parasite within the spinal cord.
Eliminating possums around a barn or horse pasture reduces the chances of horses contracting EPM.
The disease is not transmitted between infected horses -- only between possums (and possum scat) and horses.
Bottom line: If your farmer has horses, offer to toss the terriers up into the hayloft a couple if times in the Fall and Winter when possums are most likley to be looking for winter shelter. A warning, however: Be able and ready to move those large round bales should your dog find deep in the stack.