EPM: Don’t Blame the Barn Cats

Equine protozoal myeloencephalitis, or EPM, is caused by Sarcocystis neurona protozoa. Carried by opossums and shed in their feces, S. neurona is frequently spread to raccoons and skunks when these animals consume opossum droppings. According to a note in Equus, antibodies against S. neurona have been found in barn cats but at a much lower rate (only 7%) than raccoons (100%) and skunks (46%). All three can become intermediate hosts if their tissues are eaten by an opossum, infecting the opossum and allowing it to transmit oocysts to the environment and to horses through contamination of grass, hay, or feed with fecal material. The numbers show that cats are less likely than skunks and raccoons to be exposed to the organism and act as intermediate hosts. Intermediate hosts play a part in the life cycle of S. neurona, but unlike opossums, these animals can’t actually spread EPM to horses.