When it comes to equine protozoal myeloencephalitis (EPM), the sooner a veterinarian reaches a diagnosis and treatment can begin, the better the horse’s chances are for recovery.

This serious neurologic disease of horses primarily caused by Sarcocystis neurona, a protozoan parasite that invades the brain, brainstem, and spinal cord. Another protozoan parasite, Neospora hughesi, is a less common cause of EPM.

One study indicates that, overall, 78% of U.S. horses have antibodies against S. neurona and 34% have antibodies against N. hughesi. However, less than 1% exposed to EPM will develop clinical signs.

S. neurona is spread to horses from a definitive host, in this case, an opossum. Horses become infected with EPM through contact with opossum feces through grazing or contaminated feed. The definitive life cycle of N. hughesi is not yet fully understood.

In a horse’s life, there can be a time when he is considered seropositive, meaning the horse has been exposed to the EPM’s causative parasites. Some horses harbor the parasite for months or years and then slowly or suddenly develop signs, while others might never develop signs of EPM.

Because horses have such a high chance of being exposed to S. neurona and/or N. hughesi, horse owners should be aware of EPM’s subtle early clinical signs so they can promptly consult their veterinarian for diagnosis and treatment.

Update: EPM in Horses

SPECIAL FEATURE: Update: EPM in Horses

Some of the signs horse owners should watch for include:

While virtually every horse is at risk, some horses are at greater risk than others, with age, time of year, location, training and history all potentially affecting a horse’s susceptibility. For those horses that are exposed to S. neurona or N. hughesi, stress from things such as travel or training can compromise the immune system, thus potentially activating the disease.

“Early detection by horse owners and farm managers, diagnosis by a veterinarian and an effective treatment plan are the keys to stopping the progression of the disease,” says Sarah Reuss, VMD, Dipl. ACVIM, an equine professional services veterinarian for Boehringer Ingelheim. “The faster treatment begins, the better the chance for the horse to recover.”

Your horse might have been exposed to EPM’s causative parasites EPM. Make sure you’re aware of the subtle signs of this debilitating neurologic disease so you can promptly contact your veterinarian.