TRAVERSE CITY — About a month ago, Nancy Reye was horseback riding and noticed the rear of her horse seemed weak.
I couldn’t get her going; she felt weak underneath me,” she said. “I thought it was a hoof, a joint, but nothing was showing up. Then I rode her one night and she could hardly balance me. It was almost kind of scary.”
Reye guessed her horse, Ellie, was suffering from equine protozoal myeloencephalitis, or EPM, a serious and often fatal neurological disease. That’s because her horse had shared a barn on Old Mission Peninsula with two other horses previously diagnosed with EPM after they’d become weak and stumbled on rides. Ellie also tested positive.
Reye later learned that it’s highly unusual for three out of six horses to be struck with EPM within a year of each other.
“It’s weird because it’s supposed to be very sporadic,” Reye said.
Indeed, the protozoal parasite causing EPM can be detected in a majority of horses. But only about 1 percent of horses that test positive for the parasite ever develop a clinical disease, said Shanti Bhuyan, a large animal veterinarian in Kingsley, who cited a large study.
Bhuyan called the 50 percent occurrence in one barn a “statistical glitch.” He sees 2,000 horses a year, and hasn’t seen a single case.
“I just want to make it clear that there is not an outbreak. There is no cause for alarm,” said Bhuyan.
Bhuyan wondered if the horses had poor immune systems, but Reye said two were in excellent health and relatively young, while the third horse was a rescue and in poor health.
The parasite is not contagious, but is spread by opossums when they defecate in the horse’s water, feed or hay. Opossums pick up the parasite from cats, raccoons, skunks, and other mammals. The parasite cannot be spread from one horse to another.
Reye, an area physician, wanted others to know of the EPM “cluster” because early diagnosis can save a horse’s life. The parasite is known as a master of disguise because it mimics other diseases.
“The big thing is if I didn’t know these other horses had been hit, I could have spent a bloody fortune figuring it out,” she said. “The earlier you catch it, the better off you are.”
Treatment costs about $800, takes about a month, and there is no guarantee of success. Because of the nature of the medication, a treated horse often gets worse before it improves, she said.
”Ellie is barely able to walk up a hill,” she said. “She is stumbling, she can’t turn and walk toward you. She looks like she’s drunk, and her rear end goes all over the place. Her tail goes up and down instead of back and forth.”
Reye thinks the case is worthy of study. She suspects the horses drank contaminated water at the barn. It was never flushed, but kept “clean” with goldfish. She believes the parasite built up in concentrations too high for the horses’ immune systems to conquer.
Her advice to horse owners is to keep their water and food supplies out of the reach of critters that could carry the disease.
Lisa Tadros, a Michigan State University’s College of Veterinary Medicine resident, couldn’t comment on the Old Mission cases, but said many horses are exposed to the parasite at some point in their lives, which can sometimes lead to a false positive test result. Up to 75 percent of horses will respond to treatment; a light-riding pleasure horse can still lead a relatively normal life, she said.