Horses May Have Been Exposed To Once Rare Disease Oregon One Of The ‘Hot Spots’ For Condition That Causes Lameness, Blindness And Muscle Atrophy

About 45 percent of Oregon horses west of the Cascade Range may have been exposed to a once rare neurological disease, state veterinary researchers have warned.

Cases of equine protozoal myeloencephalitis, or EPM, have increased dramatically in Oregon in the past decade.

The disease can cause loss of appetite, seizures, muscle atrophy, lameness, partial paralysis, “wobbling” and even blindness.

“We don’t know for sure how bad this may get,” said Dr. Linda Blythe, assistant dean of the Oregon State University College of Veterinary Medicine. “But as a neurologist for 18 years, I’m amazed at the rapid increase in cases.

“Just in the past few years, this has become the No. 1 neurological disease of horses in the Western Hemisphere. And Oregon is one of the hot spots.”

The college randomly sampled 334 horses in 1995, finding an immune response to the EPM parasite in 149, or 45 percent, of the animals tested. The findings were reported in February in the Journal of the American Veterinary Medical Association.

Oregon cases confirmed at Oregon State have jumped from two or three a year when the disease first was diagnosed in 1986 to 38 confirmed or suspected cases in 1996. So far this year, the college is seeing a case a week.

Barbara De Noma of Scio said her 23-year-old appaloosa gelding, Handi Smoke, was quickly affected by EPM last August and still hasn’t recovered.

“He was fine and all of a sudden, boom! He walked like a drunk,” she said. “We took him to OSU for a spinal tap, and even when we got there it was worse. He couldn’t stand and used the wall to stay upright.”

Treatment with drugs still hasn’t cured the horse, although the gelding now can stand and walk.

“But he isn’t stable enough to handle a rider,” De Noma said.

The rate of horses that become ill or die remains low nationwide, less than 1 percent, as shown by studies in Ohio. Still, veterinarians are worried about the potential spread of the disease, which is expensive to treat.

EPM is caused by a single-cell parasite passed through oppossum feces into pasture grass, hay, grain and water. The disease is thought to be more prevalent in western Oregon because the parasite thrives in damp, mild climates and the oppossum population is growing.

EPM is treatable with antibiotics and immune boosters, but costs range from $600 to $2,000 for treatments that last three to six months.

“It’s a frustrating, extremely hard disease to diagnose,” Dr. Tim Phillips said.