New equine malady probed for clues to Lou Gehrig disease


October 09, 1991|By Frank D. Roylance | Frank D. Roylance,Evening Sun Staff

When veterinarian Peter F. Radue first saw her, the 12-year-old appaloosa was trembling violently in her stall.

The horse was clearly uncomfortable. Yet she seemed bright and alert, with a good appetite.

"I initially thought it was some sort of muscular-skeletal problem involving the spine," perhaps a bone spur or pinched nerve, says Radue, of Damascus Equine Associates in Howard County.

"I treated it appropriately for that," he says, but after several weeks, there was no improvement.

Unknown to Radue at the time, the puzzling symptoms already had been noted in other horses across the Northeast by veterinarians at Cornell University in New York. Scientists there were intrigued by an apparent new equine disease. But most striking of all to them was its similarities to a devastating human killer -- amyotrophic lateral sclerosis (ALS), or Lou Gehrig's disease.

They already had launched an intensive effort to understand the illness, and to learn whether it holds any real clues for ALS researchers.

But for Radue, it was still a personal mystery. Seeking help, he sent the ailing horse to the Marion DuPont Scott Equine Medical Center in Leesburg, Va. But tests there were inconclusive.

"They made a tentative diagnosis of a protozoal infection of the spinal cord, though the signs were not typical for that disease. They treated with an antibiotic for that, and there was no improvement," Radue says.

In fact, the move to Virginia seemed to make the horse worse, and Radue feared she would lie down and die.

"I've been in an all-equine practice for the last 12 years, and I had not seen a disease that looked just like this," he says.

Until 1985, neither had John F. Cummings, a comparative neurologist at the College of Veterinary Medicine at Cornell, or his colleague, Alexander "Sandy" de Lahunta, a veterinary neurologist.

But beginning that year, they began to see more and more horses with symptoms such as those of Radue's appaloosa. Most intriguing of all was the resemblance to Lou Gehrig's disease.

ALS is a mysterious and fatal human illness that destroys nerve cells and wastes muscles. Its victims, who typically live two to five years after diagnosis, have included Gehrig, the New York Yankee first baseman; British physicist Stephen Hawking; and the late U.S. Sen. Jacob Javits, R-N.Y.

Five thousand new ALS cases are diagnosed every year in the United States and 30,000 people now have the disease, according to the ALS Association of America, which funds the Cornell research in part.

The new, still-rare horse illness has been dubbed "equine motor neuron disease," or EMND. The count of confirmed cases has climbed from 12 to 36 in the past year alone. It has been found in 10 states, including Maryland. At least 20 other suspected cases have been reported as word of the Cornell research has spread.

Marla Stevens, a Finksburg veterinarian, says she was mystified three years ago by four horses in a Baltimore-area stable afflicted, one after another, with shakes, sweats and weight loss.

"We tested the feed, hay, water. . . . All tests were negative for toxic stuff," she says. All she could offer was "basic nursing care."

All four survived, but were left weakened. In hindsight, she says, it looks like EMND.

Weight losses can reach 200 to 300 pounds as nerves die and muscles atrophy, Cummings says. Afflicted horses also display a characteristic stance, with all four feet close together under the body, which allows the horse to stand with the least muscular effort.

Scientists want to study as many cases as possible, so they can spot any revealing patterns that emerge.

A key goal will be to determine whether the equine disease is in fact a model for ALS in humans. "We're going to have to get smart and be very persistent," Cummings says, "but I think we're going to find out."

Beyond learning to treat the equine illness, scientists want to understand why its progression in horses often arrests, or stops short of killing, while ALS is almost invariably fatal in humans.

"The fact that many of these horses arrest spontaneously may, if the [ALS] model is apt, offer hope" for finding a way to halt the progression of ALS, Cummings says.

He cautions that it is risky to make comparisons between two such different species. "Yet, the nerve cells affected here in horses . . . are precisely the same ones that die in ALS," he says.

Cummings' veterinary team at Cornell includes Beth Valentine, a Johns Hopkins-trained muscle pathologist; Hussni Mohammed, an epidemiologist; Brian Summers, an Australian neuropathologist; and clinician Tom J. Divers.

Their search for patterns in the illness has been tantalizing. EMND has struck horses of many ages, breeds and uses, suggesting that it is acquired, rather than inherited.

"We're looking at everything, from a virus to poisonous plants, to various types of toxins . . . everything from wood preservatives to events in the animals' history," Cummings says.

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