After one horse at The Meadows harness racing track died of the highly contagious and nearly always fatal disease equine herpes, about 30 other horses have been put under quarantine for 21 days.

Only the trainers and veterinarians of those horses, which were quarantined Feb. 18, are permitted in the barn, and they must enter and exit through a decontamination wash. A treadmill has been brought into the barn to exercise the horses.

The Washington County harness track is the third site in North America to have a horse or horses stricken this year with the neurological strain of the illness, which affects the spine, leaving a horse unable to stand. The last outbreak in Pennsylvania was at Penn National near Harrisburg in 2003, according to Dr. Lawrence Soma of the University of Pennsylvania School of Medicine, New Bolton campus.

The others affected this year were tracks in Canada's Maritime Provinces and Northville Raceway in Michigan. The latter was forced to close for racing for several days after four deaths mandated the quarantine of multiple barns, leaving the track without enough horses to fill a program.

General manager Drew Shubeck said yesterday he is confident it will not come to that at The Meadows. The track is already eight days into the quarantine with no new cases reported, and it has about 900 horses on the grounds. Northville has several hundred fewer horses than The Meadows.

"We're hoping this is the end of it," Shubeck said.

The incident began Feb. 17 when Twilight Mystery, trained by Jeff Indof, was scratched sick out of a race.

The next morning the horse was down in his stall and couldn't get up. Veterinarian Dr. Josh Hunter diagnosed equine herpes, and Twilight Mystery was euthanized.

His body then was sent to New Bolton for an autopsy last Saturday, and three pathologists were assigned "because of the importance of making a correct diagnosis," said Soma, the go-between for New Bolton and the Pennsylvania Harness Racing Commission.

"They made the diagnosis on gross observation of the spinal cord and other parts of the horse," Soma said. They also did histological slides of tissue, and those test results came back confirming the diagnosis on Tuesday.

The rest of the barn was put under quarantine immediately after Twilight Mystery was euthanized. Trainers affected besides Indof include Kris and Wayne Hite, Ray Paver, and Naquel Harvey, who has just one horse in the barn.

The disease is transmitted by close contact with a horse or human contaminated with herpes or in contact with contaminated surfaces.

"If someone is hands-on with [the virus], he can transmit it to the horse. It can be hand to mouth or nostrils or contaminated surfaces like the stall," Soma said. The incubation period is seven days, but experts advise quarantining through three incubation cycles.

The first symptom of the illness usually is a spiked temperature, but Twilight Mystery never showed that symptom, Soma said. Nevertheless, vets are taking the temperatures of the quarantined horses twice a day, using a new pair of gloves for each horse.

In addition, Shubeck said, the rest of The Meadows horse population is being monitored for symptoms, and trainers have been having their horses immunized against the disease.

"This weekend tells the tale," Shubeck said. "If there are none sick by Monday, I'll feel a pretty good comfort level. I think what we did was sufficient. We are racing as normal with the quarantine in place."