Although the Laurel Park filly that had tested positive for equine herpesvirus last week was euthanized over the weekend, more than four dozen other horses tested have come back negative for the disease, according to the Maryland Department of Agriculture.
The outbreak has led the state agriculture department and the Maryland Jockey Club to place restrictions on horse movement at Laurel Park, and it will be at least early December before operations can be back to normal, assuming the equine herpesvirus (EHV-1) does not recur.
The affected filly, a 2-year-old named Nin who was stabled in Barn 1, first exhibited symptoms Wednesday when she was unable to stand.
Although Nin's symptoms appeared to be less severe the next day, her condition was not improving and she was euthanized Saturday night.
Besides Nin, there were 25 other horses in Barn 1 and all of those animals, as well as 31 lead ponies, tested negative.
"It was especially good news that all the lead ponies were negative," said the jockey club's racing secretary, Georganne Hale, "because they come in contact with so many horses."
As a precaution, the jockey club has restricted movement of horses going in and out of Laurel Park for racing until further notice.
The only outside horses being allowed into Laurel Park are those from the Bowie Training Center and have been brought in on special shuttles.
The four-day racing schedule (Wednesday through Saturday) has continued at Laurel Park, though fields have been smaller as a result of the restrictions.
Agricultural officials must wait 21 days from the presence of the last clinical evidence (in this case, Nov. 15, when Nin was euthanized) before lifting the hold order on Barn 1 that limited the movement of horses there.
EHV-1 causes upper respiratory infection and can also cause severe neurological problems in horses but poses no known health risks to humans. In 2006, an EHV-1 outbreak that began at Pimlico Race Course and spread elsewhere in the state, including Laurel Park, resulted in six horses being euthanized.
Although the vast majority of horses are infected with a herpesvirus, often at a young age, the symptoms in young animals are mild and the virus becomes latent, according to Paul Lunn, a Colorado veterinarian who is an expert on the disease and a spokesman for the American Association of Equine Practitioners. The latent virus can be re-activated by any number of suspected causes, including stress, Lunn said.
