The deadly outbreak of equine herpes virus at Churchill Downs this spring threatened to limit movement of horses between racetracks during the Triple Crown series of races. Frequent travel is also common for sport horses and such an outbreak could hamper participation at major shows. A Cornell University virologist says his preliminary research indicates that vaccines containing weakened live viruses, called modified live vaccines (MLV), appear to be more effective in preventing horse herpes than other more widely used vaccines.

Klaus Osterrieder, DVM, Associate Professor of Virology at Cornell University's College of Veterinary Medicine, will present his findings on vaccine effectiveness and answer general questions on health and infectious diseases at a reception and talk for the press, horse owners, trainers and riders during the Hampton Classic. The talk is scheduled for 5 p.m. in the Barbour Rider's Tent on August 30, 2005. In addition, equine surgeon Richard Hackett, DVM, MS, and theriogenologist Robert O. Gilbert, BVSc, MMed Vet, MRCVS, will be at the show and available to the press.

Osterrieder's preliminary study compared the effectiveness of MLV vaccines to another more widely used vaccine for equine herpes. Owners and veterinarians have been wary of live vaccines because of past incidences in which a previous MLV that was incompletely weakened caused neurological disease symptoms after it was administered. The more widely used type of vaccine, called an inactivated vaccine, employs a killed virus to activate the horse's immune response.

The study found that the horses which received MLV vaccinations consistently had lower fevers, no neurological disorders and less virus in nasal fluids. One horse vaccinated with the inactivated virus and one from the control group showed mild neurological symptoms. All the horses, however, have fully recovered.

"It's important that people know that the MLV has been in use for decades, has proven to be reasonably safe, and--in my opinion--it should be the vaccine of choice, at least in non-pregnant animals," said Osterrieder.

In some 90% of infected horses, equine herpes virus type 1 (EHV-1) leads to a mild upper respiratory infection with fever, nasal discharge and fatigue for a day or two. The virus can also cause pregnant mares to abort, and in its severest form it can lead to neurological disorders, loss of coordination and even death. The virus is spread mainly by close contact between horses. Ed Dubovi, Associate Professor of Virology and Director of the Virology Diagnostic Laboratory at the Animal Health Diagnostic Center at Cornell, said that in the last four to five years, there have been more reports of the severe neurological disorder associated with equine herpes. "It appears we are seeing it with more frequency and in a larger number of horses," he said.

In addition to Pfizer, the Morris Animal Foundation has given Osterrieder a two-year grant of $110,783, and the Harry M. Zweig Memorial Fund for Equine Research (which is supported by New York state racing revenues) has given him two grants: one for $131,414 and another for $30,000. Cornell has made a substantial investment in his laboratory setup, allowing this and other research to be conducted.


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