The Latest West Nile Virus Update

Twenty-one of the cases of West Nile virus (WNV) in horses were handled and treated by the Mattituck-Laurel Veterinary Hospital, in Laurel, N.Y. Of those 21, eight have died or were euthanized. An additional horse, a Thoroughbred, might be euthanized tonight, following intensive exam by the United States Department of Agriculture.

John E. Andresen, DVM, is the equine specialist at the animal hospital, which he co-owns with Charles Timpone, DVM. Andresen's practice includes several thousand horses which are active in many disciplines of equine sport.

Victims of the disease have had little in common in terms of age, type, or body size. Some of the horses involved were members of the following breeds: Appaloosa, Arabian , Dutch Warmblood, Palomino, Percheron, Standardbred, and Thoroughbred.

All cases of WNV were discovered within a four-mile radius of one another in several facilities near Jamesport, Long Island. The area, as described by Andresen, is fairly isolated--located far from New York City where the outbreak occurred in humans, and from Belmont Park, where there is a large population of horses that potentially could be affected by the virus.

Initially the horses all showed signs of neurologic disease. The first two horses that died due to WNV symptoms were neither autopsied nor tested for EPM. However, EPM was found in the cerebrospinal fluid of five of the six remaining dead horses. The sixth also might have been positive for EPM. However, according to Andresen, the horse was not tested for that disease as Andersen was, by that time, positive that the disease in question was WNV. There is speculation that the EPM might have weakened the horses' systems, making them more vulnerable to the effects of WNV.

Strong EPM treatment was prescribed, first with dexamethasone and Banamine, then in the form of sulfadiazine and pyrimethamine. Toltrazuril, imported from Canada and used with permission from the USDA, also has been administered. Upon discovery of WNV, the EPM treatment was continued as "they're both treated the same," along with strong anti-inflammatory medication.

Additional supportive therapy has been given through stomach-tubing of nutrients and catheterization of fluids to the horses' systems. The surviving horses are recovering in different degrees--some are getting better right away whereas others need more extensive treatment.

Andresen claims one of  Long Island's greatest concerns now is how the disease arrived. There is speculation that the disease had been present in the area already, and its effects just recently became evident. He expects the prevalence of WNV will subside in another week or two.

Andresen believes the action of Hong Kong's limiting transport of horses from the United States was unnecessary. "A horse can spread Venezuelan encephalitis. However, in Eastern, Western, and, in this case, West Nile encephalitis , the horse is not a vector, but a dead-end host. Birds are the reservoir. (The virus) then moves from mosquito to man, or mosquito to horse or other species," he says.

Since a common factor in all but one of the 21 horses was an evening turnout schedule, horse owners have been advised to bring their horses in at night to avoid the mosquito activity. The cool night air presents a problem until the first killing frost. However, mosquitos might come inside for the warm barn air as well, and residents of LI are, therefore, advised to fog the barns with repellent, and use topical repellent on their horses.

In the meantime,beyond precautionary measures, all residents can do is hope for the arrival of a killing frost to eliminate the adult mosquito population.

About the Author

Stephanie L. Church, Editor-in-Chief

Stephanie L. Church, Editor-in-Chief, received a B.A. in Journalism and Equestrian Studies from Averett College in Danville, Virginia. A Pony Club and 4-H graduate, her background is in eventing, and she is schooling her recently retired Thoroughbred racehorse, Happy, toward a career in that discipline. She also enjoys traveling, photography, cycling, and cooking in her free time.

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