West Nile A Growing Threat to Horses

Equine veterinarian Dr. Christina Cable educates a horse owner about the risks of West Nile virus.

West Nile virus isn’t just a concern for people. Since its discovery in the Northeast in 1999, the mosquito-borne virus has infected over 15,000 horses across North America. Approximately one in three clinically affected horses have died or been euthanized, making West Nile one of the deadliest disease threats to horses today.

The West Nile virus cycles between mosquitoes and birds, each infecting the other. Migrating birds have helped to spread the virus northbound and westbound to nearly every province in Canada. Horses become infected when a mosquito carrying the virus bites them.

Once a horse has been bitten, it may take 5 to 15 days for signs of West Nile infection to appear. The virus attacks the brain and spinal cord causing stumbling, muscle weakness, convulsions, coma or death. Infected horses may stagger in circles or press their head against their stall. These symptoms can be confused with other serious neurological diseases of horses such as rabies and equine encephalitis, making prompt diagnosis and treatment are imperative.

Vaccination remains the best way to protect horses against West Nile virus. The WestNile – InnovatorTM vaccine, manufactured by Wyeth Animal Health, is the first West Nile virus vaccine to receive full license approval with established field efficacy and safety. Although 800,000 doses have been safely administered to horses across Canada, equine statistics indicate thousands of unvaccinated horses still remain at risk.

“Horses are infected with West Nile virus more often than humans or any other mammal,” says Catherine Martin, Equine Product Manager for Wyeth Animal Health.” Our vaccine is 95 percent effective, with aproven track record. Due to the continuous threat, it would be a disservice to the welfare of horses if people were not to vaccinate.”

Horse owners who intend to vaccinate need to move quickly. Experts say it takes time to build immunity against the virus.

“In 2003, all horses were vaccinated for West Nile virus in my practice,” says Dr. Mark Biederman of Biederman Equine Centre. “There was no incidence of West Nile in any vaccinated horses, despite the high risk in our area. I plan to continue to protect all horses with West Nile -InnovatorTM in 2004.”

Dr. Patrick J. Meyers of Meyers EquineVeterinary Services says, “Although the prevalence of the WNv disease in our horse population is not exactly known and may vary from one year to the next, I can’t imagine horse owners not wanting to protect their horses from this potentially fatal and debilitating disease. I support full vaccination of my clients’ horses.”

The U.S. Department of Agriculture’s Animal and Plant Health Inspection Service says millions of doses of West Nile vaccine have been used since the USDA granted its approval in 2001, and horse owners should be assured that the vaccine is safe. Them Ontario government also urges horse owners to continue to vaccinate against West Nile.

Previously vaccinated horses will need booster shots according to your veterinarian’s recommendation. A common practice for veterinarians, per American Association of Equine Practitioners’ vaccination guidelines, is to provide a 4-6 month WNv booster for horses traveling to or in high risk areas.

People who suspect that horses have become infected with West Nile virus should contact their veterinarian immediately. In addition to vaccination, other preventative measures recommended by health experts are the removal of stagnant water where mosquitoes can easily breed, and the use of insect repellents.

The West Nile – InnovatorTM vaccine isavailable only through a licensed veterinarian. For more information, horse owners should contact their veterinarian or visit www.wyethah.ca.


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