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For Immediate Release - April 21, 2004

Vaccinate Horses for West Nile Virus

With the rather cool spring weather, horse owners are likely not thinking about mosquitoes. University of Tennessee horse specialist, Dr. Frederick Harper, says they should be.

Mosquitoes are the carriers of West Nile Virus (WNV) to horses. It is critical that horses, mules and donkeys are vaccinated for WNV before the mosquito season, which begins at different times across the state.

There were 103 positive WNV cases in horses in Tennessee in 2003. Of these, 17 horses died or were euthanized. These numbers have decreased since 2002, when 150 horses tested positive for WNV and 42 died or were euthanized.

In 2002, the majority of WNV cases occurred in West Tennessee. Last year, most cases of positive WNV horses were in East Tennessee. The decrease in the incidence of horses with WNV and the death rate is not a reason to skip horse vaccination in 2004.

Horses, mules and donkeys in all regions of Tennessee are at risk and should be vaccinated, says Harper.

Horses not previously vaccinated require two initial injections given three to four weeks apart. It takes another three to four weeks for the horse to acquire immunity.

Equine vaccinated in 2003 require an annual booster. This booster should be given before the mosquito season, the equine specialist says.

Two licensed WNV vaccines are available as prescription drugs from veterinarians. Previously, there was only one WNV vaccine for horses. The protocol for either vaccine is similar as both require two initial injections followed by an annual booster.

If you have questions about which brand of WNV vaccine to use, contact your veterinarian. No matter which vaccine you use, it is imperative to have horses vaccinated for West Nile Virus, says Harper.

For additional and current WNV information, visit the UT Animal Science WNV Web site at



Dr. Frederick Harper, 865-974-7295
Samantha Hill or Patricia McDaniels, 865-974-7141



Institute of Agriculture Experiment Station Extension College of ASNR College of Veterinary Medicine