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West Nile Virus is back in Tennessee. The Tennessee Department of Health confirmed on June 9 that a crow from Hamilton County tested positive for WNV.

Dr. Frederick Harper, a horse specialist with the University of Tennessee Agricultural Extension Service, said horse owners should keep a close watch over their animals. “In 2002 about six weeks after the appearance of the first positive WNV bird, positive WNV horses were identified,” he said.

Mosquitoes become infected with the virus when they feed on infected birds. They can then transmit the virus when they bite humans and horses. “Horses are not a source of the virus for mosquitoes,” said Harper.

There were 148 positive WNV equine cases in Tennessee in 2002 with 42 deaths. Most of these were reported in late summer or early fall.

Harpers says that horses vaccinated in 2002 for WNV should already have been given a booster. The WNV vaccine has been demonstrated to be 94 percent to 98 percent effective, but Harper cautions owners to reduce the risk of exposure to mosquitoes by eliminating mosquito breeding areas around their horse facilities.

“Horse owners who have not vaccinated their horses need to do so at once by giving the initial shot in the two-injection series. The second injection is given 3 to 4 weeks after the first. It takes about 3 to 4 weeks after the second injection for the horse to have protective immunity,” Harper said.

Pregnant mares should not be vaccinated in their first trimester, and it may not be advisable to vaccinate them in the second trimester. “Foals from unvaccinated mares or mares not given a booster 4 to 6 weeks before foaling should be given a three-injection series starting at 3 months of age. Foals from mares given a booster within 2 months of foaling should be started on a three-injection series at 4 to 6 months of age. There should be 3 to 4 weeks between the first and second injections and 6 to 8 weeks between the second and third injections. Some foals will be in these age ranges now,” he said.

Horses with WNV lack muscular coordination and have difficulty in moving and standing. More information about the disease, including additional symptoms and the current WNV vaccination protocol, is available online at the UT Department of Animal Science West Nile Virus Web site: http://animalscience.ag.utk.edu/. Click on “horses” under Extension Programs.

The public can keep up to date on WNV in humans as well as birds and equines by periodically checking the state WNV report online at http://www2.state.tn.us/health/CEDS/wnvhome.htm. County by county summaries are available.

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Contact: Dr. Frederick Harper, 865-974-7295; Patricia McDaniels, 865-974-7141