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State veterinarian urges vaccination of horses for West Nile virus

OLYMPIA – Although the first confirmed case of West Nile virus (WNV) in a Washington state horse didn’t occur until August last year, there is no guarantee it will take that long for WNV to show up in the 2007 mosquito season, the state veterinarian said today. Six positive cases of WNV in horses were reported last year.

Dr. Leonard Eldridge is urging horse owners to vaccinate their horses against WNV as soon as possible. He also is recommending that horse owners take preventive measures to reduce opportunities for mosquitoes infected with the virus to bite horse populations.

WNV is fatal in 30 to 40 percent of all horses that contract it, although most horses do not become ill and show no symptoms at all. A horse’s physical condition and general health can determine its ability to recover. Those that do become ill show signs such as loss of coordination, loss of appetite, confusion, fever, stiffness and muscle weakness, particularly in the hindquarters.

“Older, sick or weak horses have much less chance of survival if infected,” Eldridge said. “Vaccinating your horse or getting the proper booster shots promptly is the best way to help protect your animal and prevent greater expenses from treating your horse after the disease is acquired. A spring dose of vaccine, even in previously vaccinated horses, is necessary to maintain protective immunity in most horses.”

Eldridge recommends owners take precautions on their property such as removing standing water from yards and barns and changing water in troughs or bird baths that could be a source of mosquito breeding.

The vaccine requires two doses four to six weeks apart, and immunity will not be achieved until five weeks after the second vaccine. An annual booster shot should be considered prior to the start of the mosquito season.

West Nile virus is spread by the bite of an infected mosquito and can infect people, horses, many types of birds, and other animals. Humans cannot contract West Nile illness through contact with an infected horse and infected horses do not spread the disease. Mosquitoes get infected when they feed on an infected bird.

Eldridge urges horse owners to work with their veterinarians for advice on WNV and other health issues. Veterinarians who learn of potential WNV cases in horses or other animals should contact the State Veterinarian’s Office at (360) 902-1881.

Information on WNV, including prevention measures, is available on the following Web sites:

• Department of Agriculture: http://agr.wa.gov/FoodAnimal/AnimalHealth/Diseases/WestNileVirus/default.htm
• Department of Health: www.doh.wa.gov/WNV
• Washington State University: www.wnv.wsu.edu

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