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State veterinarian renews call to horse owners to vaccinate against West Nile virus

OLYMPIA — Horse owners should plan to protect their livestock from West Nile virus—a potentially fatal disease in horses—particularly since Washington led the nation the past two years for equine cases of the disease.

West Nile virus (WNV) is spread by mosquitoes that have fed on an infected bird. The disease can sicken people, horses, many types of birds and other animals. It is not spread from horses to other animals.

Six counties accounted for 72 horses testing positive for WNV in 2009, up from 41 confirmed cases in 2008. This includes 23 horses in Benton County, 17 horses in Yakima County, 16 horses in Kittitas County, 11 horses in Grant County, three horses in Franklin County and two horses in Adams County. Western Washington reported no equine cases, although six dead birds tested positive.

"Nearly half of the horses infected last year either died from the illness or had to be euthanized," said State Veterinarian Dr. Leonard Eldridge. "Our state had nearly one-third of all the confirmed WNV horse cases in the U.S. last year. It's a shame that unvaccinated horses continue to be one of our most active indicators warning us that the virus is present in a local community. Clearly, WNV is an ongoing threat."

Eldridge said that the majority of WNV cases in horses are preventable with vaccination. There was only one confirmed case last year in which a horse had received the vaccine but still was sickened by WNV. That horse suffered mild WNV symptoms before recovering quickly.

Most horses acquiring WNV do not become ill and show no symptoms at all. Those that do become ill display loss of coordination, loss of appetite, confusion, fever, stiffness and muscle weakness, particularly in the hindquarters.

"Some horses go down and never get up," Eldridge said. "Others seem to fight the virus."

Although the first confirmed case of WNV in a horse last year wasn't reported until late July, there is no guarantee it will take that long for it to show up again, according to Eldridge.

Vaccinating a horse or getting the proper booster injections is the best way to help protect the animal and prevent greater expense from treating a horse infected by the disease.

"A spring dose of vaccine, even in previously vaccinated horses, is necessary to maintain protective immunity in most horses," Eldridge said.

Horse owners should consult with their veterinarian for vaccination recommendations and WNV control measures. The vaccine requires two doses the first year of vaccination two to four weeks apart. Immunity will not be achieved until three to five weeks after the second vaccination, so it's important to avoid waiting until mosquito season is in full swing.

The state veterinarian also recommends that horse owners take measures to reduce mosquito populations. Recommendations include:

•  Removing standing water from yards and barns
• Removing old tires and garbage that may be rain soaked
• Changing water at least weekly in troughs or bird baths
• Keep horses in stalls or screened areas during the early morning and evening hours when mosquitoes are the most active and feeding.

Veterinarians who learn of potential WNV cases in horses or other animals should contact the State Veterinarian's Office at (360) 902-1881.

State and local health departments, mosquito control districts, other state agencies and volunteers work together on environmental monitoring and prevention measures for the virus. Additional information on WNV can be found at the state Department of Health Web site (www.doh.wa.gov/WNV).

Note: The U.S. Department of Agriculture's Animal and Plant Health Inspection Service maintains a Web site showing states with West Nile virus equine cases in 2009 and earlier years.

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