First cases of West Nile virus in horses reported in Washington

Jul 31, 2009
by WLJ

Washington topped U.S. in 2008 with 41 horses testing positive for the virus.

West Nile virus (WNV), a potentially fatal disease in equines, has been confirmed in two horses, one in Toppenish and the other in Prosser, the Washington State Department of Agriculture (WSDA) announced last week. Neither horse was vaccinated for WNV. An 8-year-old Quarter Horse mare in foal in Toppenish, WA, was euthanized. The Prosser, WA, horse, a 9-year-old Quarter Horse gelding, is expected to recover.

These are the first confirmed cases this year of horses contracting WNV in Washington. The Animal Disease Diagnostic Laboratory in Pullman, WA, reported the positive test results to WSDA last week. The lab is operated by Washington State University. 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.

Washington led the nation last year in confirmed cases of WNV with 41 horses testing positive: 26 horses in Yakima County; 10 in Grant County; four in Benton County; and one horse in Kittitas County. In previous years, WNV horse cases have been detected in western Washington as well. Nearly all of the horses that acquired West Nile virus last year were not current with vaccinations.

WNV is fatal in about onethird of all horses that show clinical signs, although most horses 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.

“Vaccinating your horse or getting the proper booster shots is the best way to help protect your animal and prevent greater expense from treating your horse after the disease is acquired,” said state veterinarian Dr. Leonard Eldridge. “An annual booster dose should be administered prior to the start of the mosquito season.”

Horse owners should consult with their veterinarians 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 first case in 2008 for a horse was confirmed in August.

The state veterinarian also recommends that horse owners take measures to reduce mosquito populations. Precautions include removing standing water from yards and barns and regularly changing water in troughs or bird baths that could be a source of mosquito breeding.

Veterinarians who learn of potential WNV cases in horses or other animals should contact the state veterinarian’s office at (360) 902-1881. — WLJ