Washington State led the nation in confirmed West Nile cases in 2008, with Yakima County reporting the most cases. Ten cases were found in Grant County; four in Benton County, and one horse tested positive for the virus in Kittitas County, reports the Washington State Department of Agriculture.

Highlighting the importance of vaccinations, almost all the infected horses were not vaccinated. West Nile is fatal in about one third of non-vaccinated horses. 

"Vaccinating your horse or getting proper booster shots is the best way to help protect your animal, and prevent greater expense of treating the horse after the disease is acquired," warns Washington State Veterinarian Leonard Eldridge.

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

The Washington Department of Health reports that 3/4 of tested mosquitoes in Yakima County tested positive for the virus.

California has the second highest number of cases, followed by Texas.