Health officials say two people in Washington state have contracted West Nile virus, while the discovery of the West Nile virus in two counties in East Oregon has triggered a seek-and-destroy mission for adult mosquitoes in the 274 square-mile North Morrow Vector Control District.
The infections are the first human cases since 2010. State officials said Friday that a Pierce County woman in her 70s was likely exposed to the virus while traveling out of state, but a Yakima man in his 30s hadn't left the state.
Their test results were confirmed at the Washington State Public Health Laboratories.
Last year, five mosquito samples tested positive, but there were no human or horse cases, and no dead bird detections. In 2010, there were two human cases in Washington, as well as detections in two dead birds and more than 100 mosquito samples. There were 38 human cases of West Nile virus in 2009 in Washington state, including the only known death from the disease in the state.
The East Oregonian reports surveillance is conducted on problem areas weekly, which are then treated with pesticide.
Two August discoveries of the virus touched off the decision to seek adult mosquitoes. The control district usually focuses on eliminating mosquito larva.
Traps armed with dry ice produce carbon dioxide, attracting mosquitoes into a net, where they are held until their species can be identified.
Only certain species can carry West Nile, so disease-carrying species are sent to the Oregon State University Veterinary Diagnostic Lab for testing.
The last time the virus infected the area was in 2009.