Residents of six Washington counties were confirmed with West Nile virus infection. Benton County had nine cases, Grant had one, Klickitat had two, Spokane had two, Whatcom had one, and Yakima had 21. All but two of these people were exposed in Eastern Washington — and they may have been exposed out of state. The Whatcom County resident was exposed while camping in Eastern Washington. Some samples are still being tested.

Of the 36 people, 28 had severe disease — including encephalitis, meningitis, and/or paralysis. Eight of them had mild illness with a fever and headache. A resident of Benton County and one from Yakima County were identified through blood donor screening as having the virus, but they aren’t counted for national reporting because they didn’t have symptoms. Blood banks in the country routinely screen donations for West Nile virus. If the virus is detected, infected blood is removed from supply, and health officials are notified.

The 2009 season ended with the return of colder fall weather. During that season 71 horses, one dog, 22 birds, and 341 mosquito samples tested positive for West Nile virus. Through this testing the virus was detected in 14 counties, with Grays Harbor, Franklin, Mason, and Walla Walla counties having their first-ever West Nile detections since monitoring began in 2001.

Washington had the nation’s highest number of horses infected with West Nile virus. Nearly half of all horses infected either died from the illness or were euthanized. This season’s environmental monitoring shows the virus is firmly established in Eastern Washington and continues to spread in Western Washington.

State and local public health agencies, mosquito control districts, other state agencies, and volunteers participate in West Nile virus environmental monitoring. The state Department of Health also began using an online dead bird reporting system to help local health partners track dead bird sightings in their communities. More than 400 dead birds were reported across the state using this new online tool.

West Nile virus is a bird disease that’s spread by infected mosquitoes. The best way to reduce the chance of infection is to avoid mosquito bites. Even though cold weather has reduced the risk of mosquito bites, the state health department encourages residents to take preventive actions that are helpful in the off-season. Dump water that collects around your home and make sure gutters are cleaned and free of debris.

More information on West Nile virus in Washington ( is on the state Department of Health Web site.