West Nile virus has sickened 36 people in Washington so far this year, including nine people in Benton County.

The state Department of Health said this year has been the worst on record for the virus.

A Yakima County woman in her 70s is the state’s first death from the virus, state officials said. In all, Yakima County had 21 confirmed cases.

Grant County had one, Klickitat County had two, Spokane County had two and Whatcom County had one.

All but two of them were exposed in Eastern Washington — and they may have been exposed out of state.

Of the 36 people, 28 had severe symptoms, including encephalitis, meningitis or paralysis.

Eight had mild illnesses with a fever and headaches. A person in Benton County and another in Yakima County didn’t know they had the virus until they went to donate blood and it was found in a prescreening test.

Those cases don’t count in national reports because the victims didn’t have symptoms, the state said.

Also this year, 71 horses, one dog, 22 birds and 341 mosquito samples tested positive.

That testing showed the virus was detected in 14 counties, with Franklin, Walla Walla, Mason and Grays Harbor counties having their first cases since monitoring began in 2001.

Washington had the nation’s highest number of horses infected, the state said.

Nearly half of all the infected horses either died from the illness or had to be euthanized.

The state Department of Health also began using an online dead bird reporting system to help track dead bird sightings. More than 400 dead birds were reported this year.

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, say health officials.