Two Washington residents from Pierce and Yakima counties have been infected with West Nile virus, health officials confirmed Friday.
And a suspected third case may exist in Benton County, where health officials are waiting for test results from a resident with symptoms of the illness caused by the virus.
"West Nile virus is hitting many parts of the nation hard this season, so it's not surprising we'd have cases among people in our state," Secretary of Health Mary Selecky said in a statement. "The best protection against this disease is avoiding mosquito bites. The travel-related case is a reminder to protect yourself when you travel, too."
Selecky was referring to the Pierce County case, in which a woman in her 70s likely was exposed while traveling outside of Washington.
The Yakima County case involves a man in his 30s who hadn't traveled, the state Department of Health said.
The federal Centers for Disease Control reports nearly 2,000 cases of West Nile infection in 48 states through Tuesday -- the highest number since the virus first was detected in the United States in 1999. Friday's report made Washington the 49th state to report illnesses.
About 45 percent of this year's West Nile infections have been reported in Texas, with many of the rest coming from South Dakota, Mississippi, Oklahoma, Louisiana and Michigan.
Washington's first human West Nile infection was reported in 2006, with 2009 the peak year so far for the illness when there were 38 human cases reported in 16 counties, and one death -- a 71-year-old Sunnyside woman.
Only two human cases were reported statewide in 2010 and none last year.
Most of this year's West Nile activity has been centered in Yakima County, where health officials have found four of the five virus-positive mosquito samples collected since the season started. The fifth was found in Franklin County.
A horse in Grandview was euthanized in late August after it was confirmed the 2-year-old gelding had West Nile.
West Nile virus is transmitted from mosquitoes to birds, horses and people.
Only about one in 150 people infected becomes seriously ill, but health officials recommend using bug repellent and wearing long pants and sleeves outdoors when mosquitoes are active to avoid bites. Also check for standing water around your home.
Horses can be vaccinated against the virus, but no human vaccine exists.
In humans, West Nile can cause inflammation of the brain and lining of the spinal cord. Symptoms may include fever, headache, body aches, neck stiffness, stupor, disorientation, tremors, convulsions, muscle weakness, paralysis and coma.
People with severe symptoms should contact a doctor, health officials advised.