Mosquitoes infected with West Nile virus have been discovered in Eastern Washington, prompting state health officials to urge that residents take precautions against the pests.

Share story

Mosquitoes infected with West Nile virus have been discovered in Eastern Washington, prompting state health officials to urge that residents take precautions against the pests.

In the past two weeks, three groups of mosquitoes from Grant and Yakima counties tested positive for the virus, signaling the start of the West Nile season in the state.

Last year the numbers spiked, with 38 people infected and one death. That followed three years with only a handful of infections. Officials are unsure whether the rising numbers last year indicate an upward trend.

“It’s too early in the season to know what to expect,” said Liz Dykstra, entomologist with the Washington State Department of Health. “But if Washington state follows what we’ve seen in other states, we could see another huge jump in the number of cases this year.”

Some neighboring states, such as Idaho, slowly progressed from just a dozen human cases in the first few years after the virus appeared in the United States in 1999. By 2006, Idaho had nearly 1,000 human cases. Other states, such as Oregon, have yet to experience a severe outbreak.

“Nationally, we’ve actually seen a drop in cases over the last several years,” said Kristen Nordlund, spokeswoman for the federal Centers for Disease Control and Prevention (CDC). “But there are pockets in the Midwest and West where we have seen an increase in cases.”

Since West Nile virus arrived in the eastern U.S. 11 years ago, it has spread west. By 2002, infected mosquitoes and animals were found in Washington state, with subsequent human infections in 2006.

People contract the virus when bitten by infected mosquitoes. Birds and horses are also highly susceptible.

The virus usually surfaces with the onset of warmer weather in the late spring and early summer. In recent years, officials typically have found infected mosquitoes in late June in Eastern Washington, where the hot, dry weather and irrigation ponds provide favorable conditions for mosquitoes.

Through the summer, the virus typically moves west across the state as temperatures rise, hitting Western Washington by August or September.

Though it’s still early in the season, the Department of Health recommends residents protect themselves against mosquitoes by using effective repellent and wearing long pants and sleeves when the insects are present.

“The bottom line is that West Nile is a preventable disease and people can take measures to avoid it by taking precautions against mosquitoes,” said Hilary Karasz, spokeswoman for Public Health — Seattle & King County.

Those measures include putting screens in windows and removing any standing water in backyards.

While most people bitten by an infected mosquito won’t get sick, one in five will have mild flulike symptoms, including fever, headache and body aches, fatigue, rash, nausea or vomiting.

Occasionally, the virus can lead to serious neurological conditions, including meningitis or encephalitis.

The Washington State Department of Agriculture is also recommending that horse owners vaccinate their horses against the virus. Last year, the state had 72 infected horses, the highest incidence in the nation. Typically, 50 percent of these animals die or need to be euthanized.

“It’s a very serious illness for a horse, and there isn’t much a vet can do after it gets sick,” said Jason Kelly, Communications Director with the Washington State Department of Agriculture.

“The best thing for a horse owner to do is to spend a few dollars and get their animal vaccinated.”

No infected mosquitoes have been found in Western Washington, and if the unusually cool weather continues through the summer, there might be fewer cases, Dykstra said.

“Or this could be our big year if Washington follows the trajectories of other states, but we’ll have to wait and see what happens.”

Cassandra Brooks: 206-464-2311 or