First human infection of West Nile virus in Idaho this year

DHW Communications

Idaho’s first human West Nile virus (WNV) infection this year was identified in a Washington County resident over the age of 50 on Thursday, Aug. 3. This person has been hospitalized with the infection but is recovering and being discharged home. So far this year, WNV activity in mosquitoes has been detected in nine Idaho counties, seven of them in south and southwestern counties. WNV has also been detected in mosquitoes in neighboring Malheur County, Ore.

WNV is spread by the bite of an infected mosquito and can lead to severe disease in some people.

“We strongly encourage Idahoans to fight the bite of mosquitoes to protect themselves and their families,” said Dr. Leslie Tengelsen, state public health veterinarian. “Confirmation of a human infection is a good reminder for all of us to take protective measures against mosquito bites. This includes wearing insect repellent and protective clothing in addition to reducing standing water around our gardens and homes where mosquitoes can lay their eggs.”

Symptoms of WNV infection often include fever, headache, body aches, nausea, and sometimes swollen lymph glands or a skin rash. Infection can result in severe illness, especially in people 50 years or older, leading to hospitalization and even death. Talk to your healthcare provider about testing for WNV to confirm your illness.

Last year, three human WNV infections were reported statewide. WNV activity in mosquitoes, horses, or people was reported in seven counties. WNV infections that might be reported each year are difficult to predict as some cases might not seek testing, but in the last five years, 11 cases have been reported each year, on average.

To protect against WNV infection, people should avoid mosquitoes, particularly between dusk and dawn when mosquitoes are most active. In addition, everyone should:

  • Cover up exposed skin when outdoors and apply DEET or other EPA-approved insect repellent to exposed skin and clothing. Carefully follow instructions on the product label, especially for children.
  • Insect-proof your home by repairing or replacing damaged screens. 
  • Reduce standing water on property.Check and drain toys, trays or pots outdoors that can hold water.
  • Change bird baths, static decorative ponds, and animal water tanks weekly to reduce suitable mosquito habitats.

WNV does not usually affect domestic animals, like dogs and cats, but can cause severe illness in horses and some species of birds. Although there is no vaccine for people, there are several vaccines for horses, which should be vaccinated annually.

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Southwest District Health is one of seven public health districts throughout Idaho established to protect and promote the health and wellness of those who live, work, and play in our region. We proudly serve Adams, Canyon, Gem, Owyhee, Payette and Washington Counties. We work in partnership with our community to identify health needs, design solutions, and implement services that encourage behaviors contributing to healthier, longer lives. Learn more at