Mosquito pool testing in state shows increase in West Nile virus


Photo courtesy of Wyoming Department of Health

Press Release

August 11, 2023 — With human cases in nearby states and a higher-than-usual number of mosquito pools within Wyoming testing positive for West Nile virus, the Wyoming Department of Health (WDH) wants people to remember to protect themselves from mosquito bites.

“Wyoming’s reported human West Nile virus case numbers have been quite low the past several years,” Courtney Tillman, an epidemiologist with the WDH, said. “But with more positive mosquito pools being reported this summer than we have seen in nearly ten years and cases popping up in neighbor states, a reminder to avoid these insects may be timely.”

West Nile virus first appeared in Wyoming in 2002. Reported annual human cases have ranged from one with no deaths last year to 393 and nine deaths in 2003. It is spread by mosquitoes when they feed on infected birds and then bite people, animals, or other birds.

While most people infected with WNV don’t have symptoms, among those who become ill, symptoms include fever, headache, body aches, skin rash, and swollen lymph nodes. A very small number of individuals develop West Nile neuroinvasive disease with symptoms such as severe headache, fever, neck stiffness, stupor, disorientation, coma, tremors, convulsions, and paralysis.

“Dodging mosquito bites is the basic strategy and remains important,” Tillman said.

The “5 D’s” of West Nile virus prevention include:

1) DAWN and 2) DUSK – Mosquitos prefer to feed at dawn or dusk, so avoid spending time outside during these times.
3) DRESS – Wear shoes, socks, long pants, and a long-sleeved shirt outdoors. Clothing should be light-colored and made of tightly woven materials.
4) DRAIN – Mosquitos breed in shallow, stagnant water. Reduce the amount of standing water by draining and/or removing.
5) DEET – Use an insect repellent containing DEET (N, N-diethyl-m-toluamide). When using DEET, be sure to read and follow label instructions. Picaridin (KBR 3023) or oil of lemon eucalyptus can also be effective.

Information from WDH about the West Nile virus can be found at

Certain birds, such as crows, ravens, jays, raptors, owls, and sage grouse, are particularly susceptible to the West Nile virus. Any questions/concerns about wild birds should be directed to a local Wyoming Game and Fish Office or to the Wyoming Game and Fish Department’s Wildlife Health Laboratory at (307) 745-5865.