Ask an Expert – Safeguarding Against West Nile Virus

By Alexander Knudson | September 1, 2023



Many areas of Utah are experiencing higher mosquito populations this summer due to the extremely wet winter and late summer precipitation. Increased numbers of mosquitos bring the possibility of being bitten by a mosquito infected with West Nile virus. One human virus case was reported from Uintah County this year, with several non-human detections in west central counties. Mosquitos have recently tested positive for West Nile virus in Box Elder County and Salt Lake City.  

West Nile virus is spread through the bite of mosquitos of the genus Culex. Mosquitos lay eggs in fresh stagnant water, including man-made pools, ditches, and marshy areas, with thousands of mosquitos developing in seven to 10 days. Adult females feed on birds, people, and other animals to produce eggs. Blood feeding is when transmission occurs. Wild birds are considered reservoir hosts, meaning the birds can infect more mosquitos. People and other animals cannot re-infect mosquitos. 

About 80% of people do not develop symptoms when infected with West Nile virus. But the 20% who do may experience headaches, body aches, joint pain, vomiting, diarrhea, or a rash. Fewer than 1% of people infected will develop neurological illnesses such as encephalitis or meningitis. Horses can be infected with the virus, and unfortunately, the infection could be fatal to them. 

To prevent being bitten by an infected mosquito, consider these tips: 

* Reduce larval habitat by emptying water-holding containers and basins. 

* Be sure home windows have screens to prevent mosquitos from entering. 

* Avoid areas with high mosquito populations, and be especially vigilant during the peak mosquito activity times of dawn and dusk. 

* Use insect repellents that contain Deet, Picardin, or other EPA-approved repellents as directed. 

* If you are also using sunscreen, apply sunscreen first and insect repellent second for best results. 

* Cover up. Wear loose-fitting clothing such as long-sleeved shirts and pants, and protect your feet by wearing shoes and socks. 

* Treat your clothes with 0.5% Permethrin (an insecticide) if spending time in areas with high mosquito populations.  

Further information about West Nile virus can be found on these websites:

Utah Department of Health and Human Services for data regarding West Nile virus, and

West Nile virus mosquito and animal activity map by county, Utah, 2023.

Centers for Disease Control and Prevention for general information about the virus.

Utah County Health Department for details on protecting horses from West Nile virus. 

By: Alexander Knudson, Utah State University Extension arthropod diagnostician