mosquito trap file

Matthew Stott sets a mosquito surveillance trap at the American West Heritage Center in this 2017 file photo.

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One person has died and at least 11 Utah residents have been diagnosed with West Nile virus this season, according to the Utah Department of Health.

The death was reported from the Weber/Morgan Health District, and the 11 confirmed cases have been in Salt Lake, Davis and Weber counties, although the virus has been found in a high number of mosquito traps statewide.

Five additional human cases are pending confirmation.

“We could see many more Utahns become ill unless residents take steps to reduce mosquito exposure,” states Utah Department of Health vectorborne/zoonotic epidemiologist Hannah Rettler.

While most people infected with West Nile virus don’t develop any symptoms, about 1 in 150 people develop a severe illness that affects the central nervous system. Among patients with neuroinvasive disease about 1 in 10 die.

According to Rettler, “Utah is now seeing the highest number of mosquito trap sites test positive for WNV than we’ve had in the history of West Nile surveillance in the state.”

As of Aug. 23, 8% of mosquito trap sites had tested positive for the virus, 506 out of 5,906 total sites, Rettler stated. For reference, in 2020, 0.008% tested positive, and in 2017, the year with the highest number of human WNV cases (62), 8% of mosquito trap sites tested positive.

“West Nile virus is an annual presence in Utah and it isn’t going away,” Rettler states.

In addition to the human cases, nine horses have tested positive for West Nile virus, two crows, two sentinel chickens, one magpie, one scrubjay, and one red-tailed hawk.

According to Dean Taylor, Utah’s state veterinarian, precautions for horse owners are available.

“Vaccines against West Nile virus and other neurologic diseases are readily available from your veterinarian,” Taylor said. “Every owner should discuss vaccinations with their veterinarian in the spring before mosquito season.”

Owners can also protect their horses by using insect repellents, fans and screens and eliminating stagnant water sources where mosquitoes breed.

Horses become infected with WNV through mosquito bites; unlike many other diseases, infected horses do not spread the infection to other horses or people.

Utah records an average of 12 human cases of West Nile virus each year, ranging between two and 21 cases. In 2019, there were 21 human cases, and in 2020 there were two.

Taking these simple precautions to avoid mosquito bites is the best way to reduce your risk for infection.

— Wear long sleeves, long pants, and socks while outdoors and use an insect repellent with 20%-30% DEET, which is safe to use during pregnancy. Repellents are not recommended for children younger than two months of age.

— The hours from dusk to dawn are peak biting times for many mosquitoes. Consider rescheduling outdoor activities that occur during evening or early morning.

— Mosquitoes lay their eggs in standing water. Remove any puddles of water or standing water including in pet dishes, flower pots, wading and swimming pools, buckets, tarps, and tires.

— Report bodies of stagnant water to your local mosquito abatement district.

— Keep doors, windows, and screens in good condition and make sure they fit tightly.

— Consult with an immunization travel clinic before traveling to areas that may have mosquito-borne illness such as Zika or dengue and take the necessary precautions.

West Nile virus is usually transmitted to humans through the bite of an infected mosquito, but not all mosquitoes carry the virus. Symptoms of the severe form of West Nile virus include high fever, severe headache and stiff neck, disorientation, and confusion. If you are experiencing symptoms, contact your health care provider immediately.

West Nile virus surveillance will continue into early fall. You can find an updated weekly West Nile Report on the Utah Department of Health’s website,

For more information about West Nile Virus, call your local health department or visit

The Cache MAD can be reached at (435)890-9545, the Logan MAD at (435)716-9749, the College/Young Ward MAD at (435)755-5733. Visit for a full list of MADs.

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