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West Nile virus cases in Wyoming hit 10-year high in 2023

A close up of a mosquito biting someone.

The number of West Nile virus cases in Wyoming last year was the highest in about a decade, according to recently released data from the Wyoming Weed and Pest Council. Officials are pushing regions to do more testing and abatement, and share prevention tips as adult mosquitoes that may be carrying the virus emerge.

Last year, there were human and animal cases in all but two counties. Wyoming Department of Health (WDH) data show there were 27 human cases and four reported deaths. That’s a sharp increase over 2022, when the WDH reported just three human cases.

“It kind of took people by surprise in Wyoming,” said Mikenna Smith, president of the Wyoming Mosquito and Vector Management Association. “We never really know when these outbreaks are going to occur. West Nile virus is one of the most difficult vector borne diseases to predict or to model.

The Association trains mosquito districts on how to trap mosquitoes carrying the West Nile virus and prevent their spread. Some districts are operated by cities or counties. 

“We’ve been out dipping for mosquito larvae and we’re finding some pretty significant quantities,” said Brian Songer, assistant supervisor for the Sheridan County Weed and Pest District. “We bring them back to our office and watch their development daily and try to determine when the adults will start hatching.”

Livestock are also susceptible to the virus. Horses can be vaccinated against it. Even so, about 50 cases of equine-related West Nile virus were documented last year, again a sizable increase over the year prior.

“We are very concerned that the trend will continue and that’s why we’ve ramped up our program, trying to get out and predict where the mosquitos are and make our larval treatments more effective,” Songer said.

Smith says a lot of mosquito habitat, which includes just about anything that can hold water for five to seven days, in Wyoming is found on private lands.

“I always encourage ranchers if they are flood irrigating to keep their water moving, not letting it stagnate in one area for more than seven days,” she said.

Smith also encourages people to wear long-sleeved clothing and EPA approved repellent, and to be especially careful during the dawn and dusk hours when mosquitoes like to feed.

The Wyoming Weed and Pest Council is advising folks to prepare themselves for mosquito season and is offering tips that can help protect your family and cut down the number of mosquitoes that carry the virus.

  • Take time to minimize standing water sources on or near your property. It could be buckets, old tires, or anywhere that puddles form. According to Songer, “it could be as small as a water bottle cap or as large as a cattail swamp area.” Also minimize stagnation of irrigation waters by avoiding over-irrigating on saturated soils and by draining pastures of excess water. Ensure irrigation structures are in good working order and remove any blockages in ditches and culverts. Keep water from collecting in low-lying areas
  • Protect yourself from exposure to bites. Mosquito-proof or long sleeve clothing can be effective at keeping the bugs at bay, as can treating boots, pants, and socks with EPA-approved repellant. If you are unsure of what repellent to use, the EPA has a useful guide on their website to help you choose.
  • Be sure to protect infants and children by covering their arms and legs. If using repellent, make sure the ingredients are suitable for children and apply using your hands, avoiding eyes, mouths, cuts, and the child’s hands. If using sunscreen, apply before spraying repellent. 
  • For horse owners, be sure to get your horses vaccinated for WNV in the spring. Ensure the horses are turned in at dusk and dawn which are the times when mosquitos are most active. Fans and sprays are also effective deterrents.
  • Be on the lookout for the symptoms of West Nile Virus. According to the CDC, most people do not experience any symptoms. However, some people may experience a fever, headaches, joint pains, vomiting, diarrhea, or rashes. If you think you or a family member have contracted West Nile Virus, contact your doctor. Contact the WWPC if you or an animal on your property is diagnosed to help guide surveillance and treatment efforts
Olivia Weitz is based at the Buffalo Bill Center of the West in Cody. She covers Yellowstone National Park, wildlife, and arts and culture throughout the region. Olivia’s work has aired on NPR and member stations across the Mountain West. She is a graduate of the University of Puget Sound and the Transom story workshop. In her spare time, she enjoys skiing, cooking, and going to festivals that celebrate folk art and music.

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