West Nile virus cases increasing in Wyoming

SHERIDAN (WNE) — West Nile virus was first detected in mosquitos collected from Sheridan County in July. Since then, additional infected mosquitoes have been discovered in Sheridan County and surrounding areas.

Equine West Nile virus cases have been confirmed in Sheridan County and Johnson County. Human cases of West Nile virus continue to occur in other counties throughout Wyoming, most recently in Natrona County. 

Historically, the mosquito species capable of transmitting West Nile virus remains viable through the month of September.

An infected mosquito can transfer the virus during feeding. The virus can infect horses, birds, and in some cases, humans. Human cases are generally asymptomatic but can be more severe in elderly and immunocompromised individuals. 

According to the Centers for Disease Control and Prevention, symptoms can include headache, body aches, joint pain, vomiting, diarrhea and rash. Most people will recover from these symptoms completely. In some cases, fatigue and weakness can last up to several months. Anyone who is experiencing these symptoms should consult with a medical professional.

Sheridan County Public Health, in cooperation with the Sheridan County Weed and Pest Control District, encourages the public to stay mosquito safe. 

The public can take steps to protect themselves and their neighbors from West Nile virus by applying larvicide to areas of standing water. Residents should also remember the five Ds of mosquito prevention: Dump, Drain, Dress, DEET, and Dusk/Dawn. 

This story was published on August 27, 2025.