Salt Lake City

Salt Lake County Encounters First-Ever St. Louis Encephalitis Virus Presence in Mosquitoes

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Published on August 21, 2025
Salt Lake County Encounters First-Ever St. Louis Encephalitis Virus Presence in MosquitoesSource: Rameshng, CC BY-SA 3.0, via Wikimedia Commons

In what marks a first for Salt Lake County, health officials have detected the presence of the St. Louis encephalitis virus in local mosquitoes, putting medical professionals and residents on alert for this rare viral brain infection. KUTV reports that the virus, which shares similarities with the more prevalent West Nile virus, has not commonly been seen in the United States, sparking new concerns regarding vector control and public health strategies in the area.

Mary Hill, SLCoHD epidemiology bureau manager, has issued a cautionary statement to health care providers, indicating, "Now that we’ve confirmed St. Louis encephalitis virus is in our local mosquito population, Salt Lake County health care providers should consider it in the differential diagnosis for patients presenting with compatible symptoms," according to ABC4. Not all those infected show symptoms, but those that do could face fever, headache, and in more severe cases, potentially life-threatening neurological symptoms, such as high fever and neck stiffness.

Reinforcing the point that the virus cannot be spread from person to person except in rare instances like blood transfusions, the Salt Lake County Health Department is ramping up efforts to curb the spread of mosquitoes and thus mitigate the risk of this and other mosquito-borne illnesses. According to KSLTV, they are deploying mosquito surveillance and control measures across the county, while also urging residents to be proactive. This includes using EPA-registered mosquito repellents and draining standing water where mosquitoes breed.