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First St. Louis Encephalitis Virus Found in Salt Lake Mosquitoes

8/21/2025

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Summary

Story summary

Salt Lake County health officials confirmed the first detection of St. Louis encephalitis virus (SLEV) in local mosquitoes since 2003.
SLEV is rarer than West Nile virus, with 307 U.S. cases since 2003 and no fatalities in Utah.
Symptoms include fever, headache, and nausea; severe cases may cause long-term disability.
Health officials advise preventive measures against mosquito bites, as no vaccines or treatments are available for SLEV.
Previous SLEV detections occurred in southwestern Utah in 2022 and 2023, and in Millard County in 2024.

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Story summary

Salt Lake County health officials confirmed the first detection of St. Louis encephalitis virus (SLEV) in local mosquitoes since 2003.
SLEV is rarer than West Nile virus, with 307 U.S. cases since 2003 and no fatalities in Utah.
Symptoms include fever, headache, and nausea; severe cases may cause long-term disability.
Health officials advise preventive measures against mosquito bites, as no vaccines or treatments are available for SLEV.
Previous SLEV detections occurred in southwestern Utah in 2022 and 2023, and in Millard County in 2024.