Public-health officials in at least five U.S. counties have reported the first signs of West Nile virus activity this year, underscoring the start of the 2025 mosquito season. In Colorado, Boulder and neighboring Weld counties said mosquitoes trapped in Niwot and other locations tested positive for the virus during the week of 8 July. The detections are the first in the state this year. Illinois followed on 9 July, with McLean County’s health department confirming its initial West Nile–positive mosquito pool of 2025. Texas is seeing a wider range of activity. Fort Bend County verified its first infected mosquito sample, collected in Katy’s 77494 ZIP code, and began evening spray operations on 9 July that are scheduled for three consecutive nights. While Fort Bend has no human infections so far, Williamson County reported its first human case, a resident in their 40s diagnosed on 3 July with neuroinvasive disease. Alabama’s Mobile County later logged the year’s second human infection in the county, according to Health Officer Dr. Kevin Michaels. Authorities in all affected areas urged residents to drain standing water, use EPA-approved insect repellents and wear long sleeves at dawn and dusk to curb further transmission.