US counties issue West Nile virus mosquito alerts

The Lake County Health Department reported that a mosquito pool collected on June 16 tested positive for West Nile virus, marking the first confirmed presence of the virus in the county this year. Officials noted that Lake County recorded 12 human cases last year, the highest in a decade, and urged residents to follow the "4 Ds of Defense"—drain standing water, use DEET‑based repellents, protect during dawn and dusk, and dress in long sleeves.

In Contra Costa County, the Mosquito and Vector Control District announced the detection of the first West Nile‑infected mosquitoes of the season near Pacheco Marsh. The district advised the public to eliminate standing water, use EPA‑registered repellents, and report dead birds, which can signal virus activity. Both counties offer free mosquito‑control services and hotlines for reporting concerns.

Health officials emphasize that while most infections are asymptomatic, older adults and those with weakened immune systems are at greater risk of severe illness, including meningitis or encephalitis.