West Nile virus found in Clovis mosquitoes, Fresno County monitoring

West Nile virus has turned up in Clovis mosquitoes for the first time this year, pushing Fresno County’s 2026 mosquito season from surveillance into action as public health crews watch for spread near homes, parks and summer youth activities.

District Manager Jodi Holeman confirmed the first positives during the week of June 4, and the Consolidated Mosquito Abatement District said it is monitoring the area closely. The district did not identify a school, park or specific neighborhood in the public update, but it warned residents not to assume a block is safe simply because no positive mosquitoes have been trapped nearby.

The Clovis detection came after Fresno County’s first West Nile signal of the year showed up in a dead bird, part of an early statewide pattern that has included four West Nile-positive dead birds in four counties, Alameda, Fresno, San Diego and Santa Clara. As of the latest California update, no human West Nile infections had been reported in 2026.

The California Department of Public Health says West Nile is the most common and serious mosquito-borne disease in California, spread by infected mosquitoes, especially Culex mosquitoes, and most often transmitted during summer and early fall. The agency says about 4 in 5 infected people never show symptoms, while about 1 in 150 develop severe illness. People age 55 and older face the highest risk of serious disease.

In Fresno County, the mosquito district says West Nile and St. Louis encephalitis can begin circulating when average daily temperatures reach 75 degrees, a threshold that makes warm evenings and irrigated yards especially important. The district uses an integrated mosquito management approach and can move to adulticide ULV treatments when disease is detected or mosquito numbers climb. One adult mosquito treatment was already scheduled for May 7 in Fresno County.

Holeman pointed to the district’s earlier work with Verily from 2017 to 2019, saying the mosquito-release project achieved “upwards of 95% suppression” of wild mosquito populations. That history gives local officials a benchmark as they confront this season’s first Clovis positives and try to keep the virus from gaining a foothold.

For residents, the message is immediate: use insect repellent, especially at dawn and dusk, and dump standing water around homes where mosquitoes can breed. In a season that has already produced Fresno County’s first dead-bird detection and now its first positive mosquitoes in Clovis, officials are treating this as the point to tighten prevention, not wait for a human case.