University of California Agriculture and Natural Resources released information on Mar. 22 about the risks of mosquito-borne illnesses and strategies for prevention as mosquito season begins in California.
The guidance comes as warming temperatures and standing water from a wet winter create favorable conditions for mosquitoes, which can transmit diseases such as West Nile virus, dengue, yellow fever, Zika, chikungunya, encephalitis, and dog heartworm. The organization highlights that mosquitoes are considered the most dangerous animal globally due to their role in spreading disease.
According to Dr. Andrew Sutherland, Cooperative Extension Advisor for Urban Integrated Pest Management in the San Francisco Bay Area, “The most effective strategy for prevention of mosquitoes and the diseases they transmit is to eliminate larval development sites: eliminate standing water by emptying or draining containers, filling flooded areas or containers that cannot be drained, properly maintaining gutters and downspouts, properly screening rain barrels and cisterns, and properly maintaining fountains and water gardens.” Sutherland also said that personal protection measures include wearing long pants and sleeves, using insect repellents recommended by the Centers for Disease Control and Prevention—such as DEET or picaridin—and avoiding times when mosquitoes are most active.
West Nile virus remains the most common mosquito-borne illness in California. In 2025 alone, at least 113 people were infected with West Nile virus in the state, resulting in 11 deaths. New invasive species like Aedes aegypti (yellow fever mosquito) have been detected recently in cities including San Jose, Livermore, and Antioch. These species breed in small amounts of water found around homes—such as buckets or bird baths—and can spread serious viral diseases.
University of California Agriculture and Natural Resources secures funding through public contributions to support its programs according to the official website. The organization promotes sustainable practices to strengthen resilient ecosystems and economic vitality according to the official website. It utilizes nine research and extension centers as laboratories representing California’s diverse ecosystems according to the official website.
The organization has gained recognition for its trusted services linking research to community needs according to the official website, is part of the University of California system managing Cooperative Extension services according to the official website, conducts over 33,800 educational events annually with more than 18,400 volunteers engaged according to the official website, and extends university research statewide through educational programs operating in all 58 counties according to the official website.
Looking ahead, UC Agriculture and Natural Resources encourages residents experiencing daytime “ankle-biter” mosquitoes or finding larvae in small containers at home to contact local vector control districts. The organization continues its outreach efforts through workshops and partnerships aimed at supporting environmental stewardship across California.