An especially pernicious mosquito season is presenting an added threat to humans, as county health officials report 18 human transmissions of West Nile virus, including two infections in Huntington Beach and one in Costa Mesa. And that’s just months into a season that could continue to intensify as a significant El Niño weather pattern stokes high surf conditions and creates warm, humid conditions favored by the cold-blooded biting insects.
Positive mosquito samples found in early June by the Orange County Mosquito and Vector Control District predicted an early and intense virus season, county health officials warned online this summer. So far that forecast is turning out to be true. As of Tuesday, the agency had identified 747 positive mosquito samples countywide — more than four times the 186 collected throughout all of 2025.
The same upward trend can be seen in human cases, with only four infections logged last year. “This is definitely one of the worst years we’ve seen, and we’re not far along into it,” OCMVCD spokesman Brian Brannon said Friday. “With West Nile virus, people typically only report it when they get really sick. So if we have 18 people who’ve come forward, there are certainly more out there.” It’s unclear exactly when and where the infections in Costa Mesa and Huntington Beach occurred, as Orange County Health Care Agency officials Friday would not speak on cases involving patients.
Brannon said his agency is spraying affected areas
Brannon said his agency is spraying affected areas with the larvicide BTI (Bacillus thuringiensis israelensis) which kills developing mosquitoes before they reproduce. Available commercially, the substance is generally safe for humans, pets and pollinators, he added. Hitting city streets after midnight, a residential truck-mounted treatment program sprays areas identified as having a lot of mosquito activity with ultra-low-volume adulticide to keep mature insects from repopulating.
Information on the agency’s website shows nighttime spraying occurred along Costa Mesa’s Harbor Boulevard, between Adams Avenue and Wilson Street, from midnight to 5 a.m. Wednesday through Friday. Larvicide applications have also been performed near Huntington Beach’s Bolsa Chica Wetlands. Orange County’s first human West Nile virus case was reported Aug. 5 in Anaheim, which has since logged four more infections.
Garden Grove, Fullerton and Cypress each have two recorded cases, while the cities of Seal Beach, Westminster and La Habra have one reported incident apiece. Another human case has not been linked to a geographic area, according to an online map maintained by OCMVCD. Officials advise residents to wear mosquito repellent containing DEET and loose-fitting clothing at dawn and dusk, as there is no known vaccine for the virus and no specialized medical treatments once someone becomes infected.
Most people with the virus show no symptoms,
Most people with the virus show no symptoms, but some may develop mild illness marked by fever, nausea and body aches or more grave symptoms deputy medical director of Communicable Disease and Control for the Orange County Health Care Agency. “More severe disease involves infection of the brain and the lining of the brain,” Zimmerman said by email Friday
“In such cases there can be loss of consciousness, stroke-like symptoms, and, in the worst circumstances, [infection] can lead to death.” Signs posted in public may indicate the virus has been detected nearby. Anyone seeking assistance with mosquito abatement is asked to call OCMVCD’s main line at (714) 971-2421 or visit ocvector.org.
