The Contra Costa Mosquito and Vector Control District is trapping and testing mosquitoes for West Nile virus across the county, including the area it serves in Orinda, Moraga and Lafayette.
The agency's laboratory team was identifying mosquitoes and testing two species that can carry the virus as of Monday, Sept. 14, according to the District's social media posts. Seven birds and one group of mosquitoes had tested positive for West Nile virus in Contra Costa County as of Aug. 8, according to Contra Costa News. Four of the infected birds were found in El Cerrito, prompting the District to set traps there.
The local activity comes during a statewide spike. California recorded 126 human cases of West Nile virus in 2026 as of Saturday, Sept. 12, roughly triple the five-year average, with six deaths, Patch reported. Vector control officials statewide are expecting one of the worst years on record, based on thousands of mosquito samples testing positive in nearly every county.
One person in Contra Costa County died from West Nile virus in the past two years, according to state data cited by the Mercury News in August. The first Bay Area case of 2026 was confirmed in Santa Clara County.
No West Nile virus cases or positive mosquito samples have been publicly reported in Orinda, Moraga or Lafayette specifically. The nearest confirmed activity has been in El Cerrito and Martinez, where a mosquito sample tested positive in June.
"It is not a good year. Well, I guess it is a good year for mosquitos," Orange County Vector Control District spokesperson Brian Bannon told Patch on Saturday, Sept. 12, describing the statewide season. "Just not a good year for us, who don't really like them."
On Thursday, Sept. 10, the District said West Nile virus season is ongoing and urged residents to report dead birds to the California West Nile Virus Dead Bird Call Center. Dead birds are often the first sign of the virus in a given area, the agency said.
The District is also fighting a second threat: the invasive Aedes aegypti mosquito, known as the "ankle biter," which can breed in as little as a bottle cap's worth of standing water. The species has been detected in Antioch for three consecutive years and spread to multiple areas of Brentwood by Aug. 21.
To combat the Aedes aegypti in Antioch, the District launched a pilot program on July 7 that releases Wolbachia-infected male mosquitoes weekly through October. When these males mate with wild females, the resulting eggs do not hatch. The method targets only Aedes aegypti and leaves other insects unharmed, according to the District's website.
Lamorinda residents have direct representation on the District's Board of Trustees. Kevin Marker serves as board president representing Orinda, Derrick Seaver represents Lafayette and James Frankenfield represents Moraga, according to the board's July 13 meeting minutes.
The District is funded by property taxes and benefit assessments, so there is no additional charge when residents request service. Residents can reach the agency at (925) 685-9301 or visit the District's website to report mosquito problems or view the 2026 West Nile Virus Activity map.
