A group of mosquitoes in Contra Costa County tested positive for West Nile virus, the first signal of the virus in the county this year, officials said Friday.
The mosquitoes were caught in a trap near Byron, about 30 miles away from where a dead bird tested positive for West Nile last week, just across the Alameda County border, in Dublin.
August and September are peak season for mosquito-to-human transmission of the West Nile virus, said Steve Schutz, the Contra Costa Mosquito and Vector Control District’s scientific programs manager.
Already, there have been cases detected in Contra Costa, Alameda and Santa Clara counties this August. Further east, there have been dozens of cases detected around Stockton, Modesto and Sacramento. Around the state, cases have been found in 27 counties so far this year, according to the California Department of Public Health.
District officials are asking residents to take preventative measures such as draining any standing water on their property, properly treating their pools and using repellent while outside, especially during the peak dawn and dusk hours.
West Nile is most commonly spread to humans through the bite of a mosquito, though human infection is rare, and severe symptoms even rarer. About one in five people who are infected with West Nile will develop a fever and other symptoms, according to the Centers for Disease Control and Prevention, while it can prove fatal for about one of every 150 infections.
There have been 66 cases of West Nile in humans in Contra Costa County since 2005, including two people who died in 2006, according to the agency.
There have been 18 people to test positive for West Nile in California this year, the bulk of them in Los Angeles and Stanislaus counties. Typically between 200 and 800 people are infected each year in California, according to tracking done by the state health department.
Birds are one of the most common vectors of the mosquito-borne disease, and dead birds, particularly jays and crows, can be a sign of its spread in an area, Schutz said.
The county is asking residents to report dead birds to the state’s West Nile Virus Hotline online or by phone at (877) WNV-BIRD (968-2473).
