CONCORD, CALIFORNIA - The Contra Costa Mosquito and Vector Control District (District) reports the third dead bird and third group of trapped mosquitoes have tested positive for West Nile virus (WNV) so far this year in Contra Costa County. The dead bird is a California scrub jay, collected from Oakley, and the mosquitoes were trapped in Brentwood.

The dead bird and mosquitoes are the latest evidence of WNV this year in Contra Costa County. Last month two groups of trapped mosquitoes from Discovery Bay and two dead birds; one from Brentwood and the other from Martinez, also tested positive for WNV in 2023.

WNV can be transmitted to birds, other animals, and people through a single mosquito bite. With WNV activity on the rise within Contra Costa County, the District recommends county residents take steps to avoid mosquito bites and reduce the risk of WNV.

"Statistically, this is the time of year when we typically see the highest risk of human cases, so it is very important for Contra Costa County residents who plan to be outside when mosquitoes are present, to wear an EPA-registered insect repellent that includes one of the four most effective active ingredients: DEET, Picaridin, IR3535, or the repellent version of Oil of Lemon Eucalyptus. And always follow the instructions on the label when using insect repellent," said Steve Schutz, Ph.D., Scientific Program Manager.

At times when mosquito repellent is unavailable, wearing long sleeves and long pants can reduce the amount of exposed skin that could be bitten by a mosquito.

In response to the increase in WNV activity, District employees will be conducting surveillance and control as needed in the areas where the dead bird and mosquitoes were found. At the same time, the District urges county residents to take the following steps around their homes to reduce the risk of mosquito bites and mosquito production:

  • Dump out standing water and scrub the inside of the container to remove mosquito eggs
  • Make sure door and window screens are in good working condition
  • Contact the District to request mosquito service

Contra Costa County residents can report dead birds by phone at (877) WNV-BIRD (968-2473) or online. County residents can also request mosquito service for their residential properties by calling (925) 685-9301 or online.

Since 2005, 75 people in Contra Costa County have been diagnosed with West Nile virus. In 2006, two people died from the disease. For human case information, please visit the California Department of Public Health Vector-Borne Disease Section online.
Contra Costa Mosquito & Vector Control District, an independent special district and public health agency, is located at 155 Mason Circle in Concord.