CONCORD, CALIFORNIA - The Contra Costa Mosquito and Vector Control District (District) is reporting one chicken from the District's sentinel chicken flock on Holland Tract, near Knightsen, and two chickens from a flock in Oakley have tested positive for antibodies against West Nile virus.
The District maintains flocks of sentinel chickens at four locations in Contra Costa County. District employees take a small blood sample from each chicken, specifically during the warmest months of the year when West Nile virus is most active. When a chicken is bitten by an infected mosquito, the chicken develops antibodies to fight off the virus. Samples that test positive for antibodies provide evidence of virus activity in specific areas of the county and help the District determine locations for prevention and control efforts.
In addition, one dead bird and one more group of trapped mosquitoes have tested positive for West Nile virus (WNV) in Contra Costa County. The dead bird was collected from Antioch, while the mosquitoes were trapped in Discovery Bay.
There have been 11 dead birds and eight groups of trapped mosquitoes that have tested positive for WNV so far in 2023. The District continues to advise all Contra Costa County residents to take the necessary steps to reduce the risk of mosquitoes and mosquito bites.