Eight more bird carcasses in Contra Costa County tested positive for West Nile virus, county authorities reported.
One was an American crow found in Walnut Creek on Tuesday, according to a chart on the website of the Contra Costa Mosquito and Vector Control District. Other birds were found in Concord, Clayton, Antioch, Brentwood, Discovery Bay and Oakley.
The local news came a day after national authorities took note of a sharp escalation in West Nile cases.
"The public is doing an excellent job of reporting dead birds to the state's dead bird hotline or reporting them online," said Deborah Bass, public affairs manager for the Contra Costa Mosquito and Vector Control District. "That helps us to understand where we need to target our mosquito control to protect everyone's health."
Some birds can be reservoirs for West Nile virus. Mosquitoes bite the birds and then can transmit the disease to people. Residents are urged to wear mosquito repellent when outdoors, especially at dawn and dusk when mosquitoes are present.
