Two dead birds found in Discovery Bay have tested positive for West Nile virus, according to the Contra Costa Mosquito & Vector Control District.
In addition, mosquitoes found in Oakley and Discovery Bay also tested positive, the district said Friday in a news release.
There have been a total three dead birds and five groups of mosquitoes so far this year to test positive for the virus in Contra Costa County, according to the district.
"West Nile virus activity typically peaks in August and September, when baby birds have left their nests and mosquitoes begin to feed on humans more often," Steve Schutz, the district's scientific programs manager, said in a statement.
Last month, the district's sentinel chicken flock in Martinez tested positive, the first sign of West Nile virus activity in the central part of Contra Costa County.
Since 2005, 63 Contra Costa residents have been diagnosed with West Nile virus, according to the district. In 2006, two people died from the disease.
Mosquitoes that can transmit West Nile virus are active at dawn and dusk. To avoid bites, residents should stay indoors in the evening and wear mosquito repellant while outside. Repellants with DEET, picardin, oil of lemon eucalyptus are recommended by the Centers for Disease Control.
To reduce the risk of West Nile or other mosquito-borne diseases, residents should dump or drain standing water, according to the district.
Dead birds should be reported to the state West Nile hotline, at (877) 968-2473.