BRENTWOOD, Calif. (KRON) – Two more groups of mosquitoes tested positive for West Nile Virus, according to the Contra Costa Mosquito and Vector Control District.

Both groups were collected in eastern Contra Costa County: Holland Tract and an agriculture area near Brentwood.

There are now seven groups of mosquitoes and a dead bird that have tested positive for the virus in Contra Costa County this year.

“Mosquitoes develop from egg to biting adult in water, even small amounts of water. That’s why it is very important for Contra Costa County residents to dump out any amount of water that collected in buckets, toys, tools, and any other outdoor containers during the recent rain. Even an amount as small as a bottle cap full of water can produce mosquitoes. And it is especially important to reduce the risk of mosquitoes in late summer and early fall because this is the time of year when we typically see the largest number of human cases of WNV. The risk of WNV does not truly diminish until nights become chilly,” said Steve Schutz, Ph.D., Scientific Program Manager.

How the virus is transmitted:

  • Some birds carry the virus
  • A mosquito bites and infected bird which can infect the mosquito
  • Infected mosquitos then spread the virus by biting another bird or a person

Officials recommend reporting dead birds as this can be the first sign of the virus.

Residents are advised to dump out any standing water to reduce the risk of mosquitoes.

Residents in the county can also request mosquito service for their property by calling (925) 685-9301.

To report a dead bird, call (877) 968-2473.