slideshow

The Contra Costa Mosquito & Vector Control District will fog for mosquitos carrying the West Nile Virus in Brentwood Thursday after two groups of mosquitos from there tested positive for the virus.

The district also announced that three chickens from Holland Tract west of Oakley tested positive for West Nile, as did four  birds in Brentwood, and one bird each from Antioch, Pleasant Hill and Walnut Creek.

Fogging for adult mosquitos will begin at dusk on Thursday, Aug. 23. The area being fogged is from Brentwood Boulevard east to Sellers Avenue, and from Elkins Way near Sunset Park on the north to approximately the ECCID canal near the Brentwood Police station on the south.

"Once we determine there is a risk to people, we act immediately to protect their health," District Operations Manager Carlos Sanabria said Wednesday.

Sanabria said the infected chickens are from one of a half-dozen flocks the district maintains to track mosquito-borne viruses, and the discovery of West Nile among them is significant.

"That's huge," he said. "When chickens start getting it, people often start getting it at the same time."

Since 2005, 39 people in Contra Costa County have been diagnosed with West Nile virus. In 2006, two people died from the disease. About one in 150 people infected with West Nile virus will develop severe illness.

The source of the mosquitos in Brentwood is difficult to pin down because the mosquitos that tested positive are associated with backyard sources, Sanabria said. Previous positive tests were mostly associated with underground water sources.

Sanabria said particular attention has been paid to a storm retention basin at Heron Park, though it is not believed to be the source of the mosquitos. The basin has been heavily treated, he said, and the mosquitos trapped there have been mostly females with a longer flight range. Male mosquitos tend to stay near where they are born, and few males have been captured at Heron Park.

Sanabria said it was important for residents to walk around their home and empty any standing water to prevent mosquito breeding. The area being sprayed Thursday is slightly larger than that sprayed about two weeks ago, and district workers have scoured the area for breeding grounds.

"We've done just about everything we can think of, but we're still finding them,"Sanabria said.

Residents are also encouraged to wear mosquito repellant when outdoors, especially at dawn and dusk, when mosquitos are present.

Thursday's spraying will be done by truck between 8 and 11 p.m. If infected mosquitos persist, Sanabria said, additional fogging could be done next week.

For the full news release, including information on further protecting yourself from West Nile Virus, click here.