Contra Costa Combats West Nile Virus In Area Of High Detection

CONTRA COSTA COUNTY, CA— The Contra Costa Mosquito and Vector Control District was expected to use truck-mounted equipment Monday night to control adult mosquitoes in Oakley following a high number of mosquitoes and the detection of West Nile virus in the area.

An East Contra Costa man died last month from West Nile virus infection — the first West Nile virus-related death reported in the county since 2006.

Last week, two groups of mosquitoes trapped in Oakley tested positive for West Nile virus (WNV). In addition to the mosquitoes, four dead birds tested positive for WNV, and five sentinel chickens tested positive for antibodies. WNV-infected dead birds have also been reported this year from Alameda, San Mateo and Santa Clara counties; while Alameda, Santa Clara and Solano counties have also confirmed they found WNV-infected mosquitoes this season.

The spraying of a public health pesticide called Zenivex E4 RTU was set to take place between dusk —approximately 8:30 p.m. —and 11 p.m., weather permitting in an area of Oakley bordered on the north by Big Break/ SanJoaquin River; on the south by railroad tracks; on the east by Fetzer Lane; and on the west by Piper Lane above Rutherford Lane.

The majority of the district's mosquito control is completed when mosquitoes are still in their aquatic form, in their water source. Once mosquitoes emerge from the water as adults, the only effective method to control them is adult mosquito control. According to Paula Macedo, the district's general manager, the district uses products registered with the Environmental Protection Agency (EPA) and California Department of Pesticide Regulation (DPR), and the products are applied by trained and certified technicians according to label instructions.

So far this year in California, there have been nine human cases of WNV reported from six counties. Contra Costa County reported the state's lone fatality in 2024.

About one in five people who become infected with West Nile virus will have symptoms like fever, headache, body aches, nausea and vomiting in the days after being bitten by a mosquito. Just one bite can spread WNV, but people can protect themselves with an EPA-registered mosquito repellent.

To reduce the risk of mosquitoes on residential properties, the district recommends Contra Costa County residents look around their front and backyards at least once a week and dump out any amount of standing water. Also, check window screens to make sure they fit properly without any gaps or rips in the screen.

Contra Costa County residents can report dead birds online or by phone at 877-WNV-BIRD (968-2473). To request mosquito service for residential property, go online or call 925-685-9301.