The Contra Costa Mosquito and Vector Control District announced that mosquitoes collected from a trap on Holland Tract this week tested positive for West Nile virus, marking the third group from that area to do so this year. Officials emphasized that these mosquitoes are not the same species that East Contra Costa County residents have been reporting. The infected mosquitoes are from the southeastern part of Holland Tract, while the mosquitoes that residents have noticed are coming from the northwestern part of the tract.
According to Scientific Programs Manager Steve Schutz, Ph.D., Contra Costa County is home to 23 native mosquito species, but only two, Culex tarsalis and Culex pipiens are efficient at transmitting West Nile virus. The mosquitoes residents have recently encountered, Aedes vexans, are aggressive biters but are not efficient at transmitting West Nile or other viruses. The District is currently working to locate and eliminate the sources of these aggressive mosquitoes in East County.
Because mosquitoes require water to develop, the District urges residents to dump out all standing water on their property at least once a week. If problems persist, residents are encouraged to request mosquito service from the District. To reduce the risk of mosquito bites, officials recommend using EPA-registered insect repellents that contain DEET, Picaridin, Oil of Lemon Eucalyptus (repellent form), or IR3535, and to always follow label instructions. Reporting dead birds is also critical, since they are often the first sign of West Nile virus in a community.
Residents can report dead birds or request mosquito service by calling (925) 685-9301 or visiting the District’s website.