San Joaquin County Mosquito and Vector Control District’s (District) vector-borne disease surveillance program recently detected the first mosquitoes positive for West Nile Virus (WNV) in San Joaquin County for 2026.
The sample of WNV-positive mosquitoes was collected from Upper Jones Tract in the San Joaquin Delta islands. This detection marks the beginning of WNV activity this season in San Joaquin County. The District laboratory collects and tests mosquitoes and dead birds for mosquito-borne diseases every week during the mosquito season, and WNV has been detected in the county every summer for more than 20 years.
The virus is maintained in nature through a cycle between wild birds and mosquitoes. As temperatures rise during the summer, mosquito populations increase, creating more opportunities for virus transmission. Most people infected with WNV do not develop symptoms, but some may experience mild to severe illness.
“As temperatures continue to rise this summer, residents should take steps to reduce mosquito development around their homes and protect themselves from mosquito bites,” said Sumiko De La Vega, Public Information Officer with the District. “We encourage residents to inspect their yards each week for standing water where mosquitoes can develop and to use EPA-registered mosquito repellents when outdoors.”
The District will continue to conduct mosquito surveillance and disease testing throughout the season.
The data collected allows the District to make informed, science-based decisions and focus control efforts in areas with elevated mosquito activity or disease risk.
Residents can reduce the risk of West Nile virus by taking the following precautions:
* Eliminate all sources of standing water on your property that can support mosquito development – even as little as a tablespoon.
* When outdoors, use an EPA-registered insect repellent according to label directions. Effective active ingredients include DEET, picaridin, IR3535, or oil of lemon eucalyptus: www.epa.gov/insect-repellents
* Avoid spending time outside when mosquitoes are most active, at dawn and dusk, especially for the first two hours after sunset.
* Wear loose-fitting clothing with long pants and long-sleeved shirts when outdoors.
* Exclude mosquitoes from your home with tight-fitting screens on doors and windows.
* Contact your veterinarian for information on vaccinating horses against WNV.
* For mosquito problems, request an inspection online on the District’s website: www.sjmosquito.org
* Report dead birds to 1-877-WNV-BIRD (1-877-968-2473) or to www.westnile.ca.gov.
To learn more about San Joaquin County Mosquito and Vector Control activities, visit the District’s website at www.sjmosquito.org.
