The San Joaquin County Mosquito and Vector Control District’s laboratory surveillance and disease testing system has found West Nile Virus-positive mosquitoes for the last four consecutive weeks in the Tracy area. This past week, two positive mosquito samples were found in zip codes, 95376 and 95377. The first reported detection of West Nile Virus (WNV) was reported on June 20, 2025, in the same zip code, 95376. Since then, 11 out of 13 positive mosquito samples (84 percent) were in those zip codes. In addition, the week of June 29, the first positive dead bird, an American Crow from the Tracy area, tested positive for WNV.
“Detections of WNV in both birds and mosquitoes indicate there is active transmission occurring in the area,” explained Sumiko De La Vega, Assistant Entomologist with San Joaquin County Mosquito and Vector Control District.
“Rest assured that the District enhanced all resources available to reduce the risk of West Nile virus in the human population,” said Aaron Devencenzi, Public Information Officer with the District. “The District will continue to implement the California Mosquito-Borne Virus Surveillance and Response Plan to protect the public health and welfare.”
Recently, the District has made the following efforts to reduce the human risk of West Nile Virus:
Nineteen State Certified Mosquito Control Technicians check 150 to 300 known mosquito sources in their designated areas of operation every seven days and respond to service requests from the public.
The District will send a second “Notice” letter to suspect neglected swimming pool homeowners. Following the second letter will be a visit from a technician, and if necessary, followed by a warrant to inspect and treat neglected swimming pools. These dirty pools serve as a primary breeding ground for mosquitoes that vector WNV.
Over 80 surveillance traps are placed weekly to biweekly to assess the mosquito populations and test these samples for mosquito-borne diseases.
The District is spraying for adult and larval mosquitoes by ground and air in multiple areas where high populations of mosquitoes have been found or in areas of WNV concern.
People in San Joaquin County can receive spray notifications by signing up for the opt-in/opt-out email notification system, GovDelivery, at www.sjmosquito.org.
Public service announcements, via local newspapers, a local magazine, radio stations, and television stations, are in English and Spanish, and are active. For social media, the District’s website and Facebook (San Joaquin Mosquito & Vector) are also utilized.
The District strongly urges residents of San Joaquin County to remove all standing water around homes, as well as to be sure to reduce mosquito bites by using good screens on windows and doors. Officials also urge wearing an EPA-registered mosquito repellent like DEET when outdoors and encourage residents to talk to their neighbors regarding these recommendations.
Additional tips and information can be found at the San Joaquin County Mosquito & Vector Control website: www.sjmosquito. Statewide information on West Nile virus can be found at https://westnile.ca.gov/.
