San Diego West Nile Virus Cases Hit 10-Year High as County Deploys Mosquito Spraying Trucks, Officials Warn

SAN DIEGO — San Diego County health officials are urging residents to take precautions against mosquito bites after West Nile virus cases surged to their highest level in a decade, prompting emergency spraying operations in neighborhoods identified as having elevated risk.

The county has confirmed 11 cases of West Nile virus so far this year, a stark increase from last year, when no cases were reported in the county at all. Of those 11 confirmed cases, four people have required hospitalization.

In response to the surge, county vector control officials deployed spraying trucks early Friday morning in Coronado, an area identified as having a particularly high concentration of cases, with plans to return Saturday at 1 a.m. to spray again. Signs alerting residents to the spraying operation have been posted throughout the affected neighborhoods, with a map outlining the treatment area spanning from 2nd Street to Ocean Boulevard and from F Avenue to Glorietta Boulevard.

Vector control officials explained the basis for targeting that specific area. “Identified an area that we see as having a higher risk of West Nile virus, based on finding positive mosquitoes within a limited area,” officials said.

West Nile virus typically originates in infected birds, which mosquitoes then pick up and transmit to humans through bites. According to health officials, approximately 80% of people who become infected with the virus do not develop any symptoms at all. Among the remaining 20% who do become symptomatic, most experience flu-like symptoms, including fever and muscle aches. Severe symptoms occur in roughly 1% of cases, and in some of those instances, the virus can prove fatal.

San Diego County Public Health Officer Dr. Sayone Thihalolipavan emphasized the importance of prevention given the current lack of medical treatment options for the virus. “It’s really important to understand there is no vaccine, there is no treatment for West Nile virus, so we have to take prevention really, really seriously,” Thihalolipavan said.

With no vaccine or specific treatment available, county officials are focusing their public messaging on practical prevention steps residents can take at home. Officials are advising residents to eliminate any standing water around their properties, including in flower pots and bird baths, since stagnant water provides breeding grounds for mosquitoes. Additional recommended precautions include using insect repellent and wearing long sleeves and pants when outdoors, particularly during dawn and dusk hours, when mosquito activity typically peaks and residents face the greatest risk of exposure.

Officials also flagged a broader environmental factor that could extend the current elevated risk beyond the season’s typical peak. A forecasted El Niño weather pattern may generate additional standing water across the region, potentially prolonging mosquito breeding conditions beyond West Nile virus’s typical peak season, which generally runs from June through October in the county.

The surge in San Diego County cases mirrors a broader national trend this year. According to the Centers for Disease Control and Prevention, an unusually warm and wet spring contributed to an early surge in mosquito breeding and virus circulation across the United States this year, a pattern that appears to be reflected in San Diego County’s own significant year-over-year increase in confirmed cases.

West Nile virus has circulated in the United States for more than two decades since it was first detected domestically, with case counts fluctuating from year to year depending on weather conditions, mosquito population levels and other environmental factors that influence transmission. The jump from zero confirmed cases in San Diego County last year to 11 this year, with four requiring hospitalization, represents a particularly sharp swing that has prompted the county’s more aggressive spraying response in the areas identified as highest risk.

Residents in Coronado and surrounding areas covered by the current spraying operation are advised to review the posted notices and treatment area maps for specific guidance on the timing and scope of the mosquito control efforts in their neighborhoods. County officials have indicated they will continue monitoring mosquito populations and case counts closely, with additional spraying operations possible in other areas of the county should further zones of elevated risk be identified through ongoing mosquito surveillance testing.

With the current case count already the highest recorded in the county in ten years and the season’s typical peak transmission window still ongoing, county health officials are continuing to emphasize that individual prevention measures, eliminating standing water, using repellent, and covering exposed skin during peak mosquito activity hours, remain the most effective tools available to residents in the absence of any vaccine or specific medical treatment for the virus.