West Nile virus-positive mosquitoes detected in San Jose

Caelyn Pender, The Mercury News on Aug 27, 2025

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SAN JOSE, Calif. — Mosquitoes carrying West Nile virus have been detected in the city for the first time this year, officials said.

The Santa Clara County Mosquito and Vector Control District will begin spraying treatments to control the population of adult mosquitoes that carry the virus, according to a press release. Officials did not immediately specify when or where the treatments would take place.

“Protecting our community from West Nile virus is one of our top priorities,” Dr. Nayer Zahiri, manager of the Mosquito and Vector Control District, said in a statement. “Our licensed technicians are in the field year-round, monitoring and treating areas where mosquitoes breed, helping to lower the risk of disease and keep Santa Clara County safe for everyone.”

The treatment will be conducted Aug. 29 beginning around 10 p.m. and last no more than four hours, said Carolyn Lê, senior communications officer for Santa Clara County’s Consumer and Environmental Protection Agency. It will encompass the zip codes 95118, 95124, 95125 and 95136. A map of the treatment area can be found online. Residents can search their address to see whether they are in the affected area.

The district anticipates that detections of West Nile-positive mosquitoes will increase, as mosquitoes thrive in the warm weather of the summer and early fall, officials said.

The treatments consist of pesticides that are approved by both state and federal environmental protection agencies, officials added. This treatment will use Zenivex, according to the county’s website.

West Nile virus can cause symptoms including tremors, paralysis, fever, muscle weakness, disorientation, joint pain, body aches, diarrhea, rash and vomiting, officials said. It is the most serious disease carried by mosquitoes in the county.

“Taking swift action is critical to protect public health,” Dr. Taylor Kelly, scientific technical services manager for the district, said in the press release. “Adult mosquito spraying treatments reduce the flying adult mosquito population in the area, which decreases the risk of a West Nile virus-human infection.”

West Nile virus can be serious for people who are over the age of 60 or those who have certain medical conditions, Dr. Sarah Rudman, acting health officer and director of the County of Santa Clara Public Health Department, said in the press release. Anyone experiencing symptoms should contact their health care provider.

“Unfortunately, there is no vaccine that prevents West Nile virus, so please take extra care to prevent these mosquitoes from spreading and making someone sick by removing standing water and using approved bug spray to avoid bites,” Rudman said.

The district asks that residents dump any standing water, including in pet bowls, flower pots and buckets. Any containers should be stored upside-down when not in use. Neglected or green swimming pools or fountains should also be reported to the county.

They also ask that residents sign up for mosquito treatment alerts.

Officials also encourage residents to report sightings of dead birds, which can be a sign of West Nile. Reports can be called into 877-WNV-BIRD or filed online at westnile.gov/report.

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