VISALIA, CA – The General Manager of Delta Mosquito and Vector Control District, Dr. Mustapha Debboun, confirmed today that 7 mosquito samples have tested positive for West Nile virus (WNV). These are the first WNV positive mosquito samples of the season. The warm weather from the previous week increased the number of mosquitoes and virus activity for the region. “Every summer, WNV activity picks up with warming weather and mosquito activity in the District and across California” said Dr. Mustapha Debboun. “Other nearby counties have already reported increased virus activity,” added Dr. Debboun.

Culex mosquito blood feeding

The native mosquito Culex quinquefasciatus takes a blood meal. West Nile Virus is transmitted to people through the bite of an infected mosquito. Photo credit: CDC PHIL James Gathany

WNV is transmitted through the bite of an infected mosquito. Mosquitoes become infected after feeding on an infected bird. WNV is typically transmitted by Culex mosquitoes. “Culex mosquitoes prefer to feed on birds and are active around dusk and dawn,” said Dr. Mustapha Debboun. He added “The first line of defense against mosquito bites is to use an environmental protection agency (EPA) registered insect repellent.”

According to the California Department of Public Health website, EPA-registered repellents “are safe to use and work best to protect against mosquito and tick bites when used according to label directions.” The active ingredient in EPA-registered insect repellents have been evaluated for human safety and effectiveness. EPA-registered repellents contain one of the following active ingredients:

  • DEET
  • Picaridin
  • IR3535
  • Oil of Lemon Eucalyptus (OLE)
  • Para-menthane-diol (PMD)
  • 2-Undecanone

Residents who would like help finding an appropriate repellent can use the EPA’s online repellent tool at

Reducing the mosquito population can also help reduce the mosquito-borne disease risk. Mosquitoes lay their eggs on standing water and can develop from an egg to a biting adult in as little as 5 to 7 days. Neglected pools and hot tubs, a common source of standing water for Culex mosquitoes, can produce millions of adults.

District residents are encouraged to report neglected swimming pools, dead birds, and other mosquito problems to Delta Mosquito and Vector Control District at 559-732-8606 or online at

June 8, 2021 Press Release