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West Nile Virus Continues to Be Detected

Cotati, CA . October 6, 2023 – The Marin/Sonoma Mosquito and Vector Control District confirmed today that a sample of adult mosquitoes collected in a trap has tested positive for West Nile virus (WNV). This is the third mosquito sample to test positive for WNV in Sonoma County this year. The mosquito sample was collected from the vicinity of the Ellis Creek Water Recycling Facility in the City of Petaluma.

 “As residents enjoy the last warm days of the season, it is imperative that they employ personal protection measures when engaging in outdoor activities,” stated Nizza Sequeira, Public Information Officer. “Wearing long-sleeved shirts, long pants and applying insect repellent to exposed skin when outdoors can help reduce the risk of West Nile virus transmission.”  

District staff will continue to trap, test, and monitor the abundance of adult mosquitoes in the area where the positive mosquito sample was collected. In addition, vector control technicians are inspecting all documented sources of mosquito production, searching for new sources, and conducting mosquito control operations as necessary.  

Simple ways to reduce the risk of West Nile virus:

  • Use Mosquito Repellent: Apply an EPA-registered mosquito repellent on exposed skin containing one of these active ingredients: DEET, Picaridin, oil of lemon eucalyptus, or IR3535.
  • Wear Protective Clothing: Wear long-sleeved shirts and pants when outdoors, especially during dawn and dusk when mosquitoes are most active.
  • Eliminate Standing Water: Mosquitoes reproduce in standing water, so empty containers such as flower pots, bird baths, and ponds to reduce mosquito breeding sites.
  • Install Screens: Keep doors and windows screened to prevent mosquitoes from entering your home.
  • Report Mosquito Problems: Contact the Marin/Sonoma Mosquito & Vector Control District (707-285-2200) if you have a mosquito-related problem that you cannot resolve on your own.
  • Consult Your Veterinarian: Talk to your veterinarian about a West Nile Virus vaccination for your horses.

With West Nile virus being active in other parts of California, District officials recommend residents keep abreast of virus activity when traveling to other parts of the state. More information about West Nile virus in California can be found at

Visit for more information regarding mosquito and vector control.

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