Placer County reports first human case of West Nile virus this season
PLACER COUNTY, Calif., September 23, 2026 – As West Nile cases statewide continue to soar, Placer County has recorded its first human case of this season – though the virus may have been contracted in another county. Regardless, with West Nile prevalent locally, the county’s health officer and the Placer Mosquito and Vector Control District encourage residents to reduce their risk of mosquito-borne illnesses. Since West Nile virus was first detected this season in June in Placer County, 9 dead birds and 112 mosquito samples have tested positive in the District.
Other counties in the region have already reported cases and deaths, and statewide case counts year-to-date are more than three times higher than they were at this point last year. West Nile virus is a potentially serious illness transmitted through the bite of a female mosquito, and there is no cure.
“West Nile virus continues to pose a real risk in our region, even for people who may feel perfectly healthy,” said Dr. Rob Oldham, the county’s health officer. “Most infections are mild, but serious illness can occur, which is why taking steps to avoid mosquito bites is essential.”
During high season, the District traps and tests mosquitoes for West Nile virus weekly throughout Placer County. These test results are used to assess the risk of virus transmission, inform the public, and guide preventative or responsive vector control treatments.
“As in previous years, our surveillance showed a peak in West Nile virus-positive mosquitoes in mid-summer, with activity typically decreasing as the weather cools,” said District General Manager Joel Buettner. “However, we expect other mosquito species that are not associated with West Nile virus transmission to remain abundant into the fall, and we urge residents to continue protecting themselves from bites by using repellent and wearing protective clothing.”
The risk for West Nile virus transmission to humans in Placer County remains high. The Mosquito and Vector Control District and the county’s Public Health division anticipate additional human cases as we move into fall. Officials recommend residents practice the “three Ds”:
- DUMP AND DRAIN – Mosquitoes lay their eggs on standing water. Eliminate all sources of standing water, including flowerpots, old tires, rain gutters, and pet bowls. If you know of a swimming pool that is not being properly maintained, contact the District at 916‑380‑5444.
- DEFEND – Apply an EPA‑approved insect repellent containing DEET, picaridin, oil of lemon eucalyptus, or IR3535 according to label instructions to defend yourself from bites. West Nile virus–transmitting mosquitoes typically bite in the early morning and evening, so proper clothing and repellent use during these times is important.
- DISTRICT – Contact the District for any additional help controlling mosquitoes around your home.
For more information about West Nile virus, visit California’s website at westnile.ca.gov. Residents are encouraged to report dead birds on the website or by calling toll‑free 1‑877‑WNV‑BIRD (968‑2473).
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Please direct all media inquiries to the District’s Public Information Officer, Emma Carlson, at pio@placermosquito.org.