West Nile virus showed up in Shasta County mosquitoes for the first time in 2025, according to Shasta Mosquito and Vector Control District, putting people at risk of being bitten and catching the disease.
A batch of the biting bugs captured by the agency in northeastern Redding tested positive for West Nile on Thursday, July 10, said Vector District Manager Darcy Little. That prompted the district to ramp up efforts to slow mosquitoes spreading the disease, stopping them where they often live.
Mosquitoes that carry the West Nile virus and other diseases thrive in wet environments (ponds, bird bathes, outdoor pet dishes, etc.) in places where temperatures soar into triple digits, like Redding and Anderson. However, they can show up in all parts of Shasta County, Little said.
Over the past two years, the first mosquitoes carrying West Nile that season were trapped in Shingletown and Burney. The single case of West Nile found in a human in 2024 came from the Burney Basin, too, according to Little, but there have so far been no human cases in Shasta County in 2025.
The mosquito-borne virus ― which causes disease in humans, birds and horses ― can make people very sick, in rare situations killing those infected. When humans get West Nile, they almost always contract it from the bite of an infected mosquito, not through contact with people or other animals with the disease, according to the district.
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What Shasta County is doing to slow West Nile from spreading
Finding West Nile in mosquitoes spurred district efforts to trap young mosquitoes throughout the county and test them for West Nile.
The district also conducted the first of three “ultra-low volume adult mosquito control” sprays on Friday morning in Redding where the disease-carrying insects were found. The spray used is a “fine mist that only affects soft-bodied insects such as mosquitoes.” That mist and the district’s other mosquito control products quickly biodegrade, according to Little.
People can sign up for alerts or track control efforts on the agency’s web page at shastamosquito.org.
Where West Nile virus showed up in California so far this season
As of Friday, Shasta County is the only California county north of Yuba and the Sacramento area to report finding West Nile in its borders in 2025.
Statewide, 21 counties tracked mosquitoes and/or birds that tested positive for West Nile Virus this year, according to the California Department of Public Health. Of those counties, only Stanislaus and Tulare each reported one human case of West Nile.
What are symptoms of West Nile
Most people who get West Nile don’t show symptoms, but about 20% get a fever with some combination of headaches, joint or other body aches, vomiting, diarrhea or rashes. “Most people… recover completely, but fatigue and weakness can last for weeks or months,” according to the U.S. Centers for Disease Control and Prevention.
West Nile can cause severe illness in roughly one in 150 people, sometimes killing the person. The disease can cause problems with the central nervous system, including inflammation in or around the brain and/or spinal cord, the CDC said.
How to help protect people and animals from West Nile virus
Vector control recommends people help prevent the virus by preventing mosquito bites using the four Ds:
Jessica Skropanic is a features reporter for the Record Searchlight/USA Today Network. She covers science, arts, social issues and news stories. Follow her on Twitter @RS_JSkropanic and on Facebook. Join Jessica on Record Searchlight Facebook groups Get Out! Nor Cal , Today in Shasta County and Shaping Redding’s Future. To support and sustain this work, please subscribe today. Thank you.
This article originally appeared on Redding Record Searchlight: Shasta County mosquitoes test positive for West Nile virus for first time in 2025
Reporting by Jessica Skropanic, Redding Record Searchlight / Redding Record Searchlight
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