California's West Nile surge has killed 32 people, and experts are 'scared of next year'

Mosquito-control experts are concerned about another difficult season ahead as California confronts a surge in West Nile virus, and the California Department of Public Health reports that the virus has killed 32 people.

California had not seen this much West Nile activity in five years, but warm, rainy summer and fall weather helped drive the increase, CalMatters reported.

Here's what to know

Los Angeles County accounted for more than half of California's reported human cases. 

Statewide, 528 people had become seriously ill from the virus as of Nov. 6, according to California Department of Public Health figures cited by CalMatters.

About one in 150 people infected with West Nile develops a serious illness, which can involve brain inflammation, neurological problems, or death. Roughly 20% experience fever, headache, and body aches, though most infected people never feel sick.

Supportive care is the only medical treatment available.

The prospect of heavy rain has officials concerned about what lies ahead. Lower nighttime temperatures can slow the virus's growth and reduce mosquito reproduction.

Paula Macedo, chair of the Mosquito and Vector Control Association of California, admitted that this year's surge in cases, coupled with long-range forecasts, has worried public health officials.  

"With the amount of activity that we already saw this year and having the forecast of being an El Niño year, we are all bracing ourselves," she said.

More background

Temperatures reached 104 degrees after September rainfall associated with Hurricane Marie, and overnight lows stayed above 77. 

The rain also washed mosquito-control treatments out of an underground drainage network spanning more than 3,000 miles, according to the Greater Los Angeles County Vector Control District.

A UC Berkeley study examined data collected around Los Angeles between 2006 and 2016 and found that West Nile became much more likely to appear in mosquitoes when average temperatures exceeded about 73 degrees.

Coastal Los Angeles' summer averages sit near that threshold. Flooding revived Tulare Lake in 2023, creating mosquito habitat. California recorded 433 human cases that year.

Drought can also coincide with severe outbreaks. During the severe drought years of 2014 and 2015, West Nile infected upwards of 1,600 people.

What can be done?

The California Department of Public Health and vector-control experts recommend emptying standing water weekly, including water found in plant saucers, pet dishes, toys, and birdbaths.

Permanent ponds can be treated with larvicides, and some districts supply mosquitofish to help control mosquito populations.

Residents can also protect themselves by using repellent containing EPA-registered ingredients, including oil of lemon eucalyptus, DEET, or picaridin. 

Wearing long sleeves and pants outdoors between dusk and dawn is another precaution, since West Nile-carrying Culex mosquitoes bite during those hours.

People experiencing confusion, muscle weakness, a severe headache, or a stiff neck should seek medical care, especially those over 60. Residents can also report dead birds, with particular attention to California Scrub-Jays, ravens, and crows, at westnile.ca.gov/report.

California districts spend millions annually on mosquito trapping and extermination. Meanwhile, the Centers for Disease Control and Prevention is exploring better diagnostic tests, treatments, and vaccine development.

Unpredictable outbreaks, however, make the large clinical studies needed for a vaccine difficult to conduct.

Macedo said residents can help mosquito control crews identify and reduce breeding sites around their homes.

"We cannot enter every property. We cannot treat every mosquito source," she explained. "We need people to understand how they can prevent the situation."

Where can I learn more?

Other states are also dealing with mosquito-borne illnesses and concerns about where mosquitoes breed.

• New York has already recorded more West Nile cases in 2026 than in all of 2025.

• In Maryland, residents said overwhelming mosquito swarms made stepping outside impossible for three weeks.

• San Antonio neighbors called a clogged stormwater basin a mosquito factory as water lingered.

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