Los Angeles County has recorded 100 cases of mosquito-borne West Nile virus, marking the highest total reported there in nearly a decade.
Of those cases, 90 involved neuroinvasive disease, meaning the virus crossed the blood-brain barrier and reached the meninges, the membranes surrounding the brain and spinal cord. Such infections can cause meningitis and, in some cases, paralysis.
The 90 neuroinvasive cases include 70 cases of encephalitis, or brain inflammation; 12 cases of meningitis; and eight cases of acute flaccid paralysis.
Ninety-four people have been hospitalized, while five have died from the virus.
The figures represent a sharp rise from last year, when Los Angeles County reported 22 West Nile virus cases, including 17 neuroinvasive infections. Two people died from the disease in 2025.
The county last reported at least 100 cases in 2017. That year, health officials recorded 268 cases over the full mosquito season.
Los Angeles County Health Officer Dr. Muntu Davis said the number of severe infections and deaths was concerning, warning that the region remains in the peak period for West Nile virus transmission. “It is important that everyone take steps now to protect themselves and their families,” he said.
Jason Farned, manager of the San Gabriel Valley Mosquito and Vector Control District, said West Nile activity was higher than usual. He added that teams were carrying out enhanced surveillance, targeted mosquito-control treatments, disease investigations and expanded community outreach and education.
West Nile is fatal for about one in 10 people who develop nervous system infections, or roughly one in 1,500 people infected with the virus.
Mosquito-borne illnesses, along with mosquitoes carrying dangerous pathogens such as West Nile virus and dengue fever, are spreading across the United States in greater numbers and appearing in new areas.
Warmer temperatures, rapid urban growth and international travel are helping mosquitoes and the diseases they carry expand into areas where they were previously uncommon or absent.
Most people infected with West Nile virus develop no symptoms or only mild illness. However, some can suffer life-threatening brain inflammation, other nervous system infections and paralysis.
The virus is transmitted through bites from Culex mosquitoes. It is most common in Great Plains states, including North Dakota, South Dakota, Nebraska and Colorado, although heavily populated metropolitan areas such as Los Angeles, Chicago and Dallas-Fort Worth also report high case numbers.
In many of these states, the mosquito season—which generally runs from late spring through early fall—has lasted longer as mosquito numbers have increased later in the year.
West Nile virus typically causes no symptoms. About one in five infected people develop symptoms such as fever, headache, nausea, diarrhea, joint pain and pain behind the eyes.
Approximately one in 150 infections becomes neuroinvasive, meaning the virus crosses the blood-brain barrier and reaches the meninges, potentially causing meningitis and paralysis.
West Nile is fatal for about one in 10 people who develop nervous system infections, equivalent to roughly one in 1,500 people who contract the virus.
According to CDC data, which generally trails state and local reporting, the United States has recorded 813 West Nile virus cases, including 607 cases of neuroinvasive disease.
Cases have been reported in 43 states.
There were 2,167 West Nile virus cases nationwide last year.
It’s unclear how many of last year’s cases were neuroinvasive, but CDC data shows there were 1,342 hospitalizations for neuroinvasive disease.
There were 172 deaths recorded last year.
Older adults, people with weakened immune systems and those with certain chronic conditions face the highest risk of severe illness due to West Nile.
Survivors of severe West Nile illness may experience long-lasting complications, including memory problems, chronic fatigue, muscle tremors or permanent neurological damage.
West Nile virus can be prevented primarily by avoiding mosquito bites.
CDC officials recommend using insect repellents that contain the ingredient DEET, wearing long sleeves and pants outside and staying inside between dusk and dawn during the summer.
