West Nile is spreading faster than it has in 20 years. Here's how to stay safe
A growing population of deadly West Nile virus mosquitoes is spreading rapidly across Southern California and local officials are urging residents to take action to prevent bites.
The virus first appeared in the United States 20 years ago, government officials warn, including in South America.
West Nile virus is the most common and dangerous mosquito-borne disease in California that can kill people and other wildlife, according to the California Department of Public Health.
In Los Angeles County, cases began appearing in May, first in Pico Rivera and Long Beach, according to the Greater Los Angeles County Vector Control District. It is now up to 27 in its coverage area.
At the same time, many infected mosquitoes are found.
“Within our facility, the five-year average of West Nile virus-infected mosquito samples this time of year is about four,” said Caroline Gongora, public information coordinator for the vector control district. “This year, we received 38 mosquito samples, a significant increase in activity compared to recent years.”
In Orange County, its vector control district reported its first disease-carrying mosquitoes in Newport Beach on June 2. Now, West Nile-carrying mosquitoes have been found in 10 cities, the latest being Fullerton and Anaheim.
Authorities detect West Nile virus by capturing and testing mosquitoes in groups of 10 to 50 people per group, which they call a “mosquito pool.”
Last year, Orange County vector control found West Nile virus in four mosquito pools. Found in five lakes in 2024 and only one in 2023.
But this year, West Nile virus was found in 38 mosquito pools.
“We're above average for this time of year,” said Miquel Jacobs, director of communications for the vector control district.
As of June 30, there have been at least 48 cases of human illness nationwide, including 38 cases of severe neuroinvasive disease, a condition that causes the brain and surrounding tissue to swell and can lead to permanent brain damage and even death, according to the Mayo Clinic. This is the highest number of human disease cases reported in a year since 2004, according to the Centers for Disease Control and Prevention.
There has been only one case of human infection in the state of California this year: a Long Beach resident who was hospitalized for neuroinvasive disease.
There is no specific treatment for West Nile virus. In severe cases, people may need to go to the hospital for supportive measures such as IV fluids, pain management and nursing care, according to the Centers for Disease Control and Prevention.
About 1 in 10 people who develop severe West Nile virus disease that affects the brain and nervous system die, according to the CDC.
Who is at risk of getting West Nile virus and the resulting symptoms
Anyone is at risk of contracting the virus; however, those most at risk of developing serious illness and long-term health problems include people over 50 and those with pre-existing health conditions.
The majority of people who become infected with the virus do not show symptoms.
About 20% of people infected with the virus will have mild symptoms such as fever, body aches and nausea. These symptoms usually begin 3 to 14 days after the bite. Most mild symptoms get better on their own and last a few days.
In severe cases, symptoms include high fever, headache, neck stiffness, vision loss, paralysis and coma. These more severe symptoms can last for several weeks and lead to permanent damage to the brain and nervous system.
It is estimated that 1% will have a neuroinvasive disease, according to the American Medical Assn. In these cases, the virus affects the brain or nervous system and can cause encephalitis or meningitis, which can lead to infection of the brain or surrounding tissues.
How to avoid mosquito bites
The best way to prevent infection is to prevent mosquitoes from breeding near your home and avoid being bitten.
You can help protect yourself by doing the following:
- Apply mosquito repellent directly to all exposed skin. The repellent must contain at least one of the following active ingredients: DEET, IR3535, oil of lemon eucalyptus or Picaridin/KBR 3023.
- Wear long-sleeved shirts and long pants outside in the morning and evening.
- Avoid being outside between dusk and dawn, which is when mosquitoes that spread West Nile virus are most active.
- Remove standing water around homes and remove containers that may catch and hold water.
- Empty or change the water in pet bowls, birdbaths and other outdoor containers at least once a week.
- Install or repair door and window screens.
- Support local mosquito control efforts by reporting neglected swimming pools, large mosquito breeding sites or unusually high mosquito infestations to the Animal Control District.
- Report dead birds to the Vector Control District.
Major cities in Los Angeles County where West Nile virus-carrying mosquitoes have been found
- Pico Rivera
- Long Beach
- Cerritos
- Gardens of Hawaii
- Sunland
- Montebello
- Signal Hill
- Winnetka
- Atwater Village
- Places to stay in Boyle Heights
- East Los Angeles
- Important
- Northridge
- Valley Glen
- Carson
- Artesia
- The Bellflower
- Downey
- Norwalk
- Residences in Rowland Heights
- Santa Fe Springs
- Whittier
- Residences in Woodland Hills
- Canoga Park
- Lakewood
- Porter Ranch
- Tarzana
Orange County cities where West Nile virus-carrying mosquitoes have been found
- Newport Beach
- Buena Park
- Costa Mesa
- Garden Grove
- Santa Ana
- Seal Beach
- Huntington Beach
- Cypress
- Fullerton
- Westminster
