West Nile is spreading faster than it has in 20 years. Here’s how to keep yourself safe

A growing number of deadly West Nile virus-carrying mosquitoes are spreading rapidly across Southern California and local officials are urging residents to take action to ward off a bite.

The virus is off to its earliest start in the United States in the last 20 years, federal officials warn, including in the Southland.

West Nile virus is the most common and serious mosquito-borne disease in California that can be fatal to humans and some wildlife, according to the California Department of Public Health.

In Los Angeles County, cases began to pop up in May, firstly in Pico Rivera and Long Beach, according to the Greater Los Angeles County Vector Control District. Now it’s up to 27 within its coverage area.

At the same time, more mosquitoes carrying the virus are being found.

“Within our service area, the five-year average for West Nile Virus-positive mosquito samples at this point in the season is approximately four,” said Caroline Gongora, public information coordinator for the vector control district. “This year, we have detected 38 positive 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, mosquitoes carrying West Nile have been found in 10 cities, with the latest being Fullerton and Anaheim.

Authorities find West Nile virus by capturing and testing mosquitoes in groups of 10 to 50 each, which they call a “mosquito pool.”

Last year, Orange County’s vector control detected West Nile virus in four mosquito pools. It detected it in five pools in 2024 and only one in 2023.

But this year, it’s found West Nile virus in 38 mosquito pools.

“We are 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 human disease cases nationwide, including 38 cases of severe neuroinvasive disease, a condition that results in the brain and surrounding tissues to becoming inflamed and could lead to permanent brain damage and even death, according to the Mayo Clinic. This is the highest number of human disease cases reported midway through the year since 2004, according to the Centers for Disease Control and Prevention.

There has only been one case of human infection in the state of California this year: a Long Beach resident who was hospitalized with neuroinvasive illness.

There is no specific treatment for West Nile virus. In more 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 out of 10 people who develop severe West Nile virus disease affecting the brain and nervous system die, according to the CDC.

Who is at risk of contracting West Nile virus and the resulting symptoms

Anyone is at risk of becoming infected with the virus; however, those at higher risk of developing serious illness and long-term health problems include people over 50 and those with preexisting health conditions.

A majority of people who become infected with the virus are asymptomatic.

About 20% of infected people will develop mild symptoms such as a fever, body aches and nausea. These symptoms usually start 3 to 14 days after being bit. Most mild symptoms get better on their own and last a few days.

In more severe cases, symptoms include high fever, headache, neck stiffness, vision loss, paralysis and coma. These more severe symptoms may last several weeks and lead to permanent damage to the brain and nervous system.

An estimated 1% will develop 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 result in an infection of the brain or surrounding tissue.

How to avoid a mosquito bite

The best way to prevent infection is to stop mosquitoes from breeding around your home and avoid getting bit.

You can help protect yourself by doing the following:

• Wear mosquito repellent directly on all exposed skin. The repellent should 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 during dawn and dusk.
• Avoid being outside between dusk and dawn, which is when the mosquitoes that spread West Nile virus are most active.
• Remove stagnant water around homes and eliminate containers that might catch and hold water.
• Empty or change water in pet bowls, bird baths and other outdoor containers at least once a week.
• Install or repair door and window screens.
• Support neighborhood mosquito control efforts by reporting neglected swimming pools, large mosquito breeding sites or unusually high mosquito activity to the Vector Control District.
• Report dead birds to the Vector Control District.

Greater Los Angeles County cities where West Nile virus-carrying mosquitoes were detected

• Pico Rivera
• Long Beach
• Cerritos
• Hawaiian Gardens
• Sunland
• Montebello
• Signal Hill
• Winnetka
• Atwater Village
• Boyle Heights
• East Los Angeles
• Paramount
• Northridge
• Valley Glen
• Carson
• Artesia
• Bellflower
• Downey
• Norwalk
• Rowland Heights
• Santa Fe Springs
• Whittier
• Woodland Hills
• Canoga Park
• Lakewood
• Porter Ranch
• Tarzana

Orange County cities where West Nile virus-carrying mosquitoes were detected

• Newport Beach
• Buena Park
• Costa Mesa
• Garden Grove
• Santa Ana
• Seal Beach
• Huntington Beach
• Cypress
• Fullerton
• Westminster