Mosquitoes,West Nile virus activity looks increasingly bad this year in OC

Orange County is “well on its way” to having the largest number of West Nile virus-carrying mosquitoes in the county’s history this season, local officials warn.

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West Nile virus is the most common mosquito-spread illness in the United States. Mosquitoes carry the virus after biting infected birds. And they can pass it to humans, potentially causing illness, through their bites.

Authorities detect the virus by capturing and testing groups or “mosquito pools” of 10 to 50 of the insects at a time.

“At the end of 2025, we had 186 mosquito pools that tested positive for West-Nile. Right now, this year we have 102 total positive mosquito pools,” said Brian Brannon, a spokesperson with the Orange County Mosquito Vector and Control District.

“And I am hearing that we’re going to see a lot more next Monday,” he said. “So we are well on our way to having the most heavy amount of West Nile virus activity in the history of Orange County and the Mosquito Vector and Control District.”

Most people who become infected with the virus won’t experience symptoms.

But one in five people may experience mild, flu-like symptoms, such as fever, headache, body aches or rash, according to the Centers for Disease Control and Prevention.

In rare, severe cases, contracting the virus can lead to a central nervous system infection and cause inflammation in the brain and the membranes surrounding the brain and spinal cord, resulting in hospitalization or even death.

About 2,000 people annually are officially diagnosed with West Nile virus in the U.S. — the number could be higher because people could attribute symptoms to other causes.

One in 10 people who contract West Nile and develop severe illnesses affecting the central nervous system die, according to the CDC.

OC Vector Control first reported West Nile-positive mosquito samples this year in Newport Beach on June 2.

As of Friday, July 24, the district had found West Nile in 16 Orange County cities, with the heaviest numbers being recorded in the northwest part of the county, in Anaheim, Buena Park and Fullerton.

“Last year, we had four human infections with West Nile virus in Orange County,” Brannon said. “We haven’t had any human infections this year. And our goal was to be proactive and to respond as quickly and as efficiently as possible when we detect the presence of disease.”

“So that’s what we’re gonna do.”

What’s being done?

Hotter weather means faster breeding for mosquitoes, which means, naturally, more carrying West Nile, Brannon said.

“We had an unseasonably warm year from the get-go here,” he said, “and mosquitoes are warm-blooded animals, so when it gets warmer, they’re more active.”

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The mosquito district is doing a few things to curb the uptick.

“We have a team that drives around in right-hand driving Jeeps so that they can drive along curbs in neighborhoods where the water and gutter backs up,” Brannon said.

“So they’ll go, and they have a little spray gun, and they put some mineral oil on that standing water and the gutters that will prevent the larvae from being able to breathe,” Brannon said.

The Vector Control District, starting in May each year, also sterilizes and releases up to 100,000 male mosquitoes in Mission Viejo. The idea is that the sterilized male mosquitoes, which don’t bite, will outcompete the non-sterilized males to lower West Nile-carrying populations.

But the Vector Control District is also urging residents to take their own precautionary measures.

“We’re trying to teach people to look for in and around their homes, anything that can hold standing water,” he said, adding that buildup often happens around neighborhood curbs, backyard water hoses, garden ponds, atop pool covers and in crawl spaces.

“And if everybody did that, the world would be a beautiful place,” Brannon said. “But it takes vigilance.”

How can we ward off bites?

• Remove stagnant water from homes and backyards. And at least once a week, clean any containers that hold water, including pet bowls, bird baths, flowerpot saucers and trash containers.

• “Mosquitoes that carry West Nile virus, they bite at dusk and dawn,” Brannon said. Wear loose-fitting long pants, long sleeves and light-colored clothing. Mosquitoes can bite through fitted clothing, such as yoga pants.

• Use screens, windows and doors, and if available, use air conditioning.

• Carry and wear EPA-registered repellents.

• Report dead birds to the Vector Control District to help officials track West Nile.

• Report high mosquito activity or causes such as standing water to the Vector Control District at ocvector.org.

The agency offers free mosquito control services, Brannon said. “It’s a first come first serve type of thing.”

“So if people are seeing mosquitoes or home issues and they want us to come out, better call now,” he said, “because it looks like we’re going to be pretty busy throughout the summer.”

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Cities where infected mosquitoes have been reported

• Anaheim
• Brea
• Buena Park
• Cypress
• Costa Mesa
• Fullerton
• Garden Grove
• Huntington Beach
• Los Alamitos
• La Habra
• Newport Beach
• Orange
• Santa Ana
• Seal Beach
• Stanton
• Westminster