Early, intense West Nile season may signal a severe year for the mosquito-borne illness, CDC says

By Brenda Goodman, CNN

(CNN) — Much of the country is sizzling under record heat, but Dr. Peter Hotez, an infectious disease specialist in Houston, is heading out for his early morning walks as covered up as possible in a t-shirt, a hooded sweatshirt, a hat, sweatpants, socks and sneakers.

It’s not the heat he worries about so much as the mosquitoes.

“My neighbors look at me like I’m absolutely nuts the way I’m dressed in this hot weather, but I don’t want to get what Tony got, which is pretty severe illness if you’re over 65 from West Nile,” said Hotez, director of the Center of Vaccine Development at Texas Children’s Hospital.

“Tony” is Dr. Anthony Fauci, former director of the National Institute of Allergy and Infectious Diseases, who wrote about being “the sickest I’ve ever been” after he was infected with West Nile by a mosquito in his backyard in 2024.

Hotez has good reason for caution. According to the US Centers for Disease Control and Prevention, the nation is seeing the earliest start to West Nile virus season in more than two decades.

In a typical year, West Nile cases begin to rise in July and peak in August and September.

But this year as of June 30, states have reported 48 West Nile cases to the CDC, and 38 – nearly 80% – have involved neuroinvasive disease, with which the virus penetrates to the brain. The last time the season started off this early, in 2004, the year ended with more than 2,500 cases and 100 deaths.

This year’s number may not sound big, but most cases of West Nile are never diagnosed since many people don’t develop symptoms that are serious enough to prompt them to seek medical care. The number that is counted tends to be only the most serious cases.

“You can basically multiply that number by 30, and that’s how many people are actually sick,” said Dr. Lyle Petersen, director of the Division of Vector-Borne Diseases in the CDC’s National Center for Emerging and Zoonotic Infectious Diseases.

West Nile activity has been reported in 23 states this year, the highest number this early in a decade, the CDC said. The “activity” metric includes positive tests in mosquitoes and other animals.

Adults over 60, are at higher risk of both the infection and its most severe complications: swelling of the tissues around the brain and spinal cord.

“We’re pretty worried about what’s going to happen,” Petersen said. “And we really want people to think about West Nile and mosquito bite prevention now going forward, because the situation does not look good.”

Petersen isn’t just an expert on tracking West Nile. He also knows the virus intimately. He got the disease while leading the CDC’s incident response to the infection, which first appeared in the United States in 1999, earning him the nickname “West Nile Lyle.”

“I was really sick – I mean really, really sick, sickest I’ve ever been,” Petersen remembered.

“For about 10 days, I was pretty much in bed, though what happened to me after that was, I had about six months of profound fatigue,” he said.

“That was horrible, because we really didn’t know West Nile caused that” at the time, he said. “Even though I was a marathon runner, I could barely walk up the stairs of my house for months.”

Eventually, he recovered. “I was lucky,” he added, noting that many people have complications from West Nile that go on for years.

West Nile virus is cyclical. Cases in humans tend to spike every three years or so, but it’s notoriously difficult to predict when that will happen. Because birds are the primary reservoir for the infection, infecting mosquitoes who then go on to bite humans, scientists believe that West Nile activity has a lot to do with when birds have immunity to the virus and when they don’t.

By far, the hardest-hit area in the US this year seems to be Maricopa County in Arizona, with 29 confirmed cases reported, including four deaths. At the same point in 2025, the county had seen just 13 cases and one death, according to the county Department of Public Health.

“I’d say to your readers and watchers who are in Arizona, particularly around Phoenix, I would be taking mosquito bite prevention seriously,” said Dr. Daniel Pastula, chief of neuro-infectious diseases and global neurology at the University of Colorado-Anschutz and the Colorado School of Public Health.

There are no specific treatments for West Nile virus, Pastula said. Several vaccines have been licensed for horses, and vaccines for humans have been studied in early-stage clinical trials that had promising results, but none has entered late-stage human trials.

Instead, the best protection is vigilant prevention, Pastula said. This includes:

• Eliminating sources of standing water around your home and yard, which serve as mosquito breeding sites.
• Treating water you can’t dump, like ponds and storm drains, with larvicides called mosquito dunks.
• Using traps to lure and capture adult mosquitoes.
• Cooling your home with air-conditioning, leaving windows closed, if possible.
• Repairing damaged window screens.
• Treating clothing and gear with permethrin, a chemical that repels and kills mosquitoes and ticks when outdoors.
• Wearing EPA-registered bug repellents outside, particularly around sunset and sunrise, when mosquitoes are most active.
• Covering exposed skin with long pants and long sleeves when outside.

Finally, Pastula said, the federal government can help by offering more financial support for local mosquito control programs and funding vaccine development.

“Improving support and funding for vaccine development, particularly West Nile virus, is incredibly important to help reduce the burden of disease,” he added.

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