Mosquitoes Spread Deadly Virus in Multiple States, Cases Surge

August 7, 2026

Health officials are sounding the alarm as the United States faces an explosive surge in deadly mosquito-borne West Nile virus infections.

The Centers for Disease Control and Prevention (CDC) had already recorded 113 human cases by late July, marking the highest midyear total in more than two decades.

However, cases have continued to skyrocket.

Experts warn that the early numbers, combined with an unprecedented rise in infected birds and mosquitoes, suggest the country could be heading into its worst West Nile season since the virus first swept across America in the early 2000s.

“This is the time of year to try to interpret the signals we’re seeing, and I’m seeing reasons for concern,” former Marin County health officer Dr. Matt Willis warned.

“The stars are aligning in a bad way for this to be a worse-than-average season.”

Deadly Virus Spreading Early

West Nile virus is carried primarily by birds and mosquitoes but can spread to humans through mosquito bites.

Most infections cause few or no noticeable symptoms.

However, the virus can trigger a devastating neurological illness in some patients, causing brain swelling, severe muscle weakness, paralysis, and death.

There is no vaccine.

There is no specific treatment.

Texas and Arizona have reported the largest share of cases so far, while California has confirmed seven infections, including two announced Wednesday in Santa Clara County.

That is roughly three times the number California would normally expect at this point in the year.

“These two cases are a reminder that West Nile virus can cause very serious illness,” Santa Clara County Assistant Health Officer Dr. Krishna Surasi said.

“There are steps that the public should take to discourage mosquitoes from feeling welcome.”

Both Santa Clara County patients were recovering at home.

Officials said the cases were unrelated and that both residents had recently traveled elsewhere in California, meaning authorities have not determined where they were infected.

Infected Birds and Mosquitoes Soar

The human case numbers remain relatively low because the most dangerous period of the season usually runs from August through October.

However, surveillance data from animal hosts is already flashing red.

California has identified 251 dead birds infected with West Nile virus, four times as many as at the same point last year.

In Los Angeles County, officials have detected ten times more mosquito pools testing positive for West Nile than they had by this point in 2025.

West Nile circulates between birds and mosquitoes, with humans becoming unintended victims when infected mosquitoes bite them.

“The bird contracts the virus and the mosquito bites the bird and it goes back and forth and occasionally a person gets in there,” Willis explained.

A rapid increase in infected birds and mosquito populations means more opportunities for the virus to spill over into humans.

Arizona Mosquito Samples Test Positive

Arizona officials have also detected a sharp increase in West Nile activity during the state’s monsoon season.

Maricopa County has recorded 183 mosquito samples testing positive for the virus.

Officials operate more than 850 mosquito traps across the county, using dry ice to release carbon dioxide that mimics the breath of animals and attracts mosquitoes.

“We take the mosquitoes that we catch in our surveillance trap and sort them out, and the nighttime-biting mosquitoes are taken over to other parts of the lab and tested for West Nile,” Maricopa County Environmental Services Division Manager John Townsend said.

Townsend said mosquito activity began unusually early because the region experienced a mild winter.

“We started off kind of hot because [in March and April], we really didn’t have a winter,” he said.

“Catching mosquitoes, and they were testing positive already.”

Virus Can Cause Paralysis and Death

West Nile infections can produce fever, headaches, nausea, vomiting, and body aches.

In severe cases, the virus attacks the nervous system.

Older adults face the greatest risk of neurological complications and death, though serious illness can occur in younger people as well.

Stanford infectious disease specialist Dr. Dean Winslow recalled treating an older veteran and farmer from California’s Central Valley who developed severe weakness and paralysis in his legs.

“They do recover, but it takes a while,” Winslow said.

“And people can die of West Nile virus.”

Nearly 10,000 Americans Infected During Previous Peak

West Nile virus was first identified in Uganda’s West Nile region in the 1930s.

It did not emerge in the United States until 1999, when cases appeared in New York City.

By 2003, the virus had reached the West Coast and infected nearly 10,000 Americans nationwide.

The country has averaged roughly 2,000 reported cases annually since then.

Willis warned that the current pace could bring the United States close to levels not seen in 20 years.

“That 20-year [mark] is important because West Nile really only surfaced in the 2000s,” he said.

Officials Urge Americans to Eliminate Standing Water

Health officials are warning Americans to take immediate precautions as mosquito populations rise.

“The main thing is when you’re outside, wear repellent and long-sleeve pants,” Townsend said.

“No one wants to do that in the summer, but anytime they can’t get to your skin, that’s the best option, and number one, get rid of any standing water because that will be where the mosquitoes lay their eggs, and they come out and start biting.”

Residents are being urged to empty pet bowls, plant saucers, inflatable pools, and other containers capable of collecting water at least once each week.

People experiencing unusually high levels of mosquito activity should contact local vector-control authorities.

“The most important thing is avoiding mosquito bites,” Willis warned.

The virus is already appearing earlier and more frequently than expected.

And the most dangerous months of the West Nile season have only just begun.