The 25-year fight to defeat West Nile virus, one convoy at a time.

NEW YORK – On a muggy Wednesday night, the South Brooklyn intersection was still except for distant flashing lights. A faint buzzing grew louder as a convoy of vehicles inched past two-story homes.

Then a loudspeaker on a New York City health department vehicle boomed down Bay Ridge Parkway.

“The city is applying pesticide to reduce the threat of the West Nile virus,” the recorded male voice blurted. “To minimize exposure to the pesticide, please go indoors immediately until the trucks have passed.”

Inside their air-conditioned homes, many residents likely didn’t know that health officials had found mosquitoes infected with West Nile a few blocks away near Dyker Beach Golf Course in late August.

Late summer is peak mosquito season. Exactly 25 years ago, West Nile first appeared in the Western Hemisphere in New York City before it spread across North America. Public health officials have adapted by spraying pesticides to kill off Culex mosquitoes before they can infect people with the virus. But warming temperatures in recent years have made it easier for mosquitoes to multiply and spread diseases. Health departments face new challenges in protecting people from illness and death.

Mosquito weather

In the back of the convoy, a white Ford pickup approached the intersection. A green cannon on its flatbed shot a fog that quickly dissipated in the night air. The crew sprayed the equivalent of a teaspoon of Duet, a pesticide that kills adult mosquitoes, for every acre in a handful of mostly middle-class Brooklyn neighborhoods near the Atlantic Ocean.

The loudspeaker and spraying drew mixed reactions. As the truck passed, a man across the street recorded video on his phone. Just feet from the pesticide vapor, a food deliveryman zipped by on a scooter.

On a given summer's day, the city Department of Health and Mental Hygiene has at least 50 traps in place across the five boroughs for officials to collect and test mosquitoes for diseases, including West Nile. Each trap catches up to 1,000 mosquitoes.

In late August, city teams were at their busiest fighting mosquitoes. Workers have countless bug bites. Health department maps showed mosquitoes recently tested positive for West Nile across the city. Six people were infected this year, officials said. One person was hospitalized.

Certain conditions make for ideal pest fighting, said Hamiltan Simean, an entomology associate for the health department, noting that “today’s great weather.” The heat index surpassed 100 degrees. Simean periodically wiped his brow as he showed reporters different mosquito traps.

From the back of a Toyota Prius, he and his colleague, Zurina Yusoff, offered a whiff of a festering mix of rabbit food and water, the kind of putrid liquid where Culex mosquitoes lay their eggs. In this gravity trap, they are drawn into a bucket filled with the "nasty water," Yusoff explained. A fan then blows them up into a net.

In the morning, teams collect caught mosquitoes and store them on dry ice in red gallon coolers, which preserves any virus they might have for lab testing. Near the golf course, around 40 pools of mosquitoes ? up to 50 insects per pool ? had tested positive for West Nile. Based on these results, staff drove through neighborhoods and sprayed densely populated areas with the cannon. In secluded areas, such as wetlands or parks, the health department uses a helicopter.

“We just want to make sure we prevent the spread of disease to humans,” Waheed Bajwa, executive director of the city’s Office of Vector Surveillance and Control, said at dusk in the Brooklyn golf course parking lot. “That’s why we are here.”

Two days later, only two pools tested positive.

West Nile arrives

In August 1999, several people in Queens came down with a mysterious illness, with symptoms that included encephalitis, or brain swelling, according to a U.S. Centers for Disease Control and Prevention report. Doctors thought it was St. Louis Encephalitis, another mosquito-borne illness. Seven people died and more than 60 were infected with the illness.

State health officials, unable to determine what was making people sick, sent brain tissue samples from three encephalitis cases across the country to Dr. Ian Lipkin's laboratory at the University of California, Irvine. Using sequencing, Lipkin found the patients had West Nile, which can cause neurological damage in extreme cases.

It's unclear how West Nile, a virus named for a region in Uganda, arrived to the U.S. Mosquitoes can only fly short distances. However, scientists believe infected birds or mosquitoes boarded an airline flight from the Middle East or Africa, where the disease is endemic.

“It really was a catalytic event,” Lipkin, now the John Snow professor of epidemiology at Columbia University Mailman School of Public Health, told USA TODAY. “We watched it march across the United States. But at that time, the question was, how long was that going to take?”

Officials assumed they could could contain the virus to the New York area. When infected mosquitoes were caught in Central Park, city officials closed night access and the Philharmonic canceled a concert, The New York Times reported.

Dr. Lyle Petersen, director of CDC’s vector-borne diseases division, which is based in Colorado, recalled driving a 20-mile radius outside New York City to find infected mosquitoes. Then he expanded to 60 miles.

That strategy proved naive, Petersen said. Birds were West Nile's primary reservoirs, not mosquitoes. Unlike the tiny mosquitoes, migratory birds travel hundreds of miles. Culex mosquitoes, found throughout the U.S. before the virus entered, could bite infected birds that had flown long distances. After ingesting blood with virus, mosquitoes could then spread it to humans.

West Nile soon wound up at Petersen’s mailbox, 1,600 miles away in Colorado. In July 2003, Petersen was chatting with a neighbor after work about West Nile. Birds had been dropping dead that year at a nearby lake, which Petersen said indicated the virus had arrived. Petersen wasn't wearing repellant. He and his neighbor noticed mosquitoes biting them so they went indoors. By then, it was too late.

Three days later, Petersen went for a run on his birthday. As a marathoner, he recalled having no energy just 2 miles into his run. His muscles ached and he felt feverish.

Days later, he had trouble seeing bright lights. He developed a stiff neck, which he thought could be meningitis, a symptom of the neuroinvasive form of West Nile. The West Nile expert, strangely enough, became the first reported human case in Larimer County. Months later, during meetings about the disease's effects, he still felt fatigue.

The virus crossed the Rocky Mountains to the Pacific and the desert, where it continues to circulate. In 2003, more than 9,860 people became infected, including Petersen. More than 260 died.

In the years since, the virus has come in spurts. The best predictor of an outbreak is if there has been a previous outbreak, which isn't terribly useful, Petersen admits.

Infections start getting identified in late summer. In 2024, 377 people have been infected with West Nile, latest CDC data shows. Among those were 255 neuroinvasive cases.

Surveillance and spraying have become more consistent but abatement varies by jurisdiction, Petersen said. New York City, for example, is more aggressive. Other regions are less so, and cases of West Nile virus are vastly underreported and undiagnosed. Most people who get the infection don't show any symptoms. In others, the disease presents as fever and body aches.

There is no human vaccine against West Nile.

A warming climate threatens spread

To make matters worse, climate change has increased the reach of mosquitoes and diseases they carry, Petersen said. In warmer climates, mosquitoes not only become infectious faster, they also become more infectious. Climate change hastens this.

Dr. Peter Hotez, dean of Baylor College of Medicine's National School of Tropical Medicine in Houston, noted that rapid urbanization allows mosquitoes to spread the disease among plentiful human subjects. Poverty creates additional concerns to public health, including inadequate drainage that fosters environments for mosquitoes and homes without window screens or air conditioning that allow insects to enter and infect people easily.

These are “already starting to become significant problems,” Hotez said. “But these are going to become major climate health threats in the coming years.”

Petersen worries people have become complacent. West Nile was once considered exotic, a tropical disease new to the hemisphere.

“Then people got used to it,” he said. “They don’t take the precautions they need to prevent from getting infected."

"People think, ‘Well, it’s not going to be me,’” he said.

Back in Brooklyn

Recently, Dr. Anthony Fauci, who helped guide the early federal response to the COVID-19 pandemic, was hospitalized with West Nile virus. He told CBS he’d likely been bitten in his backyard in Washington, D.C., and described it to the health and medicine news outlet STAT as the worst he'd ever felt.

The 83-year-old physician grew up in Brooklyn, blocks from where the virus showed up near the Dyker Beach Golf Course.

As the sun set on the 18th hole, on the day of the convoy, John Lepore, 73, and Riccardo D’Orazio, 71, placed a bet as they stood at the edge of the green. The retirees had played a full day and returned to the final hole and dropped $1 bills on the grass. Whoever putted their ball closer to the hole would take the other man's dollar.

Bugs fluttered around the green as the men measured whose ball was closer. Neither recalled getting bitten by mosquitoes. Neither had used repellant, they said.

Behind them, city staff readied the truck's cannon to spray pesticide. Teams would continue spraying until daylight. The next time they caught mosquitoes infected with West Nile, they'd do it again.

This article originally appeared on USA TODAY: West Nile virus spreads in peak season. Climate change makes it worse