NEW YORK – On a steamy Wednesday evening, a South Brooklyn intersection was quiet except for distant flashing lights. A subtle buzzing noise grew louder as a convoy of vehicles crawled past two-story homes.

Then, a loudspeaker from a New York City health department vehicle announced along Bay Ridge Parkway.

“The city is spraying pesticide to reduce the risk of the West Nile virus,” a recorded male voice stated. “To limit exposure, please stay indoors until the trucks have left the area.”

Inside their air-conditioned homes, many residents were likely unaware that health officials had detected West Nile-infected mosquitoes just a few blocks away near Dyker Beach Golf Course in late August.

The end of summer marks peak mosquito season. Twenty-five years ago, West Nile virus was first identified in the Western Hemisphere in New York City before it spread across North America. To combat this, public health officials regularly spray pesticides to eliminate Culex mosquitoes before they can spread the virus to humans. However, increasing temperatures in recent years have made it easier for mosquitoes to breed and spread diseases, presenting new challenges for health departments to protect the public from illness and mortality.

Conditions Favoring Mosquitoes

At the rear of the convoy, a white Ford pickup truck approached the intersection. A green fogging machine on the flatbed released a mist that quickly vanished into the evening air. The team sprayed the equivalent of a teaspoon of Duet, a pesticide designed to kill adult mosquitoes, over each acre in several middle-class Brooklyn neighborhoods close to the Atlantic Ocean.

The loudspeaker announcement and pesticide spraying elicited varied responses. As the truck passed, a man across the street recorded the moment on his phone. Just feet away from the spraying, a food delivery rider zipped by on his scooter.

On any summer day, the city’s Department of Health and Mental Hygiene sets out at least 50 traps across all five boroughs, with each trap capable of capturing up to 1,000 mosquitoes.

In late August, city teams were intensely focused on combating mosquitoes. Workers endured countless bug bites while health department maps confirmed the presence of mosquitoes testing positive for West Nile throughout the city. Six residents were infected this year, one of whom was hospitalized.

Certain weather conditions are ideal for pest control, according to Hamiltan Simean, an entomology associate with the health department, who mentioned, “Today’s excellent weather.” The heat index climbed above 100 degrees. Simean frequently wiped his brow while demonstrating various mosquito traps to reporters.

From the back of a Toyota Prius, he and his colleague, Zurina Yusoff, presented a sample of a foul mixture of rabbit food and water, which serves as a breeding ground for Culex mosquitoes to lay their eggs. In this gravity trap, mosquitoes are attracted into a bucket containing the “nasty water,” Yusoff explained. A fan then propels them into a net.

The following morning, teams collect the trapped mosquitoes and store them in red gallon coolers filled with dry ice to preserve any viruses for laboratory analysis. Near the golf course, around 40 pools of mosquitoes—each containing up to 50 insects—had tested positive for West Nile. Using these results, staff traveled through neighborhoods, spraying dense populations with the cannon. In less accessible areas, like wetlands or parks, the health department employs a helicopter for spraying.

“Our primary goal is to prevent the transmission of disease to humans,” Dr. Waheed Bajwa, executive director of the city’s Office of Vector Surveillance and Control, explained at dusk in the parking lot of the Brooklyn golf course. “That’s why we are here.”

Two days later, only two mosquito pools returned positive tests.

West Nile’s Arrival

Back in August 1999, a strange illness affected several individuals in Queens, presenting symptoms like encephalitis, which is brain inflammation, as reported by the U.S. Centers for Disease Control and Prevention (CDC). Initially, doctors suspected it was St. Louis Encephalitis, another illness spread by mosquitoes. Tragically, seven people lost their lives, and over 60 others contracted the disease.

State health officials, unable to identify the source of the illness, sent brain tissue samples from three encephalitis cases to Dr. Ian Lipkin’s lab at the University of California, Irvine. Through genetic sequencing, Lipkin discovered that the patients were infected with the West Nile virus, which can lead to severe neurological issues in some cases.

It’s still a mystery how the West Nile virus, named after a region in Uganda, made its way to the United States. Since mosquitoes have a limited flying range, scientists hypothesize that infected birds or mosquitoes may have traveled on a flight from the Middle East or Africa, where the virus is common.

“This was a pivotal moment,” Lipkin, now the John Snow professor of epidemiology at Columbia University’s Mailman School of Public Health, remarked to YSL News. “We observed the virus spreading across the U.S. But back then, the big question was how long it would take to reach other areas.”

Initially, authorities believed they could contain the virus within the New York area. However, when infected mosquitoes were discovered in Central Park, city officials closed off access at night, and the New York Philharmonic canceled a scheduled concert, according to the New York Times.

Dr. Lyle Petersen, who leads the CDC’s vector-borne disease division out of Colorado, recalled expanding his search for infected mosquitoes beyond a 20-mile radius from New York City to a 60-mile radius after realizing the seriousness of the situation.

This approach, Petersen admitted, was overly simplistic. The primary hosts for West Nile were birds rather than mosquitoes. While mosquitoes can only fly limited distances, migratory birds can cover hundreds of miles. Culex mosquitoes, which are widespread across the U.S. before the virus appeared, could have bitten infected birds from afar. Once they consumed the virus-laden blood, they could transmit the disease to humans.

Before long, West Nile showed up in Petersen’s own mailbox, 1,600 miles away in Colorado. In July 2003, while chatting with a neighbor about West Nile after work, he learned about dead birds found at a nearby lake, indicating the virus had reached the area. Unfortunately, he wasn’t wearing insect repellent, and after getting bitten by mosquitoes, he quickly went inside. By then, it was too late.

Just three days later, on his birthday, Petersen went for a run. Usually energetic as a marathon runner, he struggled just two miles in, feeling fatigued and achy.

A few days later, he experienced difficulties with bright lights and developed a stiff neck, raising suspicion of meningitis, a possible symptom of the neuroinvasive form of West Nile. Ironically, the West Nile expert became the first documented human case in Larimer County. He continued to feel fatigue for months during meetings regarding the virus’s impact.

The virus moved across the Rocky Mountains to the Pacific Coast and into the deserts, where it remains prevalent. In 2003, over 9,860 individuals contracted the virus, including Petersen. More than 260 died from the infection.

Since then, the virus has appeared in waves. Petersen acknowledged that the most reliable indicator of an outbreak is if there has been a prior outbreak, which isn’t particularly helpful.

Infections typically begin to rise in late summer. Current CDC data indicates that in 2024, there have been 377 West Nile cases, with 255 being classified as neuroinvasive.

While surveillance and mosquito-spraying efforts have improved, the effectiveness of these measures can differ greatly by location, Petersen noted. For instance, New York City is more proactive compared to other areas, where West Nile cases are significantly underreported or misdiagnosed. Most individuals infected show no symptoms, while others experience mild ailments like fever and body aches.

Currently, there is no vaccine available for humans against the West Nile virus.

Impact of Climate Change on Virus Spread

To complicate matters, climate change has expanded the reach of mosquitoes and the diseases they carry, Petersen explained. In warmer conditions, mosquitoes not only become infectious more quickly, but they become more efficient at spreading disease. Climate change accelerates these processes.

Dr. Peter Hotez, the dean of Baylor College of Medicine’s National School of Tropical Medicine in Houston, pointed out that rapid urban development enables mosquitoes to easily infect large populations of humans. Issues like poverty worsen public health problems, including poor drainage systems that create ideal habitats for mosquitoes, as well as homes lacking window screens or air conditioning that allow mosquitoes to enter and bite people.

According to Hotez, these factors are already significant issues, but they are expected to escalate into major public health challenges in the years ahead.

Petersen is concerned that complacency has set in among the public. What was once perceived as an exotic tropical disease has become normalized.

“People have adjusted to its presence,” he noted. “They no longer take necessary precautions to avoid infection.”

“Many think, ‘It won’t happen to me,’” he added.

Returning to Brooklyn

Recently, Dr. Anthony Fauci, who played a key role in the initial federal response to the COVID-19 crisis, ended up in the hospital due to West Nile virus. He mentioned to CBS that he probably got bitten in his backyard in Washington, D.C. and described his experience to STAT as the worst he has ever felt.

The 83-year-old physician was raised in Brooklyn, not far from where the virus has now been detected near the Dyker Beach Golf Course.

As the sun dipped below the horizon on the final hole, on the date of the treatment, John Lepore, 73, and Riccardo D’Orazio, 71, placed a small wager while standing by the edge of the green. The two retirees had enjoyed a day of golf and returned for their last shot, each putting down a dollar bill on the ground. The player who got their ball closest to the hole would win the other’s dollar.

With insects buzzing around the green, the men assessed whose ball was nearer. They didn’t recall being bitten by any mosquitoes and mentioned they hadn’t applied any repellent.

Meanwhile, city workers were preparing a truck to spray pesticide throughout the area. They planned to keep spraying until daylight. If they found more mosquitoes carrying the West Nile virus, they would repeat the process.