In a Decaying Queens Fortress, It’s One Man Versus 47 Kinds of Mosquito

In a damp, dungeonlike cell beneath a crumbling military fortress in northeast Queens, Dr. Waheed Bajwa and his team were counting sleeping mosquitoes and trying to divine the future.

Soon the mosquitoes would awaken and secrete rafts of goo into puddles of standing water and lay hundreds of eggs onto them that would hatch into larvae that would feed and grow up and mate and lay eggs of their own — until sometime in late summer one of their great-great-great-great-great-great-great-great-great-great-granddaughters would bite a sparrow infected with West Nile virus and then, perhaps, a human.

But that day was months off. On this balmy morning in mid-February, Dr. Bajwa, a mild-mannered, methodical, relentless medical entomologist who has spent 21 years heading the city Health Department’s Office of Vector Surveillance and Control, was hoping to find signs that the coming summer would be merciful.

Last year saw the highest number of human West Nile cases since 1999, when the virus first appeared in the Western Hemisphere in Queens and killed four New Yorkers.

Now, in the city’s 25th year living with the virus, Dr. Bajwa was chasing the goal he had never achieved: to make it through an entire New York summer without a single human case of West Nile.

Dr. Bajwa’s war against mosquitoes and West Nile is waged by air and ground, from the swamps of Staten Island to the manholes of the Upper West Side. His weapons include dry ice and bacteria-impregnated corncob granules, fermented rabbit chow, copper BB pellets and a device called a Multi-Tube Vortexer.

In the dripping cell in Queens, Dr. Bajwa pointed a flashlight at the 300 mosquitoes clinging to the ceiling of Entrance 1, Room 3 of the city’s official mosquito hibernaculum and pronounced the early results encouraging: “If we would have come last year, there would be thousands actually in one single room.”

New York City, with its 5,600 acres of wetlands, 150,000 storm drains and miles of ancient sewer tunnel, is a sprawling mosquito paradise. It is home to 47 species of Culicidae, including two that were first recorded in the United States in Dr. Bajwa’s 2018 study, “A Taxonomic Checklist and Relative Abundance of the Mosquitoes of New York City.” The paper revealed that 21 new species had taken up residence here since the last survey in the 1930s.

There are bluish mosquitoes, golden mosquitoes, striped mosquitoes, spotted mosquitoes, mosquitoes with apt species names like Aedes excrucians and Aedes vexans. But none preoccupy Dr. Bajwa, 64, as much as the most common species, Culex pipiens, the northern house mosquito — the biggest source of West Nile infection in New York.

West Nile is typically transmitted to humans this way: A bird that has the virus is bitten by a mosquito. Then the mosquito, now a carrier, bites a human.

In some parts of the country, house mosquitoes feed primarily on birds. But the New York City version is a hybrid between a subterranean strain, which developed a taste for mammalian blood from sewer rats, and the more common aboveground version that prefers birds. This makes it a perfect “bridge vector” — an agent that spreads disease from one species to another.

Last year, Dr. Bajwa believes, a new strain of West Nile emerged that birds had not had time to build immunity to, so more birds contracted the virus. The infected birds passed the strain to city mosquitoes, who passed it on to 46 humans, more than double the typical number. Two people died.

West Nile has killed 59 people in New York City over the years. More than 400 people have contracted West Nile neuroinvasive disease; its symptoms include brain inflammation, paralysis and permanent nerve damage. The city estimates that there have been 12,000 undiagnosed cases of West Nile fever.

The mosquito campaign begins each winter in the Queens hibernaculum, a warren of nine dismal rooms beneath a 120-year-old gun battery at Fort Totten Park that disuse has transformed into a laboratory: Each room has different light, temperature and humidity conditions, making the fortress an ideal place to observe and model winter survivorship rates and allowing the city to get a jump on forecasting the coming season. Some hibernating mosquitoes turn out to have West Nile hibernating inside them.

The battle reaches its fiercest stage in late August, when the infection rate in mosquitoes peaks and the most human cases develop. Trucks sweep through residential neighborhoods spraying pesticide.

There has never been a year with fewer than three human cases. If the city lets up the pressure, Dr. Bajwa said, “the number of cases is going to go very high.”

‘They look beautiful’

Dr. Bajwa discovered the joys of entomology growing up in Pakistan, where his father, the agriculture director in the mountainous province of Azad Kashmir, took him to the lab and on nature walks. His first insect loves were dragonflies and butterflies, but he has grown to admire mosquitoes, even though his job requires that he slaughter them by the millions.

“If you look at them under the microscope, oh, they look beautiful — I will show you!” Dr. Bajwa said. “Their antennas. Their eyes, their compound eyes, their mouthparts.”

Some are particularly striking. Under a microscope, Psorophora ferox, the white-footed woods mosquito, found occasionally on Staten Island, is a riot of iridescent color, purple and green and gold, as if it had been showered with pixie dust.

Dr. Bajwa is particularly fond of the elephant mosquito, Toxorhynchites rutilus, one of the largest species in the United States, half an inch long, with dapper, blue-speckled legs. “Those are a favorite because they feed on other mosquitoes,” he said.

In late spring, the city starts bombing breeding grounds with larvicide — ground-up corncobs saturated with naturally occurring soil bacteria that are deadly to baby mosquitoes but generally harmless to other life.

Dr. Bajwa oversaw the operation at Freshkills Park on Staten Island, a savannah of gentle hills laid atop what was once the world’s largest landfill. It was June 8. A helicopter roared in, refilled with pesticide, took off again. The pilot, John Sondgeroth, a Vietnam combat vet, flew low over Fresh Kills creek, strafing the waterline, targeting the roots of marsh grass where another species that carries West Nile shelters and feeds.

‘Just like mowing the lawn’

“Just like mowing the lawn,” Mr. Sondgeroth said. “You go back and forth, back and forth, back and forth.”

The Health Department conducts larviciding citywide near the start of the season to cut the overall population. It limits its spraying for adult mosquitoes, which involves less environmentally benign chemicals, to neighborhoods where virus activity is high, later in summer. Mosquitoes grow up fast, progressing from larva to expectant mom hungry for blood in a couple of weeks.

Near Freshkills, Dr. Bajwa led a brief side expedition to a marshy thicket across from an Amazon warehouse, one of more than 400 spots where the Health Department sets mosquito traps. His assistant director for vector surveillance, Kamesan Kanapathipillai, ducked behind a tree and emerged with an apparatus that looked like a homemade lamp attached to a tray of slimy liquid.

This was a trap for pregnant mosquitoes. The lure was a slosh of water into which rabbit-food pellets are dissolved and left to rot, simulating the puddles and ponds rich in decaying plant matter where mosquitoes lay their eggs.

A fan mounted above the water sucked the mosquitoes — there were hundreds — into a mesh cage. Mr. Kanapathipillai transferred them to a cooler of dry ice, killing the mosquitoes while keeping any virus inside them alive.

The mosquitoes would be tested in the city’s public health lab, in groups of 50, known as pools. In a typical year, about 700 mosquito pools test positive for West Nile, out of about 5,000. Last year the city found 1,555 positive pools, the most it has ever recorded.

Your chances of getting West Nile depend on where you live, because different species dominate different neighborhoods. The common house mosquito is found in a crescent stretching from eastern Queens to southern Brooklyn to the east tip of Staten Island. Staten Island is also thick with unbanded salt marsh mosquitoes.

Then there is Dubos Point Wildlife Sanctuary, a mosquito playground in Far Rockaway, jutting into Jamaica Bay, where the Health Department is not allowed to spray. It is the domain of the black salt marsh mosquito. They do not carry West Nile but are terrifying nonetheless. At Dubos Point, Dr. Bajwa’s vector surveillers set their traps and run.

“You can’t get away,” Mr. Kanapathipillai said. “Your face, up your nose, your mouth, your ears.” A single trap set in Dubos can capture 5,000 mosquitoes in 24 hours.

A field trip to the sanctuary confirmed that life there is wild indeed. On the trail that skirts the marsh grass, a dense cloud of bloodlust envelops the visitor. Hundreds of tiny needles penetrate all exposed flesh.

‘Weak fliers’

I had let Dr. Bajwa know that I planned to head out to Dubos Point. He emailed me that afternoon: “I just wanted to reach out and inquire about your experience in the Dubos Point marshland. While I trust that your time in the marshland was enjoyable, I wanted to take a moment to address any potential challenges or unexpected situations that may have arisen during your trip.”

I mentioned that I got bit dozens of times in a matter of minutes. Dr. Bajwa, whose personal mosquito control plan includes wearing long sleeves even on the hottest days of midsummer, sent a link to the CDC’s mosquito bite symptom and treatment page. “Thank you once again for sharing your experience,” he wrote. “If you have any further questions or need additional information, please don’t hesitate to reach out.”

He has his own method of dealing with mosquitoes. “When I find myself relaxing in my backyard, I always set up a pedestal fan,” he wrote. “Mosquitoes happen to be weak fliers, unable to contend with even a gentle breeze.” When he does get bitten, he added, “I make a conscious effort not to give in to the temptation of scratching.”

The Office of Vector Surveillance and Control is quartered on the 11th floor of the city’s Public Health Laboratory, a drab bastion of bureaucracy on First Avenue in Manhattan.

Each weekday in the summer, the contents of dozens of traps around the city are brought in to the office and processed. During a two-day period in July, Mr. Kanapathipillai and a colleague, Hazel Paul, sitting at their microscopes, identified and logged 26,000 individual mosquitoes.

After the species that carry West Nile are sorted into tubes of 50, two BB-gun pellets are placed in each tube. The tubes are sent down to the testing lab on the ninth floor where they are agitated in the Vortexer, a high-speed mixer, until the mosquitoes are pulverized. Then they are centrifuged to extract any West Nile RNA.

The office, which has an annual budget of $4 million, was created in 2001 as part of the city’s response to West Nile. The disease was first identified here after an 80-year-old man in northern Queens died in late August of 1999 of what was initially misdiagnosed as St. Louis encephalitis.

Within two months, 44 people had been hospitalized, and three more were dead. The city’s mosquito control apparatus, which Dr. Bajwa said had been largely dormant since the 1970s, was resurrected. There was considerable public alarm. Mayor Rudolph W. Giuliani held frequent news conferences to announce setbacks and advances in the fight. When Central Park closed overnight for spraying after the virus was found there, it was front-page news.

‘A lethal disease’

A large-scale epidemic never happened, which Dr. Bajwa attributes to the city’s aggressive tactics and speedy testing operation.

“Within 24 hours, we are able to figure out where the virus is circulating in the city of New York, and we immediately we go there and we start doing larviciding,” he said.

Dr. Bajwa urged against complacency at all costs. “West Nile virus is a lethal disease,” he said.

On Aug. 3, Dr. Bajwa stood in the parking lot of Baisley Pond Park in southeast Queens, a mile from Kennedy Airport. No human case had been recorded in the city, but it was early, and the results from the mosquito traps were concerning.

“We have a very high level of West Nile virus in this area,” he said gravely.

It was just before sunset. The park was emptying out, but the parking lot was filling up with Health Department pickup trucks. Mounted in the bed of each was a Grizzly Ultra Low Volume Fogger Sprayer.

The city sprays residential neighborhoods with Anvil pesticide, which can irritate people’s respiratory systems and harm aquatic life, only as a last resort, Dr. Bajwa said. But the park and the area around it met the threshold: positive pools at numerous locations and several weeks of “persistent positivity.” (A city environmental impact study in 2001 found the effect of pesticide minimal compared with the risk from West Nile.)

As the trucks set out, loudspeakers mounted on escort cars blared a warning: “To minimize exposure to the pesticide, please go indoors immediately until the trucks have passed.”

Luke Howell, a veteran exterminator, flipped a switch by the dashboard of his truck.

“OK, I’m flowing,” he said. A plume of fog issued from the sprayer. Back and forth, back and forth, back and forth. The truck crept past silent lawns and driveways. Up 121st Avenue. Down 217th Street. As Mr. Howell approached a couple standing by their car, he turned off the sprayer. The couple pulled their T-shirts up over their noses. Mr. Howell passed by and turned the spray back on.

The trucks would be out until 2 or 4 a.m. Dr. Bajwa went home to sit at his computer and wait for a possible call. “I’m home, but I don’t sleep,” he said. The next day would be busy: “I have been told by our public health laboratory that we have 78 new positive reports.”

The streak continued: more positive pools — the count passed 500 — but no human cases.

In the fourth week of August, bad news trickled in.

Two people in Queens had contracted West Nile. So had someone in Manhattan. By Aug. 28 there were half a dozen cases.

Dr. Bajwa had known a year without any human cases was an elusive goal. “The chances for that to happen are very low,” he said.

In his office on First Avenue, Dr. Bajwa studied maps and sifted data. There were more traps to set, more neighborhoods to spray. The distant descendants of February’s mosquitoes were thick in the air, and the season still had two months to go.