Suffolk's mosquito hunters using traps, samples to monitor for diseases

Scott Campbell, Suffolk County’s chief entomologist, peered at the mosquito trap stationed in the woods near a red maple swamp in Manorville on Friday.

The carbon dioxide emanating from the dry ice attached to the trap did its job, luring in dozens of mosquitoes, which were then contained in a mesh liner.

This is the front line of the county’s battle against mosquito-borne viruses, such as West Nile virus and the rare but even more dangerous eastern equine encephalitis, or EEE.

"The fact that we have so many active mosquitoes in late September means people need to still be careful," Campbell said.

It’s been a busy few months for Campbell and his staff at the county health department’s arthropod-borne disease lab. Mosquitoes infected with West Nile virus showed up earlier and in greater numbers than usual. This month the state declared an imminent threat to public health after an upstate person died from EEE, the first death from the illness in almost 10 years.

"This year has been one of the highest years for West Nile virus," he said. "It seems to be a high year statewide for West Nile and EEE."

So far this season, Suffolk County has found 229 West Nile virus-positive mosquito samples and 16 human cases of the virus in Suffolk County. Those are the second-highest numbers since 2000. In 2010, there were 295 positive samples and 25 human cases.

On average, Suffolk County collects about 137,011 female mosquitoes every season. So far this year, it has collected 146,514.

So far in Nassau County, there have been 15 human cases of West Nile virus and 62 positive mosquito samples.

Courtney Murdock, associate professor in the Department of Entomology at Cornell University’s College of Agriculture and Life Sciences, said having a robust mosquito surveillance program is vital for public health.

"Mosquitoes can be defined as one of the deadliest organisms to humans on the planet because of the diseases they transmit," Murdock said. According to the Centers for Disease Control and Prevention, malaria, for example, killed an estimated 608,000 people in 2022, most young children in sub-Saharan Africa.

She said climate change and other factors can impact the landscape for mosquitoes.

"In the future, we could experience mosquitoes moving around, changing the timing of when they're active," Murdock said. "That could also affect our risk of coming into contact with diseases that are currently circulating here, and maybe diseases that might emerge in the future. If we don't have mosquito surveillance, we can't address any of those problems or anticipate any of those problems in a proactive way."

Surveillance ramps up with West Nile

Suffolk's Department of Health Services started its mosquito surveillance program in the 1970s after EEE was detected in several domestic animals in the county.

While human cases of EEE are rare, about 30% of those who fall severely ill die. Many people who survive a bout with EEE have long-term neurological damage

The surveillance program ramped up after West Nile was discovered in the U.S. for the first time in 1999 in nearby Queens.

While West Nile can cause serious illness, many cases are moderate and some people who are infected experience no symptoms at all. But there are cases every year, and people over the age of 50 are most at risk.

More than 40 traps are set up across the 900-plus sprawling square miles of Suffolk County for surveillance that runs from May through November.

Campbell said the locations are chosen based on history as well as recent monitoring.

"EEE is very specific to red maple swamps," he said. "There’s a species of mosquito in the red maple swamps that drives cycling of the virus — Culiseta melanura."

Meanwhile, another type of mosquito, Culex pipiens, which spreads West Nile virus, is more comfortable laying eggs in pools of standing water, similar to those that can be found around homes.

Two of the traps employed by Suffolk County are designed to attract mosquitoes by honing in on those habits.

The "CDC/CO2 Light Trap" works best to catch Culiseta melanura, the mosquito that keeps the EEE cycle going, as well as a general sample of other mosquitoes in the area. The Culiseta melanura mosquitoes infect birds, and other mosquitoes biting them can infect humans.

It uses a block of dry ice to emit carbon dioxide to trick mosquitoes into thinking they are sensing the exhale of an animal, their next blood meal. Instead they are sucked through a fan into a netted container.

The "CDC Autocidal Gravid Ovitrap" works best to catch Culex pipiens, the species that spreads West Nile virus. These mosquitoes are attracted to the container of fetid water, filed with organic material, to lay their eggs.

Campbell said all female mosquitoes — the only ones that bite people — are tested for pathogens no matter which trap they are caught in.

"We found West Nile at almost every site that we are monitoring for EEE," he said.

After the traps are removed, usually after about a week, they are brought to the lab in Yaphank, where their contents are carefully separated.

Tweezers and mosquitoes

On Friday, entomologist Christopher Romano used a tweezer to separate the female mosquitoes from the males and other insects that were caught in the trap.

He deftly organized them by species — there are more than 50 on Long Island — into labeled petri dishes.

The mosquitoes are counted, and then a portion of the samples are sent to the state’s Wadsworth Center lab in Albany.

Once Wadsworth reports the results of testing, Campbell and others collaborate with Thomas Iwanejko, superintendent of vector control for Suffolk County, to determine if spraying is needed to reduce the number of eggs and young mosquitoes or the adult population.

"We have weekly conference calls," Iwanejko said. "We'll review the site ... Is it wetlands, is it over residential areas?"

The options to spray include using helicopters, trucks or people wearing backpacks. When an EEE-positive sample was found in Connetquot River State Park in Oakdale, Iwanejko said, they wanted to address it right away.

Using a helicopter would have meant getting Federal Aviation Administration clearance and making arrangements with a contractor. Using their own trucks was easier and quicker.

"We could use the road network to get the trails within the park," he said. "We were able to use the trucks to spray within the park. And luckily the numbers went down immediately."

By Lisa L. Colangelo

lisa.colangelo@newsday.com@lisalcolangelo

Lisa joined Newsday as a staff writer in 2019. She previously worked at amNewYork, the New York Daily News and the Asbury Park Press covering politics, government and general assignment.