With summer temperatures giving way to cooler weather, you may see less mosquitoes buzzing about, but experts say August and September is when mosquitoes are most likely to carry West Nile virus.
“Even though the mosquitos are declining, we’re still seeing the virus,” said Philip Armstrong, chief scientist at the Connecticut Agricultural Experiment Station’s department of entomology. “A lot of them are carrying the virus right now. So we’re at a period of peak risk.”
Connecticut’s first known case of West Nile virus this year was reported by the state in September. According to the Department of Public Health, a man in Fairfield County became sick with West Nile virus in August and required hospitalization, but has since recovered.
About 2,000 people across the United States contract West Nile virus every year, according to the Centers for Disease Control and Prevention. Most people won’t develop symptoms, but in very rare cases, the virus can be deadly. More than 3,000 people in the U.S. are known to have died from the virus since it first arrived in the country in 1999.
“It's now the most important mosquito borne disease in the United States, and it is not going anywhere,” Armstrong said.
How mosquitoes are tested and collected
The Connecticut Agricultural Experiment Station has been tracking mosquitos for viruses since 1997. The station’s lab in New Haven was the first to detect West Nile virus in mosquitoes in North America in 1999.
From June to October, the station collects an average of 300,000 mosquitoes and employs about a dozen seasonal workers to collect, identify and prepare them for testing.
Liz Triana is one of the lab’s mosquito trappers. Every morning, she drives to parks across Connecticut, often at the crack of dawn, and makes a beeline for the park’s bushes and shrubs, where she sets mosquito traps.
“This is our light trap,” she said on a recent morning, pointing to what looks like a giant bird feeder, tucked away in the bushes of Beaver Pond Park park in New Haven. A bag of dry ice sits at the top of the trap, giving off carbon dioxide, like humans do.
“That's what mosquitoes are drawn to, they sense that,” Triana said.
The dry ice, and a light below the ice, attract the mosquitoes. Once they get close, a fan sucks them in and pushes them downward, where they get trapped inside a mesh bag. Triana comes back the next day to collect her buzzing victims.
“This is looking pretty good. So maybe 50, 25 to 50 in here, probably more than that,” Triana said.
Triana then drives the mosquitos to the station’s lab in New Haven where mesh bags from the traps are emptied out onto large trays for sorting. Only the female mosquitos, which are known to carry viruses, are tested.
Olivia Buchler, one of the lab’s assistants, was bent over a tray of insects, sorting through them with tweezers, during a recent September morning. When she describes her job to people, she said, she sometimes gets met with skepticism.
“They think it's a joke at first,” Buchler said. “But it's been cool because, I don't know, I really like doing science for people.”
And, she said, it’s especially gratifying when friends and family members see stories about West Nile virus on the news.
“And they’re like, ‘Oh, is this the thing that you're working on?’ I'm like, ‘Yeah, that is the work that I do every day,’ Buchler said. “It's definitely an untraditional job, but that's what makes it pretty exciting.”
Once the mosquitoes are sorted, they’re identified under a microscope and put into test tubes, each containing up to 50 mosquitoes. The test tubes are taken to a high security lab where the mosquitos are ground up into a fine mosquito slurry.
“The way we do that is we have this machine here. It's called the mixer mill. It looks like a paint shaker,” Armstrong said.
The machine shakes the test tubes vigorously, each one containing a projectile BB inside.
“The BB just macerates the mosquitoes inside,” Armstrong said.
The slurry is then tested in cell culture to test for viruses. Out of thousands of mosquitos collected by the lab each year, approximately 200 will test positive for West Nile virus.
“The probability of that mosquito being infected is low, but when you’re in a large state, there’s still plenty of opportunity for human infection given how many people there are and how many bites we receive,” Armstrong said. “With mosquito-borne diseases, it’s a numbers game.”
How climate change could increase the risk for West Nile virus
As temperatures rise from global warming, climate change is giving mosquitos and West Nile virus a couple of advantages. Milder winters are extending the mosquito season, meaning mosquitoes can stick around for longer, according to Armstrong. Data from the Connecticut Agriculture Experiment Station also shows new mosquito species are coming to Connecticut, ones that were not able to previously survive New England winters.
Hotter summers, on the other hand, allow mosquitos to reproduce faster. West Nile virus can also replicate faster under warmer temperatures, leading to increased risk.
“Mosquitoes have very boom and bust life cycles, and so they can increase very rapidly if the conditions are favorable,” Armstrong said.
Researchers in Connecticut will continue to test for viruses until mosquitos die during the first hard freeze, which should be sometime in October.
Áine Pennello is a Report for America corps member who covers the environment and climate change for Connecticut Public.
