When Patti Casey traveled to Milton last week to collect mosquitoes from the Agency of Agriculture's traps, she was disappointed to only find one mosquito. As one of four members of the state's team charged with trapping and testing mosquitoes for viruses like West Nile and Eastern Equine Encephalitis (EEE), her time is valuable. One bug isn't much of a sample size, but she brought it back to the state's lab in Berlin along with mosquitoes trapped at other sites in Northwestern Vermont. Much to her surprise, Casey learned a few days later that the single sample she collected in Milton tested positive for EEE.
The mosquito made news this week because it was the first time EEE was found in Chittenden County this year. But Casey was already moving on. On Friday, she was up early and out collecting new samples by 10 a.m. Her first stop was in Colchester. To protect property owners, the Agency of Agriculture does not publicly disclose the locations of traps and only releases results by town.
In her car, Casey keeps a cooler full of dry ice, a pack of nylons, rain boots and a gadget she jokingly calls "The Alanator." Named for State Entymologist Alan Graham, who built it by hand, The Alanator is a vacuum made up of ventilation piping and a kitchen exhaust fan from an RV. It looks like something stolen from the set of a B-movie remake of Ghostbusters, but to this team, it's one of the most important tools in Vermont's arsenal for monitoring the spread of mosquito-borne viruses.
Graham said he built the trap to save time.
"We were using chemicals to kill the mosquitoes in the traps," he said, "and this works much better than that and it's faster."
Time is of the essence. Graham's team of four is responsible for trapping and testing mosquitoes statewide. Because trapping is so labor-intensive, they are only able to monitor the "western corridor" from Rutland County north to the Canadian border.
"It's a tremendous amount of work," he said. "It's hard even with four people. We have very long days."
Graham's exhaustion is understandable. For the past several years, he's made it his mission to trap as many mosquitoes as possible and test them for viruses.
"In previous years, it's just been me looking at mosquitoes in Vermont," he said. This year, as newly-appointed state entomologist, Graham got funding from the legislature to expand the program to four people. The increased staffing has allowed the state to test over 1,000 mosquitoes this year as opposed to just 271 last year, when Graham was working alone.
After Casey fits a nylon stocking over the mouth of the Alanator, she heads into the woods to the resting box traps, which are just that: small, square, black boxes resting on their sides in the woods. Their only purpose is to create a dark place with no wind, which is attractive to mosquitoes. Casey switches on the vacuum, powered by a marine battery she carries in a bag over her shoulder, and holds it into each trap. After she clears out all 10 boxes, she holds up the vacuum and checks the stocking. A small mess of bugs is pushed up against the end of the stocking, powerless to fly against the air current. Casey isn't pleased with her take, but she slips the stocking off the Alanator and carefully rolls it up, trapping the mosquitoes inside.
Next, Casey turns her attention to a more sophisticated trap hanging from a tree branch. The light trap looks like an oddly-designed camping lantern hanging from a thermos with a hole drilled through it. The thermos is empty in the morning, but at night, the dry ice Casey left inside has sublimated (this is what happens when dry ice "melts" from solid to gas), leaking carbon dioxide through the hole at the bottom. The gas attracts mosquitoes, who fly closer and are attracted to a small lightbulb in the trap as well as another, stronger scent coming from a vial inside the mesh netting. The scent: Ox breath. Apparently attractive to the insects, the ox breath smell is generated by a chemical called octenol which is soaked into a cotton ball that sits just below the top entrance of the net trap. Once inside, the mosquitoes are blown down into the trap by a small, battery-powered fan.
Casey takes down the trap, which only has a few mosquitoes in it, and packs it along with the stocking into the cooler of dry ice in her car. Once everything is packed up, she'll continue on to eight other sites and do the same thing again at each one. She'll then bring the samples, labeled in plastic containers, back to the state lab in Berlin. State entomologist Alan Graham and another team member will separate out the mosquitoes likely to be carriers (there are 45 species of mosquito in Vermont, and he knows how to identify them all under a microscope). The sorted species are then sent to another lab, where they're tested for viruses. When the process is complete, Graham releases the results to the USGS disease map and to the Health Department.
Most sites don't have a light trap, because those are battery-powered and need to be set up the night before they're collected, and there are about 30 sites along the western corridor. Graham said he hopes to expand on that next year.
"That would totally depend on funding from the legislature," he said. "There's no way we can add people without funding."
While the state only has the resources to collect mosquitoes along the western corridor, Graham and Department of Health epidemiologist Erica Berl said they believe EEE exists in all 14 counties. That belief is based on a joint effort by the Department of Health and the federal Centers for Disease Control and Prevention (CDC) called the deer serum survey. Health department employees travel the state during deer season to big game reporting stations and take deer blood samples from the deer hunters bring in to report (hunters are required to report each kill at one of these stations around the state). The Department of Health sends the blood to CDC, where it is tested for EEE and Lyme Disease antibodies, among others.
Graham said the survey has found EEE antibodies in deer killed in every county in the state.
Because there's no human vaccine for EEE, Graham's team of four people is Vermont's first and last line of defense against EEE. Their testing allows health officials to identify where in Vermont people are especially at risk for the disease. The health department advises Vermonters to avoid time outside during dawn and dusk, wear mosquito repellant and long sleeves, and keep standing water away from their homes.
Inevitably, though, there will be mosquitoes. It's the job of Graham's team to find out just what those mosquitoes are carrying with them.
"It's been really interesting," Graham said of this summer's work. "We've learned a lot, and we're still trying to brainstorm how to be even more efficient in what we do. We know where some of our weaknesses are. I would've liked to get to more sites more frequently this year. That's hard to do."
