Erica Berl isn’t a hunter, but she got up early on Saturday and bundled up for a long morning outside waiting for deer.
Berl’s hunt came after the deer hunters, out for Vermont’s annual youth hunting weekend, finished theirs. After pairs of hunters – children with their older siblings, a parent or a family friend – heaved deer onto the scale at the Department of Fish and Wildlife reporting station in Swanton, Berl and her team got to work.
In Swanton and at 22 other locations across Vermont, the Department of Health was piggybacking Saturday on the reporting requirements for hunting season in its continuing effort to track Eastern Equine Encephalitis (EEE) across the state.
“Wherever EEE occurs, it tends to cause human illness in very focal areas, so it can be helpful to know where it’s circulating and where there’s enough of it that we think there’s a risk to human or mammalian illness, especially horses,” Berl said.
The teams collected blood samples from deer killed and asked hunters to point out on a map where they shot the deer. The state sends the blood samples to the Centers for Disease Control and Prevention, where they’re tested for antibodies to EEE.
Unlike humans, who can become severely ill and – in about 35 percent of cases – die from EEE, deer form antibodies as an immune response when they’re exposed, and do so without getting seriously sick. The antibodies stay in their system for months or years, Berl said, so they become walking evidence of EEE’s presence in Vermont.
The Health Department has been testing deer blood since the 2010 hunting season, when it collected 489 samples and found that about 10 percent of them tested positive for EEE antibodies. It was the first evidence of the virus in the state, and it was widespread; deer that tested positive came from 12 of Vermont’s 14 counties.
Since then, the rate of exposure in the deer blood samples collected has held fairly steady, but the disease has also spread to humans and domestic animals. This year, two horses in Franklin County died as a result of contracting EEE. Two Vermont men died in 2012 from the virus.
There is no human vaccine for EEE, so Berl’s efforts paired with Vermont’s four-person mosquito surveillance team are the only thing between Vermonters and the severe illness that comes from being bit by an infected mosquito.
“Being forewarned about a possible illness, I think, will enhance people’s use of personal protection measures,” Berl said, such as wearing long-sleeved shirts, using repellent and staying inside.
Berl said her hope is that better knowledge of where EEE is most prevalent will help the Department of Health target its messaging efforts. But the deer serum survey is also the state’s way of turning hunters into what is essentially a massive statewide data collection force that will help steer a smaller, more geographically focused force.
When the much smaller mosquito surveillance team headed by state entomologist Alan Graham resumes their work capturing and testing mosquitoes next spring, they will use the deer serum data to carefully select the small swaths of land they’re able to cover.
“If we do see some clustering positivity near some wetlands,” Berl said, “we may decide to then do increased mosquito surveillance in those areas. Because we can’t do mosquito surveillance everywhere, we just don’t have the resources.”
But if there are no clusters, “then it actually raises more questions than we have answers for,” Berl said.
Whatever the outcome, she said, “it’s all very interesting.”
