In mid-September, Meghan Siegal’s Sherborn soccer club sent an email to all volunteer coaches, including herself, that said practices must now end at 6 p.m. sharp. The reason: to avoid the twilight hours when mosquitoes that carry the virus Eastern equine encephalitis are most active.

State officials have placed Sherborn, and 39 other cities and towns, at high risk for EEE. Another 35 have been listed at critical, the highest risk level. Residents are being urged to follow health department recommendations that include rescheduling outdoor events to avoid dusk-to-dawn hours and wearing mosquito repellent when spending time outside.

Siegal says it’s the first time she can remember an alert for the virus in the decade she’s lived in the area. Unlike residents in Massachusetts’ traditional hotspots for EEE, Bristol and Plymouth counties, those around Sherborn aren't accustomed to hearing warnings about EEE.

A horse leaves a barn at Willow Brook Farms in Holliston, Mass. Last month, a horse here named Bruin contracted EEE and passed away. (Angus Chen/WBUR)

But this year the virus is more widespread, says state epidemiologist Catherine Brown, and many communities are facing elevated EEE risk for the first time in decades. Already, health officials have confirmed 10 human infections, two of them fatal.

“This year, we’re seeing cases in almost all the places that have ever seen EEE activity. So that for us is unusual,” Brown says. “[We’re] working with communities dealing with it for the first time. That’s been very challenging.”

While communities in Bristol and Plymouth counties responded quickly and easily to health department guidelines for high or critical EEE risk – meaning EEE has been detected in mosquitoes, and there has been a human or animal case in the area – it’s been more difficult for towns and cities not used to the virus, Brown says.

“Some of those areas don’t have access to mosquito control project services, so mosquito surveillance is less robust, or they don’t have easy access to [mosquito control] spraying,” Brown says. “And these communities and residents have less experience dealing with this. It’s disrupting after-school sports schedules and things like that. If you’re not used to doing that, doing it for the first time takes some thought and adjustment.”

It can be complicated to know when to cancel outdoor events, for example, something that Siegal now grapples with regularly. She says she weighs the day’s humidity, wind speeds and temperature when deciding whether or not to run her daughter’s 4th grade soccer practice.

“It’s a decision that I think about, you know, two or three times a week, and it’s a lot,” she says.

In the last couple of decades, EEE has become more widespread throughout the Northeast, according to Brown. “Historically, Massachusetts has by far the most EEE activity. But Vermont, New Hampshire and Maine have only had EEE in the last 15 years or so. It had never been identified there before," she says. “It’s easy to say this could be a potential impact of climate change.”

This year has been particularly bad, with seven deaths occurring in Massachusetts, Michigan, Connecticut and Rhode Island combined. There have been at least 26 human infections from the virus identified across the country.

EEE infects the central nervous system and can cause severe brain damage. Epidemiologists estimate that it results in death roughly 40% of the time.

Brown says outbreaks are usually triggered by a combination of two things: a new strain of the virus being introduced to the region from Florida and wetter-than-usual conditions over the last year. She thinks these factors may explain the elevated activity the state is experiencing this year.

“Having a new strain of the virus from Florida tends to kick off a new [EEE] cycle. I can’t prove it yet, but I anticipate that we are going to discover this is a newly introduced viral strain,” she says. “And there was a lot of rain last fall and this spring. That means you will have larger mosquito populations.”

But Brown stresses that EEE is still a very rare disease. “Most people do not get EEE. We tested over 400 people this season who had symptoms like EEE but didn’t have it,” she says. “Just because you have a mosquito bite does not mean you are going to get EEE necessarily and, in fact, you’re unlikely to get it."

Plus, the likelihood of contracting EEE is waning as winter approaches, Brown says.

“As temperatures get below 50, it’s unlikely there will be mosquitoes out,” she says. “But people should still follow recommendations about using mosquito repellent and avoiding those dusk-to-dawn hours until a hard frost.”