RAYNHAM — Aileen Griffith and her 17-year-old daughter, Leslie, picked the most punishing time of day to go power-walking.

Under a blaring noontime sun Saturday, with temperatures soaring into the 90s, they strode down one of the town’s main roads, wiping away sweat beading above their sunglasses.

It was far too toasty for their taste, but cooler walks at dawn or dusk are out of the question, they said.

The reason: Eastern equine encephalitis.

At sunset, “the mosquitoes are wicked bad around here,” said Leslie.

“It’s too much of a risk to go out in the evening,” said Aileen.

This year, reports of mammal-biting mosquitoes carrying Eastern equine encephalitis have come earlier than anyone could remember: On Wednesday, the Massachusetts Department of Public Health announced that mosquitoes collected earlier in the week in Easton were found to be carrying the virus. On Thursday, another sample from Carver came back positive.

State officials have listed Easton, Raynham, and Taunton as being at high risk for the virus, and residents in Southeastern Massachusetts are on edge as they reschedule evening activities, double up on bug spray, and clamor for town and state officials to spray their neighborhoods.

Their fears are not unfounded: Last year, 80-year-old Martin Newfield of Raynham died less than two weeks after contracting the virus.

Catherine Brown, the state public health veterinarian, explained that two types of mosquitoes carry the virus. The species that bites birds is often discovered carrying the virus early in the summer, she said. But the kind that targets mammals, including humans, is not typically found with the virus until about July 25.

The discovery of mammal-biting insects carrying the virus in the second week of July, she said, is a cause for concern.

Anthony Texeira, superintendent of the Plymouth County Mosquito Control Project, agreed that the early onset was worrisome.