Tom French, assistant director of the natural heritage and endangered species program of the Massachusetts Division of Fish and Wildlife, said researchers found bats infected with "white-nose syndrome" in Cheshire, Egremont and Sheffield.
On Friday, Vermont biologists reported sick bats just beyond the Williamstown border in Pownal, Vt.
The syndrome does not appear to infect humans or bats that live in places other than caves and abandoned mine shafts. The syndrome was named after a white fungus found on the noses of bats that appeared to have died from the disease. The syndrome appears to cause the bats to rapidly lose body fat and kills between 90 and 97 percent of an infected bat population.
"This has never happened before in this country or in the world, ever," French said on Friday. "To this day, we have no idea what's causing it."
While scientists probe bat corpses taken from caverns filled with decimated thousands, French said he was uncertain how the population drop would affect insect numbers this summer.
"Bats absolutely are a major controlling force of small, flying insects," he said. "Those insects can damage crops, gardens and our own health. But, it's still hard to say what the effect could be."
He said the number of cave-dwelling bats in Massachusetts is relatively small at about 12,000 because there are a limited amount of caves and mines. Counting the other species of bats that prefer to live in the attics of buildings is difficult, he said.
There are three species of bats in Massachusetts. Little brown bats tend to live in caves, large brown bats live in buildings and tree bats live more like birds, migrating to warmer climates during the winter.
French said scientists are trying to avoid spending much time in the infected caves and he would advise everyone else to do the same. Scientists are unsure whether human contact would introduce other harmful pathogens to bats with an already-weakened immune system.
"Several things scare me," he said. "Not only the question of 'Is it still spreading?' But, also, 'How long will it take to recover?' I think it's going to take decades."