ALBANY — The black-legged ticks whose bites cause Lyme disease are expected to be out in abundance in much of the Northeast this year, says a researcher whose forecast is based on the boom-bust forest population of white-footed mice.

And it all has to do with acorns.

Richard Ostfeld, a disease ecologist at the Cary Institute of Ecosystem Studies in Millbrook, said oak trees left a bumper crop of acorns on the forest floor in 2015, contributing to a surge in the population of mice in 2016.

The mice, many of them infected with Lyme disease, are the main hosts for the tick nymphs that will be re-emerging in coming weeks, he said in an interview from his research center in New York’s Hudson Valley.

“They will be super-hungry because they haven’t eaten in a long time,” said Ostfeld, explaining the nymphs, after transforming from larval stage last year, “entered a state of suspended animation” for the winter months.

Ostfeld and his fellow researchers have been monitoring mice and other rodents since the early 1990s. Each summer, he explained, they use metal traps to live-capture mice, with the goal of gauging their population trends.

“It’s sort of like conducting a census, though it’s all done in the same zip code,” he said. “We kind of go door-to-door where the mice live.”

The mice are tagged, though not all of the ones that wind up in traps had been previously marked. The difference in the number of tagged mice and untagged ones in the traps provides an indication as to where the overall population is heading.

“The fact that we have been doing this for a very long time gives us a reasonable level of confidence in our predictions,” he said.

Some mammals will try to whisk off the ticks. But not mice — even with scores of ticks trying to use them as hosts for a blood snack, Ostfeld said.

“They just seem to shrug it off,” he said.

The tick nymphs that will be re-emerging this spring, Ostfeld said, will be “at a dangerous stage” because of their voracious appetite.

He also predicted that while May has been designated Lyme Disease Month to raise public awareness about the need to take preventive measures, the risk will become great in April as the result of a relatively mild winter.

“There were hordes of mice during the summer of 2016, and so now we’re expecting a lot of infected nymphs of the black-legged tick this coming spring and early summer,” Ostfeld said.

The Centers for Disease Control and Prevention says Lyme disease is the most commonly reported vectorborne illness in the nation, with 95 percent of reported cases coming from the Northeast and upper Midwest. The number of cases in the two regions doubled from 2001 to 2015, according to the federal agency.

Getting infected with the bacteria that causes Lyme can produce a red rash, fatigue, fever, headaches, swelling and joint pain.

Because the ticks can be difficult to spot, health experts recommend that people don light clothing before heading into woods and fields. Using insect repellant and inspecting one’s own body and pets for ticks are also recommended. No vaccines have been developed to protect against the bacteria.

Researchers at the Cary Institute have found that one of the best allies in countering ticks is the opossum. Ostfeld said the mammal, unlike mice, are meticulous groomers who gobble up the ticks, thus leaving fewer available to target potential human hosts.

It is also likely, he said, that raptors help in countering Lyme, as they are known to dine on mice, though the challenge in studying the phenomenon has left researchers with insufficient data to make any firm conclusions.

The best news from the recent research, he said, is that the acorn drop decreased in 2017, which should lead to fewer mice this year and an expected decline in black-legged ticks in 2018.

But ticks are expected to be an ongoing problem, he said, noting climate change is already increasing the risks posed by the blood-sucking insects.

Ostfeld has also postulated that environmental changes from habitat fragmentation increases disease risk by reducing predators and biodiversity.

Joe Mahoney covers the New York Statehouse for CNHI’s newspapers and websites. Reach him at jmahoney@cnhi.com

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