Scientist says lack of acorns may mean more Lyme disease in Maine

Posted April 07, 2012, at 5:38 a.m.
The white-footed mouse is the preferred host of black-legged ticks, which carry Lyme disease.
The white-footed mouse is the preferred host of black-legged ticks, which carry Lyme disease.

RUMFORD, Maine — Conditions are ripe this year in the Northeast for a surge in Lyme disease and the black-legged ticks that carry it.

But disease specialists differ somewhat on the reason.

Maine state epidemiologist Stephen Sears attributed the predicted increase, at least in Maine, to the mild winter, the life cycle of ticks and the deer and white-footed mice that carry the disease.

However, disease ecologist Richard Ostfeld of the Cary Institute of Ecosystem Studies in Millbrook, N.Y., mostly bases the impending surge on fluctuations in acorns and populations of white-footed mice.

Ostfeld said acorn crops vary from year to year, with cycles that influence the winter survival and breeding success of white-footed mice.

White-footed mice transmit Borrelia burgdorferi, the bacterium that causes Lyme disease which if left untreated can cause arthritis, chronic fatigue and neurological problems.

“We had a boom in acorns, followed by a boom in mice, and now, on the heels of one of the smallest acorn crops we’ve ever seen, the mouse population is crashing,” Ostfeld said.

“This spring, there will be a lot of Borrelia burgdorferi-infected black-legged ticks in our forests looking for a blood meal, and instead of finding a white-footed mouse, they are going to find other mammals — like us,” he said.

Last year, Maine had 998 cases of Lyme disease and cases were found in every county, Sears said. This year, he believes it will go even higher.

“What we know is that Lyme disease is pretty much throughout the state of Maine and we’re seeing really significant amounts every year,” he said.

For more than two decades, Ostfeld and other Cary Institute ecologists and researchers have investigated connections among acorn abundance, white-footed mice, black-legged ticks and Lyme disease.

They conducted studies in central Dutchess County, N.Y., a fairly rural area, Ostfeld said.

He said that in 2010, that county experienced its heaviest record of acorns, and the mouse population followed suit in 2011, peaking in the summer months.

“The scarcity of acorns in the fall of 2011 set up a perfect storm for human Lyme disease risk,” Ostfeld said.

Their predictions, he said, should pertain to anywhere oaks are an important component of the forest and where they produced a heavy acorn crop in 2010.

“We know this acorn boom was quite widespread in the Northeast and Mid-Atlantic region, but we don’t know about Maine specifically,” he said.

The life cycle of black-legged ticks takes two years to go from larva to adult. Sears said it’s the adult that goes to deer, while the larvae and nymphs go to mice.

“And it’s the nymph that we tend to think carries more of the Lyme organism,” he said. “All of them can, but that’s the one we see more in the summertime.”

Ostfeld agreed.

“While adult ticks can transmit Lyme, they are responsible for a small fraction of tick-borne disease, with spring-summer nymphs posing more of a human health threat,” he said.

Sears said Ostfeld’s mice and acorns theory has merit.

“We’ve got lots of mice, we’ve got lots of deer, we’ve got lots of ticks and all those things come together to give us a pretty significant amount of Lyme disease,” Sears said.

“It’s here and we need to make sure people know as much as they can about it, because they need to be their own best advocates.”

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