Forbidding Forecast For Lyme Disease In The Northeast

Posted on May 16, 2017 in Chronic Disease, Medical Rewind

White-footed mice are efficient transmitters of Lyme disease in the Northeast. They infect up to 95 percent of the ticks that feed on them. But it’s people who create the conditions for Lyme outbreaks by building homes in the animals’ habitat. [Stephen Reiss for NPR]

Last summer Felicia Keesing returned from a long trip and found that her home in upstate New York had been subjected to an invasion.

“There was evidence of mice everywhere. They had completely taken over,” says Keesing, an ecologist at Bard College.

It was a plague of mice. And it had landed right in Keesing’s kitchen.

“Not only were there mouse droppings on our countertops, but we also found dead mice on the kitchen floor,” says Keesing’s husband, Rick Ostfeld, an ecologist at the Cary Institute of Ecosystem Studies in Millbrook, N.Y.

The Hudson River Valley experienced a mouse plague during the summer of 2016. The critters were everywhere. For most people, it was just a nuisance. But for Keesing and Ostfeld, the mouse plague signaled something foreboding.

“We’re anticipating 2017 to be a particularly risky year for Lyme,” Ostfeld says.

Keesing and Ostfeld, who have studied Lyme for more than 20 years, have come up with an early warning system for the disease. They can predict how many cases there will be a year in advance by looking at one key measurement: Count the mice the year before.

The number of critters scampering around the forest in the summer correlates to the Lyme cases the following summer, they’ve reported.

The explanation is simple: Mice are highly efficient transmitters of Lyme. They infect up to 95 percent of ticks that feed on them. Mice are responsible for infecting the majority of ticks carrying Lyme in the Northeast. And ticks love mice. “An individual mouse might have 50, 60, even 100 ticks covering its ears and face,” Ostfeld says.

So that mouse plague last year means there is going to be a Lyme plague this year. “Yep. I’m sorry to say that’s the scenario we’re expecting,” Ostfeld says.

Mice and ticks get along swimmingly. Other animals, such as possums, groom away ticks — and sometimes kill them. But white-footed mice tolerate ticks covering their faces and ears. Blacklegged ticks, like the adult female on the right, are tiny — about the size of a sesame seed.

Stephen Reiss for NPR

He’s not exactly sure which parts of the Northeast will be at highest risk.

But wherever Lyme exists, people should be vigilant, says epidemiologist Kiersten Kugeler at the Centers for Disease Control and Prevention.

“Whether it’s a bad season or not, there’s still going to be a lot of human cases of tick-borne diseases,” she says. “What’s important for people to know is that the ticks are spreading to new areas — and tick-borne diseases are coming with them.”

Back in the early ’80s, the disease wasn’t that big a problem. Cases were confined to two small regions: western Wisconsin and the area from Connecticut to New Jersey.

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