Written by: Michaeleen Doucleff and Jane Greenhalgh
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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.
How Lyme Disease Cases Have Spread In The U.S.
The number of confirmed and probable Lyme disease cases in the U.S. more than doubled from 2001 to 2015. In 2015, 95 percent of confirmed cases were reported in the 14 states labeled below.
Because data are reported on the county level, the CDC randomly placed a dot within the county of residence for each case.