Genetic footprints on the trail of Lyme disease

In post-Colonial America, settlers’ need for fuel, building materials, and tillable land led to unprecedented deforestation. Between 1830 and 1880, nearly 80 percent of New England’s forests disappeared.

A genetic analysis of the bacterium that causes Lyme disease, reported by School of Medicine scientists in the August 14 online issue of Proceedings of the National Academy of Sciences, suggests that the disease, which is transmitted by deer ticks, largely disappeared from New England along with the trees, but roared back when the region was reforested and deer returned.

Samples of the Lyme disease bacterium Borrelia burgdorferi from ticks in the Midwest and Northeastern U.S. showed genetic variations that suggest the disease was widespread for thousands of years but retreated to pockets of the northern Midwest and isolated islands off the New England coast after deforestation.

“The current epidemic of Lyme disease is the result of infected ticks expanding their range independently from these isolated refuges,” says Durland Fish, Ph.D., professor of epidemiology and senior author of the paper. “This expansion is likely to continue until the ticks, and the diseases they carry, return to their former range.”