Lyme Bacterium, Once Nearly Eradicated In U.S., Rebounded With Forests

In post-colonial America, Lyme disease was isolated to a few islands along the Northeast coast and pockets of Wisconsin and Minnesota. But a new genetic analysis of the Lyme bacterium by Yale researchers shows that the tick-borne disease roared back after the reforestation of this part of the country.

The findings, reported the week of August 10 in the Proceedings of the National Academy of Sciences, show Lyme spread from the Northeast to the Midwest thousands of years ago. Deforestation eliminated the deer that host Lyme-carrying ticks and the range of the disease was dramatically decreased.

“The current epidemic of Lyme disease is the result of infected ticks expanding their range independently from these isolated refuges,” said Durland Fish, professor of epidemiology at the Yale School of Public Health 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.”

Researchers collected samples of the Lyme bacterium Borrelia burgdorferi from black-legged ticks throughout its range in the eastern half of the country. Researchers analyzed mutations in the genome of the bacterium that allowed them to trace the evolutionary path it took in the U.S. They found ancestral variations in genetic sequences of bacterium that suggest it originated in the Northeast U.S. and then spread to the Midwest. Previous analysis of the bacterium suggests it first originated in Europe.

“An understanding of how and why Lyme disease is spreading has important public health applications,” Fish said.

The University of California at Irvine and the University of Bath contributed to the study. Former Yale doctoral student, Anne Gatewood Hoen, now at Harvard, was lead author of the paper. Other Yale authors include Maria Diuk-Wasser and Stephen Bent at the Yale School of Public Health.

The study was funded by the National Institutes of Health, the Centers for Disease Control, the U.S. Department of Agriculture and the Mathers Foundation.