Lyme disease has European roots

More than 20,000 cases of Lyme disease, a bacterial infection transmitted by deer ticks, are diagnosed each year in the U.S. Researchers have speculated that Borrelia burgdorferi, the spirochete that causes the clinical symptoms of Lyme disease seen in this country, originated in North America. But a new study published in the June 24 issue of Proceedings of the National Academy of Sciences traces the bacterium’s pedigree to Europe.

Durland Fish, Ph.D., professor of epidemiology at the Yale School of Public Health, worked with an international team that analyzed 64 different samples of bacterial DNA from ticks and infected human patients in both the U.S. and Europe. By looking at mutations in a group of genes essential to basic metabolism, the scientists determined that European strains are more closely related to a common ancestor than are North American strains, indicating a European origin for the bacterium.

“Understanding the evolution of pathogens is a key epidemiological tool,” says Fish. “By understanding the evolutionary history of pathogens, we can better predict their evolutionary future.”