Genomic insights into the ancient spread of Lyme disease across North America

Area of Science:

• Microbiology
• Evolutionary Biology
• Epidemiology

Background:

• Lyme disease is North America's most common tick-borne illness, with its bacterial origins and spread history remaining unclear.
• The causative agent, Borrelia burgdorferi sensu stricto (s.s.), was first identified in the 1970s.

Purpose of the Study:

• To investigate the evolutionary history and geographic spread of Borrelia burgdorferi s.s. in North America.
• To understand the factors contributing to the emergence of Lyme disease.

Main Methods:

• Collected ticks across the USA and southern Canada between 1984 and 2013.
• Sequenced 146 Borrelia burgdorferi s.s. genomes, representing the largest collection to date.
• Analyzed genomic data to reconstruct evolutionary history and migration patterns.

Main Results:

• Borrelia burgdorferi s.s. exhibits a complex evolutionary history with significant, previously unknown migration events.
• Bacterial diversity is ancient and widespread, predating the Lyme disease epidemic and the Last Glacial Maximum.
• No evidence suggests recent evolutionary changes in the bacterium driving Lyme disease emergence.

Conclusions:

• The emergence of human Lyme disease is likely linked to recent ecological shifts, including climate and land-use changes.
• The bacterium's evolutionary history is ancient and geographically extensive, independent of recent disease outbreaks.
• Understanding the bacterium's long-term history is crucial for predicting future Lyme disease dynamics.