Lyme Disease Bacteria Dates Back to the Ice Age

Lyme disease may feel like a modern epidemic—but the bacteria behind it is not new.

In an effort to understand the evolutionary history of Borrelia burgdorferi, Walter and colleagues at Yale University analyzed one of the largest collections of bacterial genomes assembled to date, using ticks collected across the United States and southern Canada between 1984 and 2013.

An Ancient and Widespread Pathogen

The researchers found that B. burgdorferi has a “complex evolutionary history with previously undocumented levels of migration.”

Importantly, the genetic diversity of the bacterium predates both the modern Lyme disease epidemic and even the Last Glacial Maximum approximately 20,000 years ago.

This suggests that Lyme disease bacteria have been present in North America since the Ice Age.

Why Lyme Disease Appears to Be Increasing

If the bacterium is ancient, why does Lyme disease appear to be a relatively recent and growing problem?

The authors point to ecological changes rather than bacterial evolution.

Changes in land use, deforestation, reforestation, expansion of white-tailed deer populations, and climate shifts have likely enabled the spread of ticks into new regions. For more on geographic expansion, see Lyme disease prevention.

The Role of Animal Hosts and Migration

Birds appear to play an important role in the spread of Lyme disease. The study found evidence of long-distance migration of ticks and bacteria between major geographic regions.

This bird-mediated dispersal helps explain how Lyme disease continues to expand across North America, including into southern Canada.

Genetic Diversity and Disease Severity

The researchers also found high levels of genetic diversity among B. burgdorferi strains.

Some strains are associated with more severe disease, and these strains are not confined to a single region.

“Disseminating strains associated with more severe disease are found in all regions surveyed,” the authors note.

Clinical Takeaway

Lyme disease is not a new infection—but its growing impact reflects environmental change, expanding tick habitats, and increased human exposure.

Patients may be exposed to diverse strains regardless of location, underscoring the importance of early recognition and prevention strategies.

References:

1. Walter KS, Carpi G, Caccone A, Diuk-Wasser MA. Genomic insights into the ancient spread of Lyme disease across North America. Nat Ecol Evol. 2017;1(10):1569-1576.

Dr. Daniel Cameron, MD, MPH
Lyme disease clinician with over 30 years of experience and past president of ILADS.

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