Unveiling the Influence of Host Adaptation: Genetic Diversity in Lyme Disease Bacteria

 A research study delves into the underlying mechanisms of genetic diversity within the bacteria responsible for Lyme disease. Lyme disease stands as the most prevalent vector-transmitted illness in the United States, with approximately 476,000 human cases recorded each year. The primary culprit behind Lyme disease is the bacterium Borrelia burgdorferi (Bb), transmitted through ticks and capable of infecting a broad spectrum of mammals and avian species.

Led by Matthew Combs and his team, the study specifically investigates the genetic variation of Bb, focusing on the outer surface protein C (ospC) gene—a well-recognized virulence factor crucial for the pathogen's survival within ticks and during the initial stages of vertebrate infection. The findings are detailed in the PNAS Nexus journal.

Employing an extensive long-read high-throughput sequencing technique, the researchers examined a highly polymorphic locus in samples extracted from 553 white-footed mice, 92 passerine birds spanning 11 species, and 628 tick nymphs. These specimens were collected on Block Island, Rhode Island, between the years 2013 and 2020.

The results unveiled a diverse range of genotypes, yet the dominance of specific variants remained consistent over time, contrary to the anticipated shift driven by negative frequency-dependent selection. Instead, the observed genotypic variations exhibited correlations with distinct host species, indicating that ospC demonstrates host-specific variability intertwined with robust immunological connections.

Reinforcing the hypothesis of multiple niche polymorphism, genotypes adapted to mice were more likely to persist within mouse hosts compared to other genotypes. The outcomes bolster the concept that pathogens tailor their adaptations to animal hosts on a variant level. Consequently, the research suggests the necessity for a more nuanced definition of "host competence," incorporating a comprehensive comprehension of pathogen diversity, as emphasized by the study's authors.