Host adaptation drives genetic diversity in a vector-borne disease system

Area of Science:

• Microbiology
• Ecology
• Epidemiology

Background:

• Borrelia burgdorferi sensu stricto (Bb) causes Lyme disease and is considered a generalist pathogen infecting mammals and birds.
• Understanding the variation in Bb's host range is crucial for assessing human disease risk and pathogen transmission dynamics.
• Intraspecific variation in Bb host breadth and its impact on host competence remain poorly understood.

Purpose of the Study:

• To investigate the extent of intraspecific variation in Bb host breadth.
• To determine the role of Bb genotype diversity in host competence and adaptation.
• To explore the implications of Bb host adaptation for human Lyme disease risk.

Main Methods:

• Long-term study of Bb diversity using the polymorphic ospC locus.
• Long-read amplicon sequencing of Bb from white-footed mice, passerine birds, and tick vectors.
• Analysis of genotype-specific host adaptation and persistence.

Main Results:

• Significant variation in host breadth was observed across different Bb genotypes, revealing genotype-specific host-adapted phenotypes.
• Passerine birds support the circulation of human-invasive strains (HISs) and harbor greater Bb genotypic diversity than mice.
• Mouse-adapted Bb genotypes showed longer persistence in mice, with infecting communities becoming dominated by these adapted genotypes over time.

Conclusions:

• Intraspecific variation in Bb host breadth and adaptation is a key factor maintaining pathogen diversity and fitness.
• Multiple niche polymorphism contributes to Bb diversity, with limited evidence of strong frequency-dependent selection.
• Understanding genotype-specific host adaptation is essential for predicting Lyme disease risk and managing pathogen reservoirs.