Cellular and immunological mechanisms influence host-adapted phenotypes in a vector-borne microparasite

Area of Science:

• Evolutionary biology
• Microbiology
• Disease ecology

Background:

• Pathogen host range and competence are key to predicting emergence and spillover.
• Host competence is often viewed as fixed but can vary with pathogen diversification.
• Multiple-niche polymorphism (MNP) can maintain pathogen diversity under balancing selection.

Purpose of the Study:

• Investigate mechanisms of Borrelia burgdorferi (Bb) strain adaptation to different hosts.
• Determine if Bb strains with specific outer surface protein C (ospC) genotypes exhibit host-dependent adaptation.
• Explore the role of MNP in maintaining Bb diversity.

Main Methods:

• Infection of American robins and white-footed mice with three Bb strains of different ospC genotypes.
• Quantification of Bb burdens and assessment of strain persistence within hosts.
• Evaluation of early survival phenotypes, including cell adhesion and immune evasion.

Main Results:

• Bb burdens varied significantly by strain in a host-dependent manner.
• Strain persistence correlated with early survival and transmission to tick larvae (fitness).
• Early survival was linked to cell adhesion, complement evasion, and immune responses, suggesting selective pressures.

Conclusions:

• Bb strains exhibit differential adaptation to hosts, supporting host-specific selection.
• MNP may play a crucial role in maintaining ospC diversity in Bb.
• Findings inform eco-evolutionary models for microparasite host adaptation.