Cross-Immunity and Community Structure of a Multiple-Strain Pathogen in the Tick Vector

Area of Science:

• Microbiology and Infectious Diseases
• Vector-borne Pathogen Ecology
• Genetics and Evolutionary Biology

Background:

• Vector-borne pathogens often comprise multiple strains circulating between hosts and vectors.
• Understanding pathogen strain communities in vectors is crucial for mixed infection epidemiology.
• Borrelia afzelii and Borrelia garinii cause Lyme disease, utilizing the Ixodes ricinus tick but differing in vertebrate host adaptation.

Purpose of the Study:

• To investigate the impact of vertebrate cross-immunity on the structure of Borrelia ospC (outer surface protein C) strain communities in Ixodes ricinus ticks.
• To characterize the diversity and origin of ospC alleles within Borrelia afzelii and Borrelia garinii tick isolates.

Main Methods:

• Culturing Borrelia isolates from field-collected Ixodes ricinus ticks over 11 years.
• Species identification using reverse line blot (RLB) assay.
• Deep sequencing to analyze ospC gene communities in 190 B. afzelii and 193 B. garinii isolates.

Main Results:

• Mixed ospC strain infections were common in ticks.
• Vertebrate cross-immunity did not significantly influence the Borrelia strain structure within the tick vector.
• Over 50% of isolates contained exotic ospC alleles, suggesting potential cryptic coinfections or horizontal gene transfer.

Conclusions:

• Vertebrate cross-immunity does not appear to structure Borrelia strain communities in the tick vector.
• Genetic variation at the ospC locus indicates selection against intermediately divergent alleles.
• The prevalence of exotic ospC alleles warrants further investigation into coinfection dynamics and horizontal gene transfer in Borrelia.