Prevalence of Borrelia burgdorferi and diversity of its outer surface protein C (ospC) alleles in black-legged ticks (Ixodes scapularis) in Delaware

Authors: SCHIFFLETT, SCARLETT - University Of Delaware; WIEDMEYER, TYLER - University Of Delaware; KENNEDY, ASHLEY - State Of Delaware Division Of Fish & Wildlife; Maestas, Lauren; BUONI, MICHAEL - Delaware Biotechnology Institute; CILOGLU, ARIF - Erciyes University; ELLIS, VINCENZO - University Of Delaware

Submitted to: Ticks and Tick Borne Diseases
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/3/2023
Publication Date: 2/11/2023
Citation: Schifflett, S.A., Wiedmeyer, T., Kennedy, A., Maestas, L.P., Buoni, M., Ciloglu, A., Ellis, V.A. 2023. Prevalence of Borrelia burgdorferi and diversity of its outer surface protein C (ospC) alleles in black-legged ticks (Ixodes scapularis) in Delaware. Ticks and Tick Borne Diseases. https://doi.org/10.1016/j.ttbdis.2023.102139.
DOI: https://doi.org/10.1016/j.ttbdis.2023.102139

Interpretive Summary: Understanding the diversity of genes associated with virulence and transmission of a pathogen across its range can improve our understanding of host infection risk. Borellia burgdorferi is a bacterial agent of Lyme disease in humans and is the most common vector-borne infectious disease in the United States. The outer surface protein C (ospC) gene of B. burgdorferi exhibits high genetic variation across the pathogen’s distribution and plays a critical role in virulence and transmission in vertebrate hosts. In fact, disseminated B. burgdorferi infections in humans is associated with only a subset of circulating ospC alleles. The state of Delaware has a high incidence of Lyme disease, but the diversity of ospC in B. burgdorferi in the state has not been evaluated. We used PCR to amplify ospC in B. burgdorferi - infected black-legged ticks (Ixodes scapularis) in sites across Delaware’s three counties and used short-read sequencing to identify ospC alleles. B. burgdorferi prevalence in black-legged ticks varied across sites, but not significantly so. We identified 15 previously characterized ospC gene accounting for nearly all expected diversity of genes across the sites as estimated using the Chao1 index. Nearly 40% of sequenced infections (23/58) had more than one ospC allele present suggesting mixed strain infections) and the relative frequencies of alleles in single infections was positively correlated with their relative frequencies in mixed infections. Turnover of ospC gene variation was positively related to distance between sites with closer sites having more similar gene compositions than more distant sites, suggesting a degree of dispersal limitation. OspC alleles known to cause disseminated infections in humans were found at the highest frequencies across sites, corresponding to Delaware’s high case rate of Lyme disease.

Technical Abstract: Quantifying the diversity of genes associated with virulence and transmission of a pathogen across its distribution can inform our understanding of host infection risk. Borellia burgdorferi is a bacterial agent of Lyme disease in humans and is the most common vector-borne infectious disease in the United States. The outer surface protein C (ospC) gene of B. burgdorferi exhibits high geneticvariation across the pathogen’s distribution and plays a critical role in virulence and transmission in vertebrate hosts. In fact, disseminated B. burgdorferi infections in humans is associated with only a subset of circulating ospC alleles. The state of Delaware has a high incidence of Lyme disease, but the diversity of ospC in B. burgdorferi in the state has not been evaluated. We used PCR to amplify ospC in B. burgdorferi - infected black-legged ticks (Ixodes scapularis) in sites across Delaware’s three counties and used short-read sequencing to identify ospC alleles. B. burgdorferi prevalence in black-legged ticks varied across sites, but not significantly so. We identified 15 previously characterized ospC alleles accounting for nearly all expected diversity of alleles across the sites as estimated using the Chao1 index. Nearly 40% of sequenced infections (23/58) had more than one ospC allele present (suggesting mixed strain infections) and the relative frequencies of alleles in single infections was positively correlated with their relative frequencies in mixed infections. Turnover of ospC alleles was positively related to distance between sites with closer sites having more similar allele compositions than more distant sites, suggesting a degree of dispersal limitation. OspC alleles known to cause disseminated infections in humans were found at the highest frequencies across sites, corresponding to Delaware’s high incidence of Lyme disease.