Dynamics Of Pathogen Co-Infection And Rickettsia Endosymbionts In Ixodes Scapularis (acari: Ixodidae) In Connecticut

Darya Pokutnaya

Revised thesis published in 2020. Please see the PubMed record: https://www.ncbi.nlm.nih.gov/pubmed/31971489


Introduction: Ixodes scapularis or blacklegged tick transmits at least seven pathogens including Anaplasma phagocytophilum, Babesia microti, Borrelia burgdorferi, and Borrelia miyamotoi to humans. Ixodes scapularis can also be colonized by symbiotic bacteria including those in the spotted fever group of the genus Rickettsia. Improved understanding of the status of pathogen infection(s) in I. scapularis is important for evaluating the risk of tick-borne diseases.

Objectives: The objectives of this study were to estimate the prevalence of infection with A. phagocytophilum, B. microti, B. burgdorferi, and B. miyamotoi in I. scapularis, to determine the status of Rickettsial endosymbiont activity in Connecticut, and to evaluate whether prevalence of co-infection occurs at the same frequency that would be expected based on single infections.

Methods: We used PCR and pathogen-specific primers to test 460 I. scapularis for the prevalence of infection and Rickettsia spp. activity. The sample was chosen such that half were positive for B. burgdorferi and half were either nymphs or females to determine the relationship between each pathogen with B. burgdorferi.

Results: The prevalence of B. burgdorferi was highest among mono-infections with 47% of ticks infected, followed by B. miyamotoi (7.8%), A. phagocytophilum (5.7%), and B. microti (5.2%). Sequence analyses indicated no evidence of pathogenic Rickettsia spp.; however, 93.0% of ticks were colonized with endosymbiotic Rickettsia. Nymphs were more likely to be infected with B. burgdorferi if they were infected with B. microti (OR = 7.08; 95% CI: 1.53, 32.71). Females were more likely to be infected with B. burgdorferi if they were infected with A. phagocytophilum (OR = 7.40; 95% CI: 1.62, 33.89) or B. miyamotoi (OR = 2.46; 95% CI: 1.12, 5.44).

Conclusion: Our findings indicate differences in pathogen prevalence across the CT counties. Furthermore, our results suggest that the prevalence of B. burgdorferi is not independent from the status of other pathogens co-circulating in I. scapularis. Our results indicate a higher prevalence of B. miyamotoi in I. scapularis females collected.