Ecological interactions driving population dynamics of two tick-borne pathogens, Borrelia burgdorferi and Babesia microti

Borrelia burgdorferi (Bb) and Babesia microti (Bm) are vector-borne zoonotic pathogens commonly found co-circulating in Ixodes scapularis and Peromyscus leucopus populations. The restricted distribution and lower prevalence of Bm has been historically attributed to lower host-to-tick transmission efficiency and limited host ranges. We hypothesized that prevalence patterns are driven by coinfection dynamics and vertical transmission. We use a multi-year, multiple location, longitudinal dataset with mathematical modelling to elucidate coinfection dynamics between Bb and Bm in natural populations of P. leucopus, the most competent reservoir host for both pathogens in the eastern USA. Our analyses indicate that, in the absence of vertical transmission, Bb is viable at lower tick numbers than Bm. However, with vertical transmission, Bm is viable at lower tick numbers than Bb. Vertical transmission has a particularly strong effect on Bm prevalence early in the active season while coinfection has an increasing role during the nymphal peak. Our analyses indicate that coinfection processes, such as facilitation of Bm infection by Bb, have relatively little influence on the persistence of either parasite. We suggest future work examines the sensitivity of Bm vertical transmission and other key processes to local environmental conditions to inform surveillance and control of tick-borne pathogens.

Automated summary

This study used a multi-year, multiple location, longitudinal dataset and mathematical modeling to investigate the coinfection dynamics between Bb and Bm in natural populations of P. leucopus in the eastern USA. The results showed that Bb can survive at lower tick numbers without vertical transmission, while Bm requires more ticks. However, with vertical transmission, Bm can survive at lower tick numbers. Vertical transmission has a strong impact on Bm prevalence early in the active season, while coinfection plays a larger role during the nymphal peak. Future research should examine the sensitivity of Bm vertical transmission and other key processes to local environmental conditions to guide tick-borne pathogen surveillance and control.