Abstract:
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.
