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
analysis indicates 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.