Co-feeding transmission in Lyme disease pathogens

Abstract

This review examines the phenomenon of co-feeding transmission in tick-borne pathogens. This mode of transmission is critical for the epidemiology of several tick-borne viruses but its importance for Borrelia burgdorferi sensu lato, the causative agents of Lyme borreliosis, is still controversial. The molecular mechanisms and ecological factors that facilitate co-feeding transmission are therefore examined with particular emphasis on Borrelia pathogens. Comparison of climate, tick ecology and experimental infection work suggests that co-feeding transmission is more important in European than North American systems of Lyme borreliosis, which potentially explains why this topic has gained more traction in the former continent than the latter. While new theory shows that co-feeding transmission makes a modest contribution to Borrelia fitness, recent experimental work has revealed new ecological contexts where natural selection might favour co-feeding transmission. In particular, co-feeding transmission might confer a fitness advantage in the Darwinian competition among strains in mixed infections. Future studies should investigate the ecological conditions that favour the evolution of this fascinating mode of transmission in tick-borne pathogens.

Keywords: tick-borne pathogens.

Fig. 1.

The diagram shows (A) co-feeding (nymph-to-larva) transmission and (B) systemic (host-to-larva) transmission of Borrelia spirochaetes in a rodent reservoir host. Co-feeding transmission can occur when ticks feed in close spatial and temporal proximity on the same host. Larva 2 does not acquire spirochaetes via co-feeding transmission because it is too far away from the infected nymph. Systemic transmission occurs once the spirochaetes have had enough time to disseminate to all the relevant tissues of the reservoir host, which usually takes about 2 weeks. Under systemic transmission, larvae can acquire spirochaetes by attaching anywhere on the infected mouse.