Abstract
BackgroundWild hosts are commonly co-infected with complex, genetically diverse, pathogen communities. Competition is expected between genetically or ecologically similar pathogen strains which may influence patterns of coexistence. However, there is little data on how specific strains of these diverse pathogen species interact within the host and how this impacts pathogen persistence in nature. Ticks are the most common disease vector in temperate regions with Borrelia burgdorferi, the causative agent of Lyme disease, being the most common vector-borne pathogen in North America. Borrelia burgdorferi is a pathogen of high public health concern and there is significant variation in infection phenotype between strains, which influences predictions of pathogen dynamics and spread.MethodsIn a laboratory experiment, we investigated whether two closely-related strains of B. burgdorferi (sensu stricto) showed similar transmission phenotypes, how the transmission of these strains changed when a host was infected with one strain, re-infected with the same strain, or co-infected with two strains. Ixodes scapularis, the black-legged tick, nymphs were used to sequentially infect laboratory-bred Peromyscus leucopus, white-footed mice, with one strain only, homologous infection with the same stain, or heterologous infection with both strains. We used the results of this laboratory experiment to simulate long-term persistence and maintenance of each strain in a simple simulation model.ResultsStrain LG734 was more competitive than BL206, showing no difference in transmission between the heterologous infection groups and single-infection controls, while strain BL206 transmission was significantly reduced when strain LG734 infected first. The results of the model show that this asymmetry in competition could lead to extinction of strain BL206 unless there was a tick-to-host transmission advantage to this less competitive strain.ConclusionsThis asymmetric competitive interaction suggests that strain identity and the biotic context of co-infection is important to predict strain dynamics and persistence.
Highlights
Wild hosts are commonly co-infected with complex, genetically diverse, pathogen communities
We introduced a parameter p to denote the probability of a mouse becoming infected with strain LG734 from a coinfected nymph; 1-p denoted the probability of infection with strain BL206
For the strains that infected second, strain BL206 transmission was significantly lower than the single-infection control (Wald = 22.89, P < 0.0001; Table 1 Post-hoc, Fig. 3), but there was no difference in transmission for strain LG734 compared to the single-infection control for that strain
Summary
Wild hosts are commonly co-infected with complex, genetically diverse, pathogen communities. Ticks are the most common disease vector in temperate regions with Borrelia burgdorferi, the causative agent of Lyme disease, being the most common vector-borne pathogen in North America. Ticks are the most common arthropod vector in temperate climates and Borrelia burgdorferi (sensu lato), the causative agent of Lyme disease, is the most prevalent vector-borne pathogen in these regions. Peromyscus leucopus, the white-footed mouse, is an integral part of the life-cycle of both I. scapularis and B. burgdorferi. These mice are the primary hosts of larval and nymphal tick stages, are highly competent hosts for the amplification of B. burgdorferi strains, and are abundant in the northeastern United States [11,12,13]. P. leucopus does not develop arthritic pathology, as seen in many laboratory mouse strains [14], suggesting significant differences in the physiological response to B. burgdorferi infection
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