Experimental parasite community perturbation reveals associations between Sin Nombre virus and gastrointestinal nematodes in a rodent reservoir host.

Amy R Sweeny,Courtney A Thomason,Amy B Pedersen,Edwin A Carbajal,Christina B Hansen,Andrea L Graham

doi:10.1098/rsbl.2020.0604

Abstract

Individuals are often co-infected with several parasite species, yet measuring within-host interactions remains difficult in the wild. Consequently, the impacts of such interactions on host fitness and epidemiology are often unknown. We used anthelmintic drugs to experimentally reduce nematode infection and measured the effects on both nematodes and the important zoonosis Sin Nombre virus (SNV) in its primary reservoir (Peromyscus spp.). Treatment significantly reduced nematode infection, but increased SNV seroprevalence. Furthermore, mice that were co-infected with both nematodes and SNV were in better condition and survived up to four times longer than uninfected or singly infected mice. These results highlight the importance of investigating multiple parasites for understanding interindividual variation and epidemiological dynamics in reservoir populations with zoonotic transmission potential.

Highlights

Co-infection with both microparasites and macroparasites is common in the wild [1,2]
There were no significant predictors of nematode infection probability at first capture, and only time of season was a significant predictor of nematode infection intensity (Julian date: β = 0.90, s.e. = 0.26, p < 0.001), where EPG increased throughout the summer
Efforts to understand the risk of emerging infectious disease from wildlife reservoirs commonly focus on anthropogenic or environmental factors that influence contact at the human–wildlife interface [35,36,37], while interindividual variation in susceptibility and transmission potential within reservoir hosts remains under-studied [38,39]

Summary

Introduction

Co-infection with both microparasites and macroparasites is common in the wild [1,2]. Interactions among parasites co-habiting a host can occur through multiple mechanisms, including bottom-up (e.g. resource competition) or top-down (e.g. immune-mediated) processes [3,4,5]. Removal of nematodes in wild rodents has been shown to increase coccidian microparasite infection, possibly through competitive release [8,9]. These studies show that ignoring the broader parasite community may crucially underestimate the occurrence and importance of within-host interactions. Mechanistic insights from systems where experimental approaches are possible will be key for the understanding of the role of co-infection in natural populations [15,16]

Methods

Results

Conclusion