Cascading effects of predator activity on tick-borne disease risk.

Tim R Hofmeester,Patrick A Jansen,Hein Sprong,Hendrikus J Wijnen,Herbert H T Prins,Manoj Fonville,Sipke E Van Wieren,Elena C Coipan

doi:10.1098/rspb.2017.0453

Abstract

Predators and competitors of vertebrates can in theory reduce the density of infected nymphs (DIN)—an often-used measure of tick-borne disease risk—by lowering the density of reservoir-competent hosts and/or the tick burden on reservoir-competent hosts. We investigated this possible indirect effect of predators by comparing data from 20 forest plots across the Netherlands that varied in predator abundance. In each plot, we measured the density of questing Ixodes ricinus nymphs (DON), DIN for three pathogens, rodent density, the tick burden on rodents and the activity of mammalian predators. We analysed whether rodent density and tick burden on rodents were correlated with predator activity, and how rodent density and tick burden predicted DON and DIN for the three pathogens. We found that larval burden on two rodent species decreased with activity of two predator species, while DON and DIN for all three pathogens increased with larval burden on rodents, as predicted. Path analyses supported an indirect negative correlation of activity of both predator species with DON and DIN. Our results suggest that predators can indeed lower the number of ticks feeding on reservoir-competent hosts, which implies that changes in predator abundance may have cascading effects on tick-borne disease risk.

Highlights

The incidence of zoonotic vector-borne diseases has increased in recent decades [1]
We first explored the data by testing for correlations between: (i) bank vole or wood mouse density, (ii) larval burden on bank voles or wood mice, or (iii) nymphal burden on bank voles or wood mice (GLMMs with negative binomial distribution and log link) and the activity of the different predator species that we detected in our plots using the dredge function in the MuMIn package [37]
We found large variation between plots in the density of infected nymphs (DIN) for B. afzelii, B. miyamotoi and Ca

Summary

Introduction

The incidence of zoonotic vector-borne diseases has increased in recent decades [1]. In northwestern Europe and northeastern North America, many of these are caused by pathogens that are transmitted by ticks from the Ixodes ricinus complex: I. ricinus in Europe and Ixodes scapularis in North America [1,2]. We first explored the data by testing for correlations between: (i) bank vole or wood mouse density, (ii) larval burden on bank voles or wood mice, or (iii) nymphal burden on bank voles or wood mice (GLMMs with negative binomial distribution and log link) and the activity of the different predator species that we detected in our plots using the dredge function in the MuMIn package [37]. We explored correlations between rodent density, larval burden and nymphal burden (per species) with the density of questing nymphs (DON) and the DIN for all three pathogens using GLMMs with a negative binomial distribution and log link. We determined and tested the independence claims for the causal models (electronic supplementary material, S3) and calculated C values as described by Shipley [39] for each of the combinations of DON and DIN for the different pathogens per rodent species. We used a x2-test to test for differences in observed prevalence of co-infections with the different pathogens in all questing nymphs, and expected prevalence of co-infections based on the infection prevalence of the separate pathogens, to test for associations between the pathogens

Results

Discussion

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