Species Interactions in a Parasite Community Drive Infection Risk in a Wildlife Population

Abstract

Most hosts, including humans, are simultaneously or sequentially infected with several parasites. A key question is whether patterns of coinfection arise because infection by one parasite species affects susceptibility to others or because of inherent differences between hosts. We used timeseries data from individual hosts in natural populations to analyze patterns of infection risk for a microparasite community, detecting large positive and negative effects of other infections. Patterns remain once variations in host susceptibility and exposure are accounted for. Indeed, effects are typically of greater magnitude, and explain more variation in infection risk, than the effects associated with host and environmental factors more commonly considered in disease studies. We highlight the danger of mistaken inference when considering parasite species in isolation rather than parasite communities.Macroparasites (helminths and arthropods) and microparasites (viruses, bacteria, and protozoa) are integral components of the ecological communities that include their hosts (1), and it is likely that most hosts, most of the time, are infected with more than one parasite species (2). Interactions between parasites in natural populations, however, have been studied only rarely. A community ecology perspective is particularly relevant for studies of coinfection, as parasites may interact directly by competing for resources or indirectly via the host immune system (3). Interactions may be antagonistic to at least one of the parasites, either as a result of resource shortage or where there are cross-effective immune responses, or they may be beneficial to one or both parasites, as a result of parasite-induced immunosuppression or down-regulation of all or part of the immune system (1). Table 1 for details of their biology). Infection risk will depend on both the probability of encountering an infectious dose and the probability of infection given exposure (host susceptibility). We aimed to determine whether susceptibility to infection by a microparasite was influenced by other microparasites. Therefore, for each microparasite, we investigated whether the other microparasites influenced the probability that a susceptible animal became infected at a given time point (t 0 ), adding infection status for these other microparasites as explanatory variables to baseline statistical models that accounted for environmental and individual variables (e.g., sex and season) (12) (table S1). Thus, we guard against detecting spurious associations, which, in reality, reflect correlated exposure risk (e.g., a positive association simply because both parasites are most prevalent in late summer). For parasites causing self-limiting infections, infection status at both t 0 and/ or the previous month (t −1 ) were considered as explanatory variables, whereas for B. microti infections, which are chronic, a three-level covariate was used: uninfected, newly infected (infected at t 0 but not before), and chronically infected (first infected prior ...

MHC influences infection with parasites and winter survival in the root vole Microtus oeconomus

“…In voles, the infections are usually subclinical and persistent . The risk of infection depends on coinfection with other parasite species (Telfer et al 2010), however in the current paper, we found no such interactions.…”

“…Significant effects of alleles after controlling for false discovery rate are marked with asterisks. b parameter estimate, df degrees of freedom, v 2 statistics, p probability Evol Ecol (2013) 27:635-653 647 represent the sole explanation for the increased mortality of infected animals (Telfer et al 2010), and their effect on host populations often depends on other factors, such as host sex (Fuller and Blaustein 1996) or food availability (Murray et al 1996). Here, we studied survival over the winter, which is the period when the tight energy budget of animals may make the negative effects of parasite infection particularly pronounced.…”

Longitudinal field study on bovine Babesia spp. and Anaplasma phagocytophilum infections during a grazing season in Belgium

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