The impact of multiple infections on wild animal hosts: a review

Bordes, Frédéric; Morand, Serge

In natural conditions, hosts are infected by multiple parasite species or by multiple genotypes of the same parasite species. Multiple infections have often been investigated through the analyses of the outcomes of competition among parasites. Competition during multiple infections includes both interspecific competition (e.g. mixed species helminth infection) and/or intraspecific competition (e.g. genetically diverse strains of microparasites). Fundamentally, competition between parasites may be direct or indirect, through competition for resources (e.g. blood) or immune system (i.e. immunesuppression or cross-immunity) (16, 17) . The relative importance of the forces that determine the structure of parasite communities, resources or immunity, may then provide some consequences of multiple infections. During multiple infections with two or more parasite species, the burden of one (or more) parasite(s) might be enhanced by the other parasite(s) (synergic interactions) or, on the contrary, be suppressed (antagonist interactions) (18, 19) . The recent study of Telfer and colleagues (20) has highlighted that parasitic interactions can explain more variation in infection risks than factors related to parasite exposure, host age and/or seasonality.