Within-host dynamics of multi-species infections: facilitation, competition and virulence.
Host individuals are often infected with more than one parasite species (parasites defined broadly, to include viruses and bacteria). Yet, research in infection biology is dominated by studies on single-parasite infections. A focus on single-parasite infections is justified if the interactions among parasites are additive, however increasing evidence points to non-additive interactions being the norm. Here we review this evidence and theoretically explore the implications of non-additive interactions between co-infecting parasites. We use classic Lotka-Volterra two-species competition equations to investigate the within-host dynamical consequences of various mixes of competition and facilitation between a pair of co-infecting species. We then consider the implications of these dynamics for the virulence (damage to host) of co-infections and consequent evolution of parasite strategies of exploitation. We find that whereas one-way facilitation poses some increased virulence risk, reciprocal facilitation presents a qualitatively distinct destabilization of within-host dynamics and the greatest risk of severe disease.
Department of Cell Biology, Lerner Research Institute, Cleveland Clinic, Cleveland, Ohio, United States of America. eswaras@ccf.org
Sandeepa M
SM
Eswarappa
Sylvie
S
Estrela
Sam P
SP
Brown
D000818:Animals; D005075:Biological Evolution; D060085:Coinfection; D006790:Host-Parasite Interactions; D006801:Humans; D008954:Models, Biological; D015233:Models, Statistical; D010272:Parasitic Diseases / Q000469:parasitology* / Q000503:physiopathology*; D012306:Risk; D013045:Species Specificity; D013997:Time Factors; D014774:Virulence