title: Interactions among bacterial strains and fluke genotypes shape virulence of co-infection.
abstract: Most studies of virulence of infection focus on pairwise host-parasite interactions. However, hosts are almost universally co-infected by several parasite strains and/or genotypes of the same or different species. While theory predicts that co-infection favours more virulent parasite genotypes through intensified competition for host resources, knowledge of the effects of genotype by genotype (G × G) interactions between unrelated parasite species on virulence of co-infection is limited. Here, we tested such a relationship by challenging rainbow trout with replicated bacterial strains and fluke genotypes both singly and in all possible pairwise combinations. We found that virulence (host mortality) was higher in co-infections compared with single infections. Importantly, we also found that the overall virulence was dependent on the genetic identity of the co-infecting partners so that the outcome of co-infection could not be predicted from the respective virulence of single infections. Our results imply that G × G interactions among co-infecting parasites may significantly affect host health, add to variance in parasite fitness and thus influence evolutionary dynamics and ecology of disease in unexpected ways.
authors.affiliation: Department of Biological and Environmental Science, University of Jyväskylä, PO Box 35, 40014, Jyväskylä, Finland.
authors.forename: Katja-Riikka
authors.initials: KR
authors.lastname: Louhi
authors.affiliation: Department of Biological and Environmental Science, University of Jyväskylä, PO Box 35, 40014, Jyväskylä, Finland Centre of Excellence in Biological Interactions, University of Jyväskylä, PO Box 35, 40014, Jyväskylä, Finland.
authors.forename: Lotta-Riina
authors.initials: LR
authors.lastname: Sundberg
authors.affiliation: Eawag, Swiss Federal Institute of Aquatic Science and Technology, 8600 Dübendorf, Switzerland ETH Zürich, Institute of Integrative Biology, 8092 Zürich, Switzerland.
authors.forename: Jukka
authors.initials: J
authors.lastname: Jokela
authors.affiliation: Department of Biological and Environmental Science, University of Jyväskylä, PO Box 35, 40014, Jyväskylä, Finland anssi.t.karvonen@jyu.fi.
authors.forename: Anssi
authors.initials: A
authors.lastname: Karvonen
mesh_terms: D000818:Animals; D005393:Fish Diseases / Q000382:microbiology* / Q000469:parasitology*; D045826:Flavobacteriaceae Infections / Q000382:microbiology / Q000662:veterinary*; D005417:Flavobacterium / Q000235:genetics*; D005838:Genotype; D054884:Host-Pathogen Interactions; D017686:Oncorhynchus mykiss / Q000382:microbiology* / Q000469:parasitology*; D014200:Trematoda / Q000235:genetics*; D014201:Trematode Infections / Q000469:parasitology / Q000662:veterinary*; D014774:Virulence / Q000235:genetics
keywords: Diplostomum pseudospathaceum; Flavobacterium columnare; concomitant infection; epidemiology; facilitation; multiple infection