title: Analysis of a summary network of co-infection in humans reveals that parasites interact most via shared resources.
abstract: Simultaneous infection by multiple parasite species (viruses, bacteria, helminths, protozoa or fungi) is commonplace. Most reports show co-infected humans to have worse health than those with single infections. However, we have little understanding of how co-infecting parasites interact within human hosts. We used data from over 300 published studies to construct a network that offers the first broad indications of how groups of co-infecting parasites tend to interact. The network had three levels comprising parasites, the resources they consume and the immune responses they elicit, connected by potential, observed and experimentally proved links. Pairs of parasite species had most potential to interact indirectly through shared resources, rather than through immune responses or other parasites. In addition, the network comprised 10 tightly knit groups, eight of which were associated with particular body parts, and seven of which were dominated by parasite-resource links. Reported co-infection in humans is therefore structured by physical location within the body, with bottom-up, resource-mediated processes most often influencing how, where and which co-infecting parasites interact. The many indirect interactions show how treating an infection could affect other infections in co-infected patients, but the compartmentalized structure of the network will limit how far these indirect effects are likely to spread.
authors.affiliation: Department of Entomology, North Carolina State University, , Raleigh, NC 27695-7613, USA, Department of Animal and Plant Sciences, University of Sheffield, , Alfred Denny Building, Western Bank, Sheffield S10 2TN, UK, Centre for Immunology, Infection and Evolution, Institute of Evolutionary Biology, School of Biological Sciences, Ashworth Labs, University of Edinburgh, , Kings Buildings, West Mains Road, Edinburgh EH9 3JT, UK, Institute of Integrative Biology, University of Liverpool, , Liverpool L69 7ZB, UK, Institute of Evolutionary Biology and Environmental Studies, University of Zürich, , Winterthurerstrasse 190, Zürich 8057, Switzerland.
authors.forename: Emily C
authors.initials: EC
authors.lastname: Griffiths
authors.forename: Amy B
authors.initials: AB
authors.lastname: Pedersen
authors.forename: Andy
authors.initials: A
authors.lastname: Fenton
authors.forename: Owen L
authors.initials: OL
authors.lastname: Petchey
mesh_terms: D000818:Animals; D001424:Bacterial Infections / Q000150:complications / Q000276:immunology* / Q000469:parasitology*; D060085:Coinfection; D006790:Host-Parasite Interactions; D006801:Humans; D008954:Models, Biological; D009181:Mycoses / Q000150:complications / Q000276:immunology* / Q000469:parasitology*; D010271:Parasites / Q000502:physiology; D010272:Parasitic Diseases / Q000150:complications / Q000276:immunology* / Q000469:parasitology*; D014777:Virus Diseases / Q000150:complications / Q000276:immunology* / Q000469:parasitology*
keywords: degree distribution; ecological network; indirect interactions; modularity; parasite ecology; polymicrobial infection