title: Outside-host growth of pathogens attenuates epidemiological outbreaks.
abstract: Opportunist saprotrophic pathogens differ from obligatory pathogens due to their capability in host-independent growth in environmental reservoirs. Thus, the outside-host environment potentially influences host-pathogen dynamics. Despite the socio-economical importance of these pathogens, theory on their dynamics is practically missing. We analyzed a novel epidemiological model that couples outside-host density-dependent growth to host-pathogen dynamics. Parameterization was based on columnaris disease, a major hazard in fresh water fish farms caused by saprotrophic Flavobacterium columnare. Stability analysis and numerical simulations revealed that the outside-host growth maintains high proportion of infected individuals, and under some conditions can drive host extinct. The model can show stable or cyclic dynamics, and the outside-host growth regulates the frequency and intensity of outbreaks. This result emerges because the density-dependence stabilizes dynamics. Our analysis demonstrates that coupling of outside-host growth and traditional host-pathogen dynamics has profound influence on disease prevalence and dynamics. This also has implications on the control of these diseases.
authors.affiliation: Department of Biosciences, University of Helsinki, Helsinki, Finland. ilona.merikanto@helsinki.fi
authors.forename: Ilona
authors.initials: I
authors.lastname: Merikanto
authors.forename: Jouni
authors.initials: J
authors.lastname: Laakso
authors.forename: Veijo
authors.initials: V
authors.lastname: Kaitala
mesh_terms: D000818:Animals; D003198:Computer Simulation; D004196:Disease Outbreaks / Q000517:prevention & control*; D004197:Disease Reservoirs / Q000382:microbiology*; D005393:Fish Diseases / Q000453:epidemiology* / Q000382:microbiology; D005398:Fisheries; D005399:Fishes / Q000382:microbiology*; D045826:Flavobacteriaceae Infections / Q000453:epidemiology* / Q000382:microbiology / Q000662:veterinary*; D005417:Flavobacterium / Q000254:growth & development*; D005618:Fresh Water / Q000382:microbiology*; D054884:Host-Pathogen Interactions; D008954:Models, Biological