Browsing by Subject "opportunistinen taudinaiheuttaja"

Many pathogens are able to survive and reproduce in the environment outside of host for instance by saprotrophic lifestyle. These kinds of pathogens are called opportunistic as compared to obligatory pathogens that cannot interact or reproduce in the environment outside of host. Opportunistic pathogens are subject to strong selection forces in the environment outside of host for instance while they compete for resources they share with other microbes. Ecological interactions in the environment outside of host can therefore influence on the disease dynamics and evolution of virulence of an opportunistic pathogen. No proper theoretical model that would acknowledge opportunistic reproduction and ecological interactions in the environment out side of host has been developed before. Yet it is essential to develop this kind of theoretical model so that the development and dynamics of opportunistic diseases could be predicted and prevented. In this work, an opportunistic disease model was developed that considers both the opportunistic reproduction and the influence of a superior competitor as compared to pathogenic strain on pathogen growth in the environment outside of host. Differential equations in the model represent the density changes in time in the populations of susceptible and infected host, pathogen and rival strain outside host that is not pathogenic. Evolution of virulence of the new opportunistic pathogen meaning the ability to grow from low density in presence of superior competing strain was modeled in differing circumstances. Opportunistic disease dynamics was modeled in differing circumstances, when non-pathogenic competing strain was either present or absent. Equilibrium equations were solvable to a system, where non-pathogenic competing strain was absent, but to a system where non-pathogenic competing strain was present. Analyses of the model were performed with Math Works MATLAB – program. Reproducing inside host gives an opportunity for new opportunistic pathogen to increase in density under circumstances where competition is moderate enough so that the reproduction in the environment outside host may compensate opportunistic pathogen's weaker ability to compete. Reproduction and competition in the environment outside host produce disease dynamics that differ from more traditional SI-models. Density dependence of the reproduction in the environment outside host stabilizes host-parasite system in the absence of competition in the environment outside host. Instead, in the presence of competition the competitive advantage of the non-pathogen strain destabilizes disease dynamics and prevents extinction of the susceptible host. Reproduction in the environment outside host also enables opportunistic pathogen to remain in the environment in the absence of susceptible hosts and functions thus as a potential mechanism for disease out breaks when circumstances change. However, increasing competition in the environment outside host at the expense of opportunistic pathogen may potentially prevent epidemics. Among other things, the model could be applied to biological control with the intension of removing an opportunistic pathogen naturally by weakening its survival in the environment out side of host in a competiotion situation. This kind of biological control could for example be possible in the case of saprotrophic Flavobacterium columnare –fish pathogen that is found in fish farms.