An extensive body of theory has developed to model the interplay between pathogens and populations of their host organisms. However, the internal dynamics of pathogens within individual hosts are still much less well understood. We do not yet know the degree to which host nutrition or resource state may drive within-host pathogen dynamics, or may determine the outcome of infection (either host death [the pathogen wins]; persistent or chronic infection [stable host-pathogen coexistence]; or host exclusion of the invading pathogen [the host wins]). In addition, resource availability may affect the internal dynamics of pathogen populations within hosts in ways that have direct implications for infectious disease dynamics at the host population level, where what matters are transmission rates between infected and susceptible hosts, recovery rates, and birth and death rates.
Results/Conclusions
Examples from viral, protozoan, and bacterial pathogens will be used to demonstrate strong effects of host nutrition on within-host pathogen dynamics and host disease states. Moreover, if it is assumed that the internal resource states of hosts can equilibrate quickly to changes in resource supply rates (as do pathogen loads and impacts), then under some circumstances, one can express the rate 'parameters' of Susceptible-Infected-Recovered (SIR) models as functions of resource supply levels. We use this approach to illustrate several interesting dynamical patterns that emerge theoretically from the resource dependencies of internal pathogen dynamics within individual hosts.
