Bistable host-pathogen interaction explains varied infection outcomes

Death or survival are the two outcomes of an infection. The development of an infection depends on multiple interplaying factors, including the temporal dynamic of host nutrition, immune response and pathogen proliferation, but how these factors collectively determine the outcome of an infection is less understood. To understand the underlying principle of infection, here, we took a systems approach by developing a simple mathematical model to understand multi-factored host-pathogen interaction. We find that nonlinear interactions feedback between host and pathogens resulting in two distinct trajectories of disease progression. We show that disease progression, measured by the pathogen load, responds in a bistable manner, by either proliferating or eventually being eliminated. We identified key processes accounting for bistability, including hosts resource assimilation, immune response and intrinsic noise. In addition, resource availability, immunity, and pathogen load at the onset of infection are also critical in determining the bistability. We then highlight, by discussing in the light of previous theoretical and experimental work, how our framework provides testable theories for host-pathogen interaction inside the host.