Pathogen spillover in a seasonal cholera model.

The risk of pathogen spillover from a natural reservoir to a host population, or from an infectious host population to an environmental reservoir is a major concern in the emergence and re-emergence of infectious diseases. Understanding the source of the pathogen and the environmental conditions driving the emergence or re-emergence are vital to prevention and control. We investigate pathogen spillover in a well-known infectious disease, cholera, where the environment harboring the bacterial pathogen is the natural reservoir. Applying a stochastic seasonal cholera model and methods from continuous-time Markov chains and branching process approximations, the probabilities of spillover and disease emergence are computed. In addition, we propose a new estimate for the risk of disease emergence given there is a spillover. Branching process methods provide new insights about seasonal spillover and disease emergence during the early stages of infection.