The Role Of The Aquatic Reservoir In Long-Term Cholera Dynamics

A novel class of models for Cholera epidemics is described, where the dynamics of the water volume defining the aquatic reservoir of pathogens accessible to a given local community is explicitly considered. In particular, we study how the hydrologic dynamics affects the fluctuations of Vibrio cholerae concentrations in the local reservoir thus driving the evolution of the epidemics at local scales. The novelty of the approach lies in the coupling of an input-output hydrologic dynamics with an epidemiological model which tracks susceptibles, infected and recovered individuals, jointly with bacterial concentrations. Reservoir volumes fluctuating over time indeed control the concentrations of Vibrio cholerae: one of the most common mechanisms of cholera insurgence in endemic regions is, in fact, spring water drought. Here we consider a spatially implicit framework, in order to distinguish the contribution of local dynamics to cholera insurgence at community scales. Our main goal is to investigate the relation between yearly water volume oscillations and long-term trajectories of cholera infection. To this end we take into account a monsoonal fluctuation, with one summer peak in the water input. This simple addition allows us to derive relationships between hydrologic regimes and the epidemiological behavior of the system. Since most of the numerical values of model parameters can be reliably drawn from the literature on the subject, this method allows us to concentrate on significant but still uncertain quantities and associate different ranges of parameter values to different model behaviors which need to be clearly differentiated . Our analysis provides information on the characteristic value of the model parameters for real case studies, comparing simulations and real time series. The model can be very useful in particular for the inference of the intensity of the disease, expressed in terms of the basic reproductive number.