On the space‐time evolution of a cholera epidemic

Abstract

[1] We study how river networks, acting as environmental corridors for pathogens, affect the spreading of cholera epidemics. Specifically, we compare epidemiological data from the real world with the space-time evolution of infected individuals predicted by a theoretical scheme based on reactive transport of infective agents through a biased network portraying actual river pathways. The data pertain to a cholera outbreak in South Africa which started in 2000 and affected in particular the KwaZulu-Natal province. The epidemic lasted for 2 years and involved about 140,000 confirmed cholera cases. Hydrological and demographic data have also been carefully considered. The theoretical tools relate to recent advances in hydrochory, migration fronts, and infection spreading and are novel in that nodal reactions describe the dynamics of cholera. Transport through network links provides the coupling of the nodal dynamics of infected people, who are assumed to reside at the nodes. This proves a realistic scheme. We argue that the theoretical scheme is remarkably capable of predicting actual outbreaks and, indeed, that network structures play a controlling role in the actual, rather anisotropic propagation of infections, in analogy to spreading of species or to migration processes that also use rivers as ecological corridors.

On spatially explicit models of cholera epidemics

“…To this aim, we have generalized a spatially explicit model of cholera first proposed by Bertuzzo et al (2008) for discussing the outbreaks that occurred in the KwaZuluNatal province, South Africa, from 2000 to 2002. To keep our analysis as general as possible and to provide a theoretical understanding of the reaction-advection-diffusion process, we have used here four different topologies, namely, one-and two-dimensional regular lattices, Peano networks and OCNs.…”

“…Recalling that in a diffusion process the average distance travelled by a particle at time t scales as p Dt, we can state that, in order to have cholera-spreading inland, vibrios should be transported at approximately 0.74 km in 1 day. With the stronger drift of 3 km d 21 (as in Bertuzzo et al 2008), this distance is 2.2 km d 21 . These are plausible values given the transport processes involved.…”

“…The network acts as a matrix through which different sets of water supplies of different communities can be connected and contaminated. In the following, the epidemiological and demographic parameter values employed are those that best fit the real epidemics analysed in Bertuzzo et al (2008)…”

“…The analysis proposed in this paper is instead based on spatially explicit models that explicitly account for the environmental matrix along which the disease can spread. These models were used in Bertuzzo et al (2008) to simulate the specific case of the KwaZulu-Natal 2001-2002 epidemic via a suitable tuning of their parameters. They are now considered in greater generality to analyse the effects of different hydrological networks and disease dynamics on the epidemic evolution.…”

Spatially Explicit Conditions for Waterborne Pathogen Invasion

“…While some diarrheal infections are basically linked to fecal-oral direct transmission (e.g., rotavirus) and their dynamics can thus be modeled as SIR (susceptibleinfected-recovered) systems (Pitzer et al 2009), the spatial spread of waterborne diseases is mediated primarily by the hydrological network (Bertuzzo et al 2008(Bertuzzo et al , 2010Akanda et al 2009). However, in many cases, human mo-bility plays an additional important role.…”