Spreading of Persistent Infections in Heterogeneous Populations

TL;DR

This paper investigates how persistent infections like tuberculosis spread in heterogeneous populations, revealing that epidemic thresholds depend on network degree distribution and tend to vanish in scale-free networks as population size grows.

Contribution

It introduces a novel epidemiological model for persistent diseases considering population heterogeneity and analyzes the epidemic threshold behavior in complex networks.

Findings

Epidemic threshold depends on the ratio of the first two moments of degree distribution.

Threshold approaches zero in scale-free networks as system size increases.

Persistent diseases can spread extensively in heterogeneous populations.

Abstract

Up to now, the effects of having heterogeneous networks of contacts have been studied mostly for diseases which are not persistent in time, i.e., for diseases where the infectious period can be considered very small compared to the lifetime of an individual. Moreover, all these previous results have been obtained for closed populations, where the number of individuals does not change during the whole duration of the epidemics. Here, we go one step further and analyze, both analytically and numerically, a radically different kind of diseases: those that are persistent and can last for an individual's lifetime. To be more specific, we particularize to the case of Tuberculosis' (TB) infection dynamics, where the infection remains latent for a period of time before showing up and spreading to other individuals. We introduce an epidemiological model for TB-like persistent infections taking into account the heterogeneity inherent to the population structure. This sort of dynamics introduces new analytical and numerical challenges that we are able to sort out. Our results show that also for persistent diseases the epidemic threshold depends on the ratio of the first two moments of the degree distribution so that it goes to zero in a class of scale-free networks when the system approaches the thermodynamic limit.