Front propagation in hybrid reaction-diffusion epidemic models with spatial heterogeneity. Part I: Spreading speed and asymptotic behavior

TL;DR

This paper analyzes a complex reaction-diffusion epidemic model with two pathogens in a heterogeneous environment, establishing spreading speeds, convergence to stationary solutions, and effects of spatial heterogeneity and homogenization.

Contribution

It introduces a hybrid two-species reaction-diffusion model with spatial heterogeneity, studying spreading speeds, stationary solutions, and homogenization effects, which are novel in this context.

Findings

Existence of well-defined spreading speeds in both directions.

Solutions converge to a unique positive stationary solution over time.

Homogenization limit as spatial heterogeneity becomes rapid.

Abstract

We consider a two-species reaction-diffusion system in one space dimension that is derived from an epidemiological model in a spatially periodic environment with two types of pathogens: the wild type and the mutant. The system is of a hybrid nature, partly cooperative and partly competitive, but neither of these entirely. As a result, the comparison principle does not hold for the whole system. We study spreading properties of solution fronts when the infection is localized initially. We show that there is a well-defined spreading speed both in the right and left directions and that it can be computed from the linearized equation at the leading edge of the propagation front. Next we study the case where the coefficients are spatially homogeneous and show that, when spreading occurs, every solution to the Cauchy problem converges to the unique positive stationary solution as $t\to\infty$. Finally we consider the case of rapidly oscillating coefficients, that is, when the spatial period of the coefficients, denoted by $\varepsilon$, is very small. We show that there exists a unique positive stationary solution, and that every positive solution to the Cauchy problem converges to this stationary solution as $t\to\infty$. We then discuss the homogenization limit as $\varepsilon\to 0$.