Mathematically Modeling Spillover Dynamics of Emerging Zoonoses with Intermediate Hosts

TL;DR

This paper develops a mathematical model to understand how zoonotic diseases mutate and spread through wild, domestic, and human hosts, providing insights into emergence conditions and stability of disease states.

Contribution

It introduces a comprehensive transmission model across three host species and derives conditions for disease emergence and stability, aiding zoonosis control strategies.

Findings

A zoonotic disease can persist in humans even if it dies out in reservoir and intermediate hosts.

The basic reproductive number is calculated for complex multi-host systems.

Model predictions align with long-term simulations of disease dynamics.

Abstract

The World Health Organization describes zoonotic diseases as a major pandemic threat, and modeling the behavior of such diseases is a key component of their control. Many emerging zoonoses, such as SARS, Nipah, and Hendra, mutated from their wild type while circulating in an intermediate host population, usually a domestic species, to become more transmissible among humans, and moreover, this transmission route will only become more likely as agriculture and trade intensifies around the world. Passage through an intermediate host enables many otherwise rare diseases to become better adapted to humans, and so understanding this process with mathematical epidemiological models is necessary to prevent epidemics of emerging zoonoses, guide policy interventions in public health, and predict the behavior of an epidemic. In this paper, we account for spillovers of a zoonotic disease mutating in an intermediate host by means of modeling transmission dynamics within and between three host species, namely, wild reservoir, intermediate domestic animals, and humans. We calculate the basic reproductive number of the pathogen, present critical conditions for the emergence dynamics of zoonosis, and perform stability analysis of admissible disease equilibria. Our analytical results agree well with long-term simulations of the system. We find that in the presence of biologically realistic interspecies transmission parameters, a zoonotic disease can establish itself in humans even if it fails to persist in its reservoir and intermediate host species. Our model and results can be used to understand the dynamic behavior of any zoonosis with intermediate hosts and assist efforts to protect public health.