# Severe population collapses and species extinctions in multi-host epidemic dynamics

## TL;DR

This study models multi-host epidemics using a two-species SIR framework, revealing that a single epidemic can cause extinction in vulnerable species co-infected with abundant hosts, highlighting risks beyond endemic disease states.

## Contribution

It introduces a novel multi-host epidemic model to analyze population collapses and extinction risks, extending beyond traditional single-host disease modeling.

## Key findings

- Epidemics can cause extinction of vulnerable species co-infected with abundant hosts.
- Population collapses depend on initial sizes, infectious periods, and infection rate matrices.
- Extinction risks are different from those predicted by endemic steady state models.

## Abstract

Most infectious diseases including more than half of known human pathogens are not restricted to just one host, yet much of the mathematical modeling of infections has been limited to a single species. We investigate consequences of a single epidemic propagating in multiple species and compare and contrast it with the endemic steady state of the disease. We use the two-species Susceptible-Infected-Recovered (SIR) model to calculate the severity of post-epidemic collapses in populations of two host species as a function of their initial population sizes, the times individuals remain infectious, and the matrix of infection rates. We derive the criteria for a very large, extinction-level, population collapse in one or both of the species. The main conclusion of our study is that a single epidemic could drive a species with high mortality rate to local or even global extinction provided that it is co-infected with an abundant species. Such collapse-driven extinctions depend on factors different than those in the endemic steady state of the disease.