The roles of direct and environmental transmission in stochastic avian flu epidemic recurrence

TL;DR

This paper analyzes how direct and environmental transmission routes influence the recurrence and intensity of avian flu outbreaks, highlighting their combined effects on epidemic periodicity and amplitude.

Contribution

It introduces an approximation method to simulate noise-driven oscillations in a stochastic avian flu model considering both transmission routes, providing new insights into outbreak dynamics.

Findings

Environmental transmission significantly affects outbreak periodicity.

Both transmission routes contribute to higher outbreak amplitudes.

Intrinsic frequency predicts the dominant outbreak period.

Abstract

We present an analysis of an avian flu model that yields insight into the role of different transmission routes in the recurrence of avian influenza epidemics. Recent modelling work on avian influenza in wild bird populations takes into account demographic stochasticity and highlights the importance of environmental transmission in determining the outbreak periodicity, but only for a weak between-host transmission rate. We determine the relative contribution of environmental and direct transmission routes to the intensity of outbreaks. We use an approximation method to simulate noise sustained oscillations in a stochastic avian flu model with environmental and direct transmission routes. We see that the oscillations are governed by the product of a rotation and a slowly varying standard Ornstein-Uhlenbeck process (i.e., mean-reverting process). The intrinsic frequency of the damped deterministic version of the system predicts the dominant period of outbreaks. We show, using analytic computation of the intrinsic frequency and theoretical power spectral density, that the outbreak periodicity can be explained in terms of either or both types of transmission.The amplitude of outbreaks tends to be high when both types of transmission are strong.