Indirect transmission and the effect of seasonal pathogen inactivation on infectious disease periodicity

TL;DR

This paper presents a model explaining how seasonal environmental inactivation of pathogens influences the periodicity of infectious diseases, highlighting the role of pathogen lifespan and environmental factors in disease dynamics.

Contribution

It introduces a mathematical model incorporating seasonal pathogen inactivation, revealing its impact on disease oscillations and the timing of peak incidences.

Findings

Seasonal pathogen inactivation causes disease incidence oscillations.

The delay between pathogen survival peak and disease peak depends on disease parameters.

Oscillation period matches seasonal inactivation cycle, independent of immunity duration.

Abstract

The annual occurrence of many infectious diseases remains a constant burden to public health systems. The seasonal patterns in respiratory disease incidence observed in temperate regions have been attributed to the impact of environmental conditions on pathogen survival. A model describing the transmission of an infectious disease by means of a pathogenic state capable of surviving in an environmental reservoir outside of its host organism is presented in this paper. The ratio of pathogen lifespan to the duration of the infectious disease state is found to be a critical parameter in determining disease dynamics. The introduction of a seasonally forced pathogen inactivation rate identifies a time delay between peak pathogen survival and peak disease incidence. The delay is dependent on specific disease parameters and, for influenza, decreases with increasing reproduction number. The observed seasonal oscillations are found to have a period identical to that of the seasonally forced inactivation rate and which is independent of the duration of infection acquired immunity