Dynamics of host populations affected by the emerging fungal pathogen Batrachochytrium salamandrivorans.

Benedikt R Schmidt,Claudio Bozzuto,Stefan Lötters,Sebastian Steinfartz

doi:10.1098/rsos.160801

Abstract

Emerging infectious diseases cause extirpation of wildlife populations. We use an epidemiological model to explore the effects of a recently emerged disease caused by the salamander-killing chytrid fungus Batrachochytrium salamandrivorans (Bsal) on host populations, and to evaluate which mitigation measures are most likely to succeed. As individuals do not recover from Bsal, we used a model with the states susceptible, latent and infectious, and parametrized the model using data on host and pathogen taken from the literature and expert opinion. The model suggested that disease outbreaks can occur at very low host densities (one female per hectare). This density is far lower than host densities in the wild. Therefore, all naturally occurring populations are at risk. Bsal can lead to the local extirpation of the host population within a few months. Disease outbreaks are likely to fade out quickly. A spatial variant of the model showed that the pathogen could potentially spread rapidly. As disease mitigation during outbreaks is unlikely to be successful, control efforts should focus on preventing disease emergence and transmission between populations. Thus, this emerging wildlife disease is best controlled through prevention rather than subsequent actions.

Highlights

Emerging infectious diseases threaten wildlife populations because they can cause mass mortality, which may lead to local and global extinction of hosts
We use an epidemiological model to investigate the dynamics of a fungal disease in salamanders, caused by Batrachochytrium salamandrivorans (‘the devourer of salamanders’, hereafter Bsal), that recently emerged in Europe [11,12,13,14], with the goal of informing mitigation strategies
Because uncertainties hinder the effective deployment of interventions in areas where Bsal has emerged [18], we modelled the temporal and spatial dynamics of the Bsal–salamander system, with the ultimate goal of informing mitigation strategies

Summary

Introduction

Emerging infectious diseases threaten wildlife populations because they can cause mass mortality, which may lead to local and global extinction of hosts. Such extinctions may cause the loss of evolutionary diversity and can lead to changes in ecosystem function [1,2,3,4]. Bsal emerged in The Netherlands in wild salamander populations, where it caused mass mortality and drove salamander populations to the edge of extirpation [11,12,13] This novel pathogen is of global conservation concern because it could have devastating effects on salamander biodiversity worldwide, as well as knock-on consequences for ecosystem function [17,18]. Since the spread of Bsal is important in our analysis, we considered model formulations reflecting both temporal and spatio-temporal changes

Basic model: temporal formulation

Spatio-temporal formulation

Parameter values

Results

Discussion