Models with environmental drivers offer a plausible mechanism for the rapid spread of infectious disease outbreaks in marine organisms

E A Aalto,G A De Leo,C A Boch,E L Hazen,S J Bograd,P T Raimondi,M G Jacox,F Micheli,R E Grewelle,S H Sokolow,T Ben-Horin,K D Lafferty

doi:10.1038/s41598-020-62118-4

E A Aalto, G A De Leo + Show 10 more

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https://doi.org/10.1038/s41598-020-62118-4

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Abstract

The first signs of sea star wasting disease (SSWD) epidemic occurred in just few months in 2013 along the entire North American Pacific coast. Disease dynamics did not manifest as the typical travelling wave of reaction-diffusion epidemiological model, suggesting that other environmental factors might have played some role. To help explore how external factors might trigger disease, we built a coupled oceanographic-epidemiological model and contrasted three hypotheses on the influence of temperature on disease transmission and pathogenicity. Models that linked mortality to sea surface temperature gave patterns more consistent with observed data on sea star wasting disease, which suggests that environmental stress could explain why some marine diseases seem to spread so fast and have region-wide impacts on host populations.

Highlights

The first signs of sea star wasting disease (SSWD) epidemic occurred in just few months in 2013 along the entire North American Pacific coast
The effects of climate on disease transmission cannot be isolated through statistical analysis, because the size of disease outbreaks may depend on both climate influences and the abundance of susceptible and infectious individuals in the host population, which interact in a non-linear fashion to produce the observed disease dynamics[26]
The model simulates disease dynamics on a linearized Pacific coastline divided into 500 5-km cells, each representing a local sea star population subject to infective propagules that disperse, through diffusion/advection, between neighboring cells according to local ocean currents (Fig. 1c; linearization described in Appendix A)

Summary

Introduction

The first signs of sea star wasting disease (SSWD) epidemic occurred in just few months in 2013 along the entire North American Pacific coast. Models that linked mortality to sea surface temperature gave patterns more consistent with observed data on sea star wasting disease, which suggests that environmental stress could explain why some marine diseases seem to spread so fast and have region-wide impacts on host populations. With a few notable exceptions[27,36], the majority of studies of human infectious disease have either spatially aggregated data when analyzing variance of incidence over time[25,26] or analyzed regional-scale variations in prevalence purely as a function of climate drivers without accounting for temporal dynamics in the abundance of susceptible and infected populations. No clear environmental trigger has been identified, temperature correlates with infected mortality rates in adult sea stars[37,38], and some die-offs occurred during when it was warmer than usual (e.g., in the Channel Islands[39] and Washington[40] though not Oregon[41]). As a complement to these studies, we contrasted possible mechanistic models for widespread marine epidemics like SSWD with different degrees of temperature-dependence

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