Lethal exposure: An integrated approach to pathogen transmission via environmental reservoirs.

Wendy C Turner,Zoë R Barandongo,Wolfgang Beyer,Matthew N Van Ert,Peter C B Turnbull,Nils Chr Stenseth,Elisabeth Blaschke,Claudine C Cloete,Holly H Ganz,Kyrre L Kausrud,Judith Lazak,Wayne M Getz,W Ryan Easterday

doi:10.1038/srep27311

Abstract

To mitigate the effects of zoonotic diseases on human and animal populations, it is critical to understand what factors alter transmission dynamics. Here we assess the risk of exposure to lethal concentrations of the anthrax bacterium, Bacillus anthracis, for grazing animals in a natural system over time through different transmission mechanisms. We follow pathogen concentrations at anthrax carcass sites and waterholes for five years and estimate infection risk as a function of grass, soil or water intake, age of carcass sites, and the exposure required for a lethal infection. Grazing, not drinking, seems the dominant transmission route, and transmission is more probable from grazing at carcass sites 1–2 years of age. Unlike most studies of virulent pathogens that are conducted under controlled conditions for extrapolation to real situations, we evaluate exposure risk under field conditions to estimate the probability of a lethal dose, showing that not all reservoirs with detectable pathogens are significant transmission pathways.

Highlights

To mitigate the effects of zoonotic diseases on human and animal populations, it is critical to understand what factors alter transmission dynamics
Though progress is being made in risk assessment studies, more data are needed on diseases currently posing threats to public health, livestock health, and wildlife health
We found a strong positive relationship between the estimates of Bacillus anthracis (BA) concentrations in soils from culture and qPCR (t = 7.81, p < 0.0001, R2 = 0.504, N = 62 sites), the estimates diverged from a 1:1 line as concentrations increased beyond approximately 104 colony forming units (CFU)/g (Fig. 3) and our DNA extraction efficiency from spores was low at 7.8 ± 5.7%

Summary

Introduction

To mitigate the effects of zoonotic diseases on human and animal populations, it is critical to understand what factors alter transmission dynamics. We assess the risk of exposure to lethal concentrations of the anthrax bacterium, Bacillus anthracis, for grazing animals in a natural system over time through different transmission mechanisms. The distribution of infectious agents in the environment is typically aggregated due to pulsed releases from infected hosts, creating heterogeneity in the risk of exposure for future hosts. The challenge for risk assessment in wildlife disease systems is a lack of data on natural exposure levels and dose-response relationships that link exposure to host response (i.e. infection, resistance, tolerance[9]). An effective contact is equal to a lethal contact, making this an ideal study system for exploring exposure levels through different pathogen sources and transmission pathways

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