Fate and Transport of Zoonotic Bacterial, Viral, and - The Pork Store ...

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Fate and Transport of Zoonotic Bacterial, Viral, and Parasitic Pathogens during Swine Manure Treatment, Storage, and Land Application
studies and other sources of scientific data are
used to estimate microbial distributions in each
compartment and to describe the mathematical
relationships that characterize the fate of microbes
between compartments. Table 5.1 outlines a
risk assessment framework for estimating the
environmental burden of zoonotic pathogens from
swine facilities.
An advantage of stochastic modeling is the
ability to quantitatively assess and analyze the
roles of both data uncertainty and variability on
risk estimates. During the hazard identification
and exposure assessments, gaps in the scientific
database can be identified, and the impact of these
gaps on the estimate of the burden of zoonotic
pathogens in the environment can be evaluated.
The results of a QRA can be used to identify
research needs that will contribute most effectively
to understanding the environmental contamination
risks associated with swine production facilities. As
additional scientific data become available, they can
be incorporated into the model easily.
A disadvantage of the QRA framework is that
it reduces complex ecological systems to a relatively
simple model of microbial fate and the resultant
human exposure. Consequently, risk estimates
may not prove to be robust as the understanding
of microbial ecology and environmental systems
increases. Nonetheless, the QRA can be used to
estimate the environmental burden of zoonotic
pathogens and the attendant risks that are too low
to be measured by field studies and can help to
identify specific research needs.
In spite of a technologically advanced
industry that places emphasis on animal health and
management, zoonotic pathogens are not likely to
disappear from swine manure management systems.
Although bench top and environmental field data
suggest that there may be a biologically significant level
of viable pathogens in the environment that may be
associated with modern swine production, these levels
often are too low to quantify easily. In this setting,
quantitative risk assessment may serve to bridge the gap
between bench top studies and environmental science to
provide an estimate of the risk that is difficult to assess
using traditional field science methods.
Table 5.1 Components of a Quantitative risk Assessment Framework to estimate the human
health risks associated with zoonotic pathogens in the swine production environment
Steps in QRA Conceptual model Variables
Hazard Characterization of zoonotic • Stage of production
identification pathogens in swine manure • Disease status of animals
• Microbe characteristics
Swine waste as a source of
zoonotic pathogens
•
•
•
Stage of production
Prevalence and density of pathogen in untreated wastes
Pathogen reductions achieved by waste storage and
Exposure
assessment
Movement from wasteholding
facilities to
environmental media
•
•
•
•
treatment technology
Storage and treatment methods
Ecologically-significant processes among environmental
microbes and pathogens
Pathogen characteristics
Soil characteristics
• Environmental conditions
Dose-response Biologically-relevant level of • Pathogen characteristics
assessment pathogen in environment • Proximity of vulnerable resources
Risk
characterization
Environmental risk resulting
from swine-manureassociated
contamination
• Frequency and duration of environmental contamination
• Pathogen characteristics