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
similar resistance to extreme pHs and may be a better
surrogate for the HuNoVs than the frequently used
FeCV (Cannon et al. 2006). Organic acids are unlikely
to have any effect on the viability of these viruses during
short contact times (Seymour and Appleton 2001).
Presence and Fate
Limited data are available on the behavior of viruses
or their possible surrogates in manure and soil. In the
particular case of animal enteric caliciviruses (NoVs
and SaVs), at least two factors should be highlighted.
First, these viruses and their presence and prevalence
only recently have been reported; and second, and
perhaps more importantly, there is a lack of cell culture
for assessment of virus infectivity for human NoVs and
SaVs. The latter deficiency necessitates assessment of
the environmental survival of these viruses through
a surrogate virus such as FeCV using lab-scale assays.
There are two difficulties with this approach: the first
is to understand whether a nonenteric virus—such as
FeCV—adequately reflects the stability of the surrogate
enteric virus. A good correlation was observed when
FeCV and HuNoVs were inactivated by heat, UV, or free
chlorine, but only HuNoVs remained infectious when
the pH was lower than 3 (Dolin et al. 1972; Duizer et al.
2004). The second difficulty results from the fact that the
true environmental scenario cannot be replicated fully in
a laboratory, because multiple and simultaneous factors
affect virus survival in the field.
Land application of agricultural manure occurs
worldwide, and pathogens present in manure can affect
soil and water integrity. Different environmental factors
affect the fate and transport of pathogens from manure
into soil and water. In lab-scale experiments, microbial
concentrations initially decline with time when added
to a solution, but thereafter remain basically constant
as indicated by studies of Slomka and Appleton (1998)
using seawater. This study showed that a 20-fold decrease
in FeCV infectivity occurs on addition to seawater, but
no significant decrease occurs in the next 24 hr. But
in the field this also depends on the equilibrium of the
microorganism between water and soil, and furthermore
on the soil composition. This involves the presence of
salts, organic matter, and pH. Microorganisms exist in a
state of zero charge when the pH reaches a characteristic
value called the Isoelectric point (pI), and this value
varies for each microorganism. Microorganisms with
high pI tend to absorb to surfaces to a higher extent
than those with low pI. The pI of phage MS2 (pI 3.9) is
similar to the pI of hepatitis A (pI 2.8), and lower than
the value for poliovirus-1 (pI 7.2). Studies performed in
1995 (Sobsey, Hall, and Hazard 1995) demonstrated that
absorption of poliovirus-1 to soil columns was higher
than MS2 and hepatitis A. The pI of NV (HuNoV GI)
determined from VLPs produced in the laboratory
was estimated to be 4.9 (Redman et al. 1997). Based on
this value, NV is expected to be more absorptive than
MS2, but less so than poliovirus-1. The study performed
by Meschke and Sobsey (1998) on the absorption of
NV, poliovirus-1, and phage MS2 in six different soils
confirmed that NV is less absorptive than poliovirus-1,
suggesting that it will be easier to remove NV than
poliovirus-1 from sediments. Prediction of absorptive
properties based on pI values refers to overall virus
charge under a given pH, but not to local areas of charge
of the virion. Therefore, as demonstrated by Redman and
colleagues (1997) for MS2 and NV-VLPs, depending on
the pH of the environment, viruses with higher pI may
display less absorption than viruses with lower pI.
It is generally accepted that very low or very high
pH may decrease pathogen viability. In the case of NoVs,
however, it has been demonstrated that pH lower than 3
or higher than 10 will not affect virus stability (Duizer et
al. 2004). Moreover, evidence suggests that adsorption
of viruses to particulate matter and sediments confers
protection against the inactivating influences of pH.
Solar radiation promotes inactivation of viruses
through visible and shortwave UV components. Again,
lab-scale experiments showed that although differences
exist between UV inactivation of surrogates of NoVs
(FeCV and CaCV) in suspensions or on a dried surface,
inactivation also is achieved in the presence of high
organic material because RNA is the target. If UV
is compared with ionizing radiation such as gamma
rays, the former is more effective in the presence of
solutes that can react with free OH radicals (De Roda
Husman et al. 2004). But in contrast to studies of water
sanitation, the effects of these radiations have not been
studied extensively for animal manure.