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
and Borgsteede observed enhanced survival of A.
suum eggs under anaerobic conditions compared with
untreated slurry—reporting 80% viability after 12 wk
(Gaasenbeek and Borgsteede 1998). Juris and colleagues
had similar results, reporting more than 80% viability
of eggs after 20 d of anaerobic stabilization (Juris et al.
1996) in tanks designed to simulate anaerobic lagoon
stabilization. The effectiveness of ensiling the solid
fraction of separated swine manure was examined by
Caballero-Hernandez and colleagues as an alternative
technology that might decrease the infectivity of A.
suum eggs (Caballero-Hernández et al. 2004). Ensiling
of manure had no effect on the observed egg count, and
nearly 70% of recovered eggs remained viable after 56 d
of treatment.
To examine the possibility of environmental
transport after land application of swine manure, egg
survival in swine slurries land-applied on outdoor
plots under varying conditions of sun and simulated
rainfall was assessed (Gaasenbeek and Borgsteede 1998).
Eggs were collected from naturally infected pigs at a
slaughterhouse in the Netherlands and inoculated into
tubes containing pig slurry. Tubes were placed on 1m2
plots and treated to artificial rainfall that reflected the
long-range average for the country. Survival of parasite
eggs was highest on wet, shaded plots, with at least 90%
egg viability at 8 wk. On sunny (temperature did not
exceed 25°C), dry plots, egg survival was lowest, and a
90% loss of viability was observed between 2 and 8 wk.
This study also found that increased relative humidity
(77.5% and 100%) during the experiment favored egg
survival. The study did not provide specific data on
rainfall parameters or specific conditions of shade or
sun, so it is unknown which part of the United States is
most represented by the experimental conditions of the
study. A study in Norway found that viable eggs could
be recovered from soils amended with sewage sludge for
more than 810 d (Bürger 1982). Application of untreated
swine slurries to soil revealed that A. suum eggs
remained in the most superficial layers of the soil column
and were vulnerable to runoff (Papajova et al. 2002).
A. suum egg survival characteristics in untreated
slurries and in anaerobic lagoons suggest that a
significant proportion of excreted viable eggs may
be land-applied on farms using this management
practice to dispose of manure and utilize manure
nutrients. Once in the field, eggs may remain on the
superficial layers and on vegetation for several weeks.
Furthermore, during periods of rainfall, and the
greatest potential for runoff, egg survival is greatest.
Most research on this subject has been done in Europe,
however, so it is unknown how this compares to
conditions in the United States.
cr y p t o s p o r i d i u m
Cryptosporidium describes a genus of protozoan
parasites that infect a wide range of vertebrates. There
are several Cryptosporidium species, most of which
are host-adapted, but there are zoonotic strains of C.
parvum that are associated with outbreaks in several
mammalian hosts. Cryptosporidium is an intracellular
parasite that typically infects epithelial cells of the small
intestine. But infection sites outside the intestinal tract
can occur. The life cycle is direct, meaning a period
of development outside the host is not required and
oocysts are infective immediately when passed from
infected hosts. Autoinfections also can occur (Fayer
1997). Fewer than ten oocysts may be sufficient to
initiate infection in susceptible hosts (Caccio et al. 2005;
Okhuysen et al. 2002).
Cryptosporidium sp. are transmitted via
contaminated feed and water. Opportunities for
human infection exist during exposure to infected
livestock, their manure, or contaminated water.
Oocysts are environmentally stable; consequently,
fecal contamination of the environment can result in
waterborne dissemination of oocysts and in human
outbreaks associated with drinking and recreational
waters. Cryptosporidiosis is a common cause of
protozoal diarrhea in humans worldwide. In 1993,
Cryptosporidium was responsible for the largest
waterborne disease outbreak in the United States
since monitoring began. Although a livestock source
was suspected initially, molecular analysis of isolates
revealed homology with a human strain (Caccio et al.
2005; Zhou et al. 2003).
Cryptosporidiosis is reported in swine. Although
diarrhea has been the primary clinical sign, many
infected pigs have concurrent infections with other