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
the time required for a 1-log reduction in oocysts ranged
from 133 to 345 d in summer and 217 to 270 d in winter
(Hutchison 2005c). This is considerably longer than
the previous persistence estimates of 28 d in manure at
20–37°C and more than 12 wk in frozen manure (Olson
et al. 1999). Cryptosporidium oocysts have been shown
to attach readily to solid particles, with 30% attaching
instantaneously to particles in secondary human sewage
effluent and 75% attaching after 24 hr (Ferguson et al.
2003). How this compares with swine lagoon effluent
is unknown, however, because treatment processes
of human sewage are different from swine manure
management systems.
Rainfall has been shown to be a significant
factor in the release and environmental transport
of waste-associated oocysts. With the application of
Cryptosporidium oocysts to soil blocks followed by
intermittent irrigation under laboratory conditions,
researchers have found that oocysts can move through
some soils for more than 70 d, and most oocysts
remained in the upper 2 cm of the soil block (Fayer
2000). In a field trial, land application of lagoon
wastewaters to 1.5-m 2 plots followed by simulated
rainfall and collection of runoff waters resulted in the
recovery of up to 2.2 x 10 6 oocysts (Thurston-Enriquez,
Gilley, and Eghball 2005). Subsurface flow wetland
treatment of manure reportedly reduces C. parvum
oocysts 1.0–3.1 log10 per meter (m) of vegetated buffer
(Ferguson et al. 2003). If runoff of oocysts from land
application fields results in water contamination,
oocysts survive in water up to 10 wk at 20–30°C and
more than 12 wk in frozen water at 4°C.
GiArdiA intestinAlis
Giardia describes a genus of flagellate protozoan
parasites of the small intestine that infects a wide range
of vertebrates. There are three main species described:
Giardia angilis, Giardia muris, and Giardia intestinalis
(Eligio-Garcίa and Cortes-Campos 2005). Giardia
intestinalis also is known as Giardia duodenalis and
Giardia lamblia and is the species known to infect
humans (Ali and Hill 2003; Eligio-Garcίa and Cortes-
Campos 2005). The life cycle of Giardia is direct,
meaning cysts of Giardia are infective immediately when
excreted by infected hosts. The life cycle is short; cysts
appear in the feces within a week or two after infection
in dogs, where the life cycle is better understood than in
swine (Bowman, Lynn, and Georgi 1999).
Giardia sp. are known to infect both young and
adult swine. A Canadian survey reported that four of
six swine confinement farms were positive for Giardia,
with an overall prevalence rate of 3% in young animals
and 18% in adult swine (Olson et al. 1997). This study
used only one sample point; thus the prevalence reported
likely is underestimated because excretion of parasite
stages from infected hosts can be intermittent. In
Ohio, Giardia infections were detected in both weaned
and nursing pigs (Xiao, Herd, and Bowman 1994).
Giardia prevalence on farms varies depending on the
stage of production. For example, a Canadian study
detected Giardia in 3.8 and 9.8% of piglets and weaners,
respectively, in 10.8% of growers but 15% of finishers, and
5.7% and 4.1% of boars and sows, respectively (Olsen et
al. 2000). Control and prevention of both Giardia and
Cryptosporidium infections in pigs are complicated by the
short life cycle, long survival time of the infective stage in
the environment, and the potential for rapid reinfection
in contaminated housing of confined livestock.
Transmission between animal and human hosts
typically occurs through ingestion of fecally contaminated
water, which can come from a variety of mammalian
fecal sources. Giardiais is a common cause of protozoal
diarrhea in humans worldwide, infecting approximately
2.8 million people annually (Ali and Hill 2003).
Epidemiology
Recent progress in the molecular biology of
Giardia intestinalis has shed considerable light on the
epidemiology of this protozoal pathogen. Although
several classification schemes have been described,
the most commonly used molecular classification of
G. intestinalis is the designation of seven assemblages,
A–G, that can be distinguished by the ribosomal
ribonucleic acid and elongation factor 1 alpha genes (Ali
and Hill 2003; Eligio-García and Cortes-Campos 2005).
Only G. intestinalis assemblages A and B have been
associated with human infections and are considered
zoonotic (Ali and Hill 2003), but two distinct clusters
have been characterized in assemblage A—A-I and