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

3. Common Viruses of Swine
genotypes does not exist, a different designation has
been adopted with open numbers for P serotypes, and
numbers between brackets for P genotypes. Among
human rotavirus (HRV) strains, P1, 2, 3, 4, 5, and 11
were detected, whereas P2 and 9 were detected in pigs
(Estes and Cohen 1989; Hoshino et al. 1984; Martella et
al. 2001). Among the 22 P genotypes identified, P[4],
P[6], P[8], P[9], P[10], and P[12] are associated with
HRV, and P[6], P[7], P[14], and P[19] with pigs (Burke,
McCrae, and Desselberger 1994; Gouvea, Santos, and
Timenetsky 1994a; Huang, Nagesha, and Holmes 1993;
Kapikian, Hoshino, and Chanock 2001; Saif, Rosen,
and Parwani 1994; Yuan, Stevenson, and Saif 2006;
Zaberezhny, Lyoo, and Paul 1994). For HRV, P[4], P[6],
P[8], and P[9] correspond to serotypes P1B, P2A, P1A,
and P3, respectively, whereas in pigs, P[6] and P[7]
belong to P2B and P9, respectively (Saif, Rosen, and
Parwani 1994; Yuan, Stevenson and Saif 2006). Among
the most common human strains are P1A[8]G1, P1B[4]
G2, P1A[8]G3, and P1A[8]G4, whereas among porcine
strains, P2B[6]G4 and P9[7]G5 are the most prevalent
(Kapikian, Hoshino, and Chanock 2001; Saif, Rosen,
and Parwani 1994; Yuan, Stevenson, and Saif 2006). But
typical human and bovine G- and P genotypes have
been described in pigs that suggest the possibility of
transmission of RVs between species (Martella et al.
2001; Saif, Rosen, and Parwani 1994; Teodoroff et al.
2005; Winiarczyk et al. 2002; Yuan, Stevenson, and Saif
2006; Zaberezhny, Lyoo, and Paul 1994).
Detection
Rotaviruses can be detected in feces of infected
people or pigs by several techniques such as RT-
PCR, nested or seminested PCR, polyacrylamide
gel electrophoresis (PAGE), EM, immune electron
microscopy (IEM), immunofluorescence (IF), VI, latex
agglutination (LA), and ELISA (Iturriza-Gomara,
Green, and Gray 2000; Saif, Rosen, and Parwani 1994;
Yuan, Stevenson, and Saif 2006). During an acute RV
infection, approximately 10 8 to 10 12 viral particles/ml are
excreted. In these circumstances, diagnosis by ELISA
(sensitivity of 10 5 to 10 6 viral particles/ml) (Gilchrist
et al. 1987; Rubenstein and Miller 1982) and rapid
tests such as LA with a sensitivity of 4x10 6 up to 2x10 7
infectious particles/ml fecal suspension are useful.
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Although all these tests have shown high
specificity and sensitivity for the detection of RV in
clinical samples, in delayed sampling or environmental
samples where viruses are not replicating, the amount
of virus usually is under the detection level for these
techniques. In this scenario, molecular techniques
or techniques that combine molecular with virus
replication approaches are needed. The RT-PCR,
nested PCR, and seminested-PCR techniques have
been developed to detect RV-A, RV-B, and RV-C and
also to differentiate RV-A G- and P-types (Gouvea
et al. 1991; Gouvea, Santos, and Timenetsky 1994a, b;
Racz et al. 2000; Villena et al. 2003; Winiarczyk et
al. 2002). To compare cell culture and nested-PCR,
the presence of RV in cell culture and fecal samples
was assayed. The detection limit for virus in cell
culture supernatants was 3 x 10-2 tissue cultures
infections dose (TCID)50 by RT-PCR and 3 x 10 -3
TCID50 by nested-PCR (Elschner et al. 2002). An
immunochromatographic test for the detection of
RV-A also showed high sensitivity (89%) and specificity
(99%) compared with ELISA for feces of different
species (de Verdier Klingenberg and Esfandiari 1996).
For environmental samples, most studies have
focused on detection of RV in water as a source of
infection. The critical point in this type of sample is to
concentrate the virus, and several methods have been
assessed (Abbaszadegan, Stewart, and LeChevallier 1999;
Brassard et al. 2005; Caballero et al. 2004; Gratacap-
Cavallier et al. 2000; Hot et al. 2003; Kittigul et al. 2000;
van Zyl et al. 2004). After concentration is achieved,
detection of RV has been performed by RT-PCR,
seminested PCR, and flow cytometry (FC) (Abad, Pinto,
and Bosch 1998; Bosch et al. 2004; Fout et al. 2003; van
Zyl et al. 2004). All techniques mentioned earlier do
not differentiate between infectious or noninfectious
particles; however, this is very important to assess the risk
of disease transmission from environmental samples. In
general, the detection limit for ELISA is 10 5 particles/ml,
and RT-PCR assays detect RNA from 10 1-3 particles/ml.
Cell culture propagation has been shown to detect 10 0-1
RV infectious particles/ml, which does not differ from
RT-PCR and could be used as a substitute technique but
is more time consuming and requires maintenance of cell
lines. Detection of RNA in a sample, however, does not