Detection and genetic characterization of porcine sapovirus from pigs
with diarrhea
Abstract
Porcine Sapovirus (SaV) was first identified by electron microscopy in
the United States in 1980 and has since been reported from both
asymptomatic and diarrheic pigs usually in mixed infection with other
enteric pathogens. SaV as the sole etiological agent of diarrhea in
naturally infected pigs has not previously been reported in the United
States. Here, we used four independent lines of evidence including
metagenomics analysis, real-time RT-PCR (rRT-PCR), histopathology, and
in situ hybridization to confirm porcine SaV genogroup III (GIII) as the
sole cause of enteritis and diarrhea in pigs. A highly sensitive and
specific rRT-PCR was established to detect porcine SaV GIII. Examination
of 184 fecal samples from the outbreak farm showed that pigs with
clinical diarrhea had significantly lower Ct values (15.9 ± 0.59)
compared to clinically unaffected pigs (35.8 ± 0.71). Further survey of
336 fecal samples from different states in the United States
demonstrated that samples from pigs with clinical diarrhea had a
comparable positive rate (45.3%) with those from non-clinical pigs
(43.1%). However, the SaV-positive pigs with clinical diarrhea had
significantly higher viral loads (Ct = 26.0 ± 0.5) than those positive
but clinically healthy pigs (Ct = 33.2 ± 0.9). Phylogenetic analysis of
20 field SaVs revealed that all belonged to SaV GIII and recombination
analysis indicated that intra-genogroup recombination occurred within
the field isolates of SaV GIII. These results suggest that porcine SaV
GIII plays an important etiologic role in swine enteritis and diarrhea
and rRT-PCR is a reliable method to detect porcine SaV. Our findings
provide significant insights to better understand the epidemiology and
pathogenicity of porcine SaV.