Detection of Multiple Genotypes of Calicivirus Infection in Asymptomatic Swine in Taiwan

Abstract

Noroviruses (NoVs) and sapoviruses (SaVs) of the family Caliciviridae are emerging enteric pathogens in humans and animals. Recent detection of genogroup II norovirus (GII NoV) RNA from swine raises public health concerns about zoonotic transmission of porcine NoVs to humans. However, few papers reported genotype distributions and epidemiological features in swine farms and their genetic relationship to human strains, which was the objective of our study. This study investigated the epidemiological features and genotypes of caliciviruses in swine farms using 533 pig faecal samples from six farms in central and southern Taiwan, tested for viral RNA using RT-PCR targeting the conserved polymerase gene. NoVs and SaVs were detected with a positive rate of 7.1% and 0.6%, respectively. To confirm the positive rate of NoVs, 255 pig faecal samples from two farms in central Taiwan were tested with primer pairs targeting the partial capsid gene of GII, and 32.3% of the positive rate was found. Furthermore, the results from the capsid region suggested a higher positive rate of 41.7% in winter than 26.4% in summer with statistical significance (P < 0.05). Sequence analysis showed 29 strains belonging to GII.4 (human) and nine strains belonging to GII.11 (swine) identified based on the partial polymerase gene. Additional genotypes clustered with GII.2 (human) and GII.18 (swine) were also characterized based on the partial capsid gene. SaVs detected in porcine faecal samples belonged to genogroup III (GIII), which clustered with the PEC-Cowden strain. Our study demonstrated the presence of multiple genotypes of both human and porcine NoVs infecting swine of various ages asymptomatically. Although the zoonotic potential of detected human NoVs in swine was not conclusive owing to the lack of local human faecal samples, our study revealed the importance of monitoring emerging strains in swine to mitigate the potential impact of recombinant NoVs infecting the human population.

Prevalence of Porcine Noroviruses, Molecular Characterization of Emerging Porcine Sapoviruses from Finisher Swine in the United States, and Unified Classification Scheme for Sapoviruses

“…These differences could be due to different geographical locations, different ages of pigs sampled, or the use of different detection methods and primers with various specificities. Most porcine NoVs belong to the typical porcine genotypes (GII.11, -18, and -19), but human GII NoV-like RNA (GII.2, -3, -4, and -13) was occasionally detected from pigs in Asia (8,15). Overall there was no significant prevalence difference among the disinfection treatments (biocides and water control; see Table S1 in the supplemental material).…”

“…Even though different ages of pigs were tested, NoVs were detected only in finisher pigs (7). A Canadian study reported 25% prevalence (41), and many other studies found lower prevalence rates: 2% to 4.6% in Europe (5, 42), 9% in New Zealand (43), 8% in Brazil (44), and Ͻ1% to 15% in Asia (8,15,22). These differences could be due to different geographical locations, different ages of pigs sampled, or the use of different detection methods and primers with various specificities.…”

“…4 and GII.12 NoVs can replicate in experimentally inoculated gnotobiotic piglets (13,14). Recently, human NoV-like NoV RNA has been detected in feces of commercially reared pigs, some of which were simultaneously infected with porcine NoVs (8,15). This is especially worrisome, even at low levels of infection, since recombination commonly occurs among NoVs within the same genogroup (16), and coinfections of human and porcine NoVs in pigs could potentially result in novel recombinant strains with broader host ranges.…”

“…Subclinical infections with NoVs and SaVs are common and can occur in humans as well as in pigs (1,5,6). Noroviruses have mainly been found in finisher pigs, while SaVs have been detected in all age groups of pigs (7,8).…”

Occurrence of Norovirus in pig faecal samples in the Eastern Cape, South Africa

“…Norovirus is mostly detected in finisher swine, whereas Sapovirus has been found in all different age groups of swine [10,12]. Swine illnesses are associated with porcine Sapovirus while the influence of Norovirus contagions in swine is unknown [3].…”