Detection and characterization of porcine sapoviruses from asymptomatic animals in Irish farms.

Caliciviruses are an important cause of gastroenteritis in humans and animals. Molecular analysis of the polymerase and capsid genes of porcine caliciviruses, sapoviruses (SaVs) and noroviruses (NoVs), has demonstrated a broad range of genetic diversity but information on their epidemiology and pathogenic role in pigs is limited. In this study, 292 faecal samples were obtained from 4-5 to 8-9 week old asymptomatic pigs from four porcine herds in Ireland during 2005-2007 and were screened by RT-PCR using calicivirus-specific primers. Only seven samples from two porcine herds tested positive for porcine calicivirus. By sequence analysis of the partial RNA-dependent RNA polymerase (RdRp) fragment, six samples from one such herd were closely related to each other (>98% nucleotide identity) and were characterised as genogroup (GG) III (Cowden-like) porcine SaVs. These viruses demonstrated an amino acid (aa) identity of 81.3-98.6% to GGIII SaVs. Conversely, one calicivirus strain, 9/07/Ire (identified from a different herd in 2007), was distantly related to GIII SaVs and displayed 94.6-98.6% aa identity to rare K7-like porcine caliciviruses, representatives of a potential novel SaV genogroup (GGVII), described previously in Japan and the USA. Circulation of SaVs in asymptomatic animals might be a mechanism of virus persistence in porcine populations and should be considered with respect to understanding the epidemiology of these viruses in porcine herds.