Enteric calicivirus and rotavirus infections in domestic pigs

We report the prevalence of rotavirus and calicivirus infections, along with their respective association with diarrhoea in the porcine population of the region of northern Spain. A total of 221 samples were collected at random from different farms in the region and from the main slaughterhouse facility in the city of Zaragoza. Faecal samples were scored as diarrhoeic or normal and grouped into five groups to match general farm management and age criteria: group I (suckling 0-4 weeks), group II (weaning >4-8 weeks), group III (transition >8-16 weeks), group IV (fattening >16-24 weeks) and group V (adults >24 weeks). Group A rotavirus detection and caliciviruses were investigated by reverse transcription-polymerase chain reaction (RT-PCR). Conventional RT-PCR was performed using primers designed to detect rotavirus group A, caliciviruses and/or human noroviruses. A real-time RT-PCR was carried out using TaqMan probes for genogroups GI and GII of noroviruses. Rotaviruses and caliciviruses were detected with an overall prevalence of 16.7% and 12.2%, respectively. Rotavirus detection in faecal samples was associated with both age and faecal consistency, being more frequent in piglets aged <8 weeks with odds ratios (ORs) equal to 4.3 and 4.9, respectively. Calicivirus shedding in faecal samples was homogenously distributed in all ages, showing no significant association with age or faecal consistency (OR 0.87 and 0.99, respectively). A selection of rotavirus-positive stools were genotyped by multiplex nested PCR. G10, P[6], G12 P[8], G9 [p8] and G4 P[23] genotype combinations were found. Three isolates showed a G3 genotype, but their VP4 gene could not be amplified. It should be noted that the G9 genotype was the major G genotype circulating during that period in Spain. None of the porcine samples was positive for norovirus by real-time RT-PCR, despite the ability of this technique to detect at least 18 human norovirus genotypes. Our data indicate that human noroviruses are unlikely to be circulating in the porcine population; however, sapoviruses have been found. Contrary to rotavirus infection, Calicivirus infection is asymptomatic. Specific primers to detect porcine noroviruses are needed.