NOROVIRUS GII IN ITALIAN SWINE POPULATION: CO-CIRCULATION OF TWO DIFFERENT GENOTYPES

Background: Noroviruses (NoVs) are responsible for 90% of viral gastroenteritis in humans. NoVs, belonging to Caliciviridae, are classified into 6 genogroups (G), further divided into 40 genotypes. NoVs identified in human gastroenteritis cases belong to GI, GII and GIV with the GII.4 being the most prevalent genotype. NoVs have been isolated from several animal species. Detection of NoV GII.4 in European pigs has raised public health concerns about the role of swine in the epidemiology of this infection. Currently, a single case of NoV in pigs is described in Italy. The present study reports preliminary data on NoV distribution and prevalence in swine in North-East Italy. Material and methods: Between March 2017 and June 2018, 207 faecal pool samples and 1922 sera from healthy pigs were collected at slaughterhouse and farms in two regions of North-East Italy: Veneto and Friuli Venezia Giulia (FVG). Eighty-three and thirty-nine farms were sampled in Veneto and FVG, respectively. A specific primer pair targeting the RdRp gene of the Calicivirus genus was used in a RTPCR screening method. NoV positive samples were subjected to sequencing for phylogenetic analysis. NoV positive samples were further characterized by full length VP1 sequencing. Phylogenetic analysis was carried out using the ML method and K2+G substitution model using PhyML 3.1. Recombinant NoV VLPs based on viral protein VP1 were generated by baculovirus expression system. The recombinant antigen was used to investigate presence of antibodies against the GII.4 in swine sera, by means of an indirect ELISA . Results: Seventy-four out of 207 (35.75%) faecal pool samples were positive for Calicivirus by RT-PCR. Twelve out of 74 (16%) samples were characterized as swine NoV by RdRp sequence analysis. According to RdRp phylogenetic analysis, 10 NoVs belong to GII.11 and 2 to GII.18. The topology of the RdRp phylogenetic tree show two distinct clusters for Italian swine GII.11, indicating the circulation of GII.11 with different genetic characteristics. Complete VP1 sequence from one sample was obtained confirming as NoV GII.11 genotype. ELISA developed on purified GII.4 VLPs indicated their reactivity with anti-NoV GII.4 human antibodies. Standardization of an ELISA test for the detection of anti GII.4 antibodies in swine sera is ongoing. Conclusions: Data presented herein show the circulation of NoVs belonging to GII.11 and GII.18 in swine population in North-East Italy. Although the presence of GII.11 in swine in Italy was reported in 2006, the present study, conducted in a different geographic area and period, by active surveillaince has allowed the detection of NoV GII.18, which has never been reported before in Italy. In addition, we report the first full-length VP1 sequence of Italian swine NoVs GII.11. NGS approach and serological studies against GII.4 NoVs are ongoing to generate additional data on NoVs in swine and eventually elucidate the role of swine for NoV infections.