Unrevealed genetic diversity of GII Norovirus in the swine population of North East Italy

Noroviruses (NoVs) are one of the major causative agents of non-bacterial gastroenteritis in humans worldwide. NoVs, belonging to Caliciviridae, are classified into ten genogroups (G) and eight P-groups based on major capsid protein (VP1) and of the RNA-dependent-RNA-polymerase (RdRp), respectively. In swine, the main genogroup and P-group identified are GII and GII.P; which can infect humans too. To date, only one case of GIIP.11 have been identified in swine in Italy while the circulation of other P-types is currently unknown. In the present study, 225 swine faecal samples were collected from 74 swine herds in Veneto region through on-farm monitoring. NoV circulation was particularly high in older pigs. The phylogenetic analysis showed the co-circulation of NoVs belonging to two different P-types: GII.P11 and GII.P18, here described for the first time in Italy, presenting an extensive genetic diversity, never described before worldwide. Distinct NoV genetic subgroups and unique amino acid mutations were identified for each P-type for the first time. This study demonstrated the co-circulation of diverse swine NoVs subgroups in Italy, raising questions on the origin of such diversity and suggesting that continuous monitoring of swine NoVs is needed to track the emergence of potentially zoonotic viruses by recombination events.