Identification and molecular characterization of novel triple reassortant MRV3 and MRV2 viruses with bat, human and unidentified host MRVs in the same swine farm in Italy: evidence of undiscovered genetic diversity

Mammalian Orthoreoviruses (MRV) are segmented dsRNA viruses belonging to the Reoviridae. MRVs infect mammalian species, causing asymptomatic, respiratory, or gastro-enteric infections. MRVs are divided into 3 serotypes: MRV1, MRV2 and MRV3. In Europe MRV was first isolated in 1998 from swine in Austria and subsequently reported more than 15 years later in 2015 in Italy. Here we conducted the first molecular characterization of swine MRV2 in Italy resulting from reassortant events involving a MRV3 circulating in the same swine farm in the previous two years in North East Italy. The phylogenetic analysis revealed a considerable genetic diversity of the Italian MRV3 and MRV2 compared to other swine MRVs. Both MRVs are triple reassortant viruses presenting a similar genetic backbone with the exception of the S1, S4, M2 genes that results from reassortant events with viruses of unknown source and bat and human origin strains. The other genes form distinct genetic groups indicating a geographic related evolution of swine MRVs. This is the first report of complete molecular characterization of novel triple reassortant MRVs in Italy and Europe that suggest an enormous undiscovered genetic diversity of MRVs.