Genomic sequences and pathogenic characteristics of two variant duck reoviruses associated with spleen necrosis.

Emerging variant novel duck reovirus (NDRV) strains that cause spleen swelling and necrosis have seriously threatened the waterfowl industry since 2017. However, there is no report about the complete genomic sequence of emerging variant strains isolated from Cherry valley ducks. In this study, we acquired the complete genome sequences of two variant NDRV strains, SD19/6201 and SD19/6202, and analyzed their genetic and evolutionary relationship with other orthoreoviruses. The phylogenetic analysis of σC showed that all the Chinese NDRVs were clustered into two distinct branches. The SD19/6201 strain located in branch I with most of the Chinese NDRVs, while SD19/6202 was clustered in branch II with significantly different from the existing strains. Within the branch I, the NDRVs isolated in 2017 and thereafter clustered in a new subgroup. Comparison analysis of σC amino acid sequences indicated that ten amino acid differences were found between SD19/6201 and SD19/6202. Apart from the SD19/6201 and SD19/6202 strains, isolates in 2017 and thereafter had specific mutations at residues 132A, 138R, 158H, and 258A. These two NDRV strains showed different pathogenicity in SPF duck embryos and ducks. The viral loads in the spleen of infected ducks were significantly higher than those of other organs, which might be the reason why NDRV could cause obvious spleen necrosis in ducks. This study will help us to formulate effective prevention and control strategies against NDRV and enrich our understanding of the intra- and inter-species relationships of orthoreoviruses.