1 INTRODUCTION
Avian reovirus (ARV) has caused immense economic problems in the chicken, duck, goose, and turkey industries worldwide (Palya et al., 2003, Rosa et al., 2014). Waterfowl reoviruses (WRVs) have been associated with various disease conditions in ducks and geese of different species, including Muscovy duck white spot disease caused by classical Muscovy duck reovirus (MDRV) (Yun et al., 2013, Farkas et al., 2014, Kuntz-Simon et al., 2002, Le Gall-Recul et al., 1999, Gaudry et al., 1972), duck hemorrhagic necrotizing hepatitis, and spleen necrosis disease in ducks caused by the novel Muscovy duck reovirus (N-MDRV) (Yun et al., 2014, Li et al., 2016, Zhang et al., 2019) and the novel Duck reovirus (NDRV) (Liu et al., 2011, Chen et al., 2012b, Yun et al., 2014, Zhu et al., 2015, Wang et al., 2020c, Zhang et al., 2019, Luo et al., 2021), spleen and liver inflammation in geese caused by goose reovirus (GRV) (Wang et al., 2013, Palya et al., 2003, Yun et al., 2013), hemorrhagic necrotic hepatitis caused by the new type of goose reovirus (N-GRV) (Wang et al. 2002; Yun et al., 2012). It has been reported that WRVs can be classified into two genotypes(Wang et al., 2013). Genotype 1 comprises MDRV and GRV. While genotype 2 comprises NDRV, N-MDRV, and N-GRV (Wang et al., 2013).
The ARV genome includes ten segments that can be separated into three classes based on their sizes: large (L1, L2, L3), middle (M1, M2, M3), and small (S1, S2, S3, S4). The S1 segment is the only tricistronic gene that encodes P10, P18, and σC proteins (Zhu et al., 2015, Benavente and Martínez-Costas, 2007). The outer capsid proteins σC, σB, and μB of ARV are considerably variable, whereas the inner capsid proteins are relatively conservative (Benavente and Martínez-Costas, 2007). Additionally, σC proteins play an essential role in viral fusion, invasion, neutralizing antibody induction, and pathogenicity (Du et al., 2020, Ma et al., 2012, Shih et al., 2004, Benavente and Martínez-Costas, 2007). Meanwhile, σC is regarded as the most variable protein of all the ARV proteins (Benavente and Martínez-Costas, 2007). σC gene was usually used for epidemiological studies and viral classification of ARVs (Luo et al., 2021, Palomino-Tapia et al., 2018).
In recent years, many NDRV outbreaks emerged in China (Wang et al., 2019, Wang et al., 2020a, Cao et al., 2019, Zhang et al., 2019). However, few studies have performed the evolutionary status analysis on NDRV in central China. In this study, we isolated two NDRV strains from different duck farms in Henan province, central China. To better understand the molecular characteristics of the NDRVs circulating in duck populations, the σC genes of both isolates were cloned, sequenced, and their phylogeny and mutations were analyzed. This study systematically describes the genetic and evolutionary characteristics of the ongoing NDRV strains and highlights that continuous surveillance is needed to develop proper vaccines and reasonable control programs.