Sequence and phylogenetic analysis of H10 subtypes
Two H10N4 strains (JDS120613-H10N4 and JDS120662-H10N4) were isolated from Common teal(Anas crecca )and Mallard (Anas platyrhynchos ) at Jiuduansha Natural Reservation Zone in 2018. Except for one polymerase acidic (PA) gene, the whole genome sequences of the two strains were obtained, and the sequence homology analysis showed that they shared 92.9% to 99.3% nucleotide sequence identity among the seven gene segments. A BLAST search (https://blast.ncbi.nlm.nih.gov/Blast.cgi ) revealed that the two hemagglutinin (HA) genes of these H10N4 strains were most closely related to that of A/duck/Mongolia/709/2015(H10N7), while their neuraminidase (NA) genes were highly related to those genes in A/duck/Mongolia/258/2011(H8N4) and A/garganey/Bangladesh/38920/2019(H7N4). The matrix (M) gene of JDS120662-H10N4 had the most similarity with H6N2 virus isolated in Hubei, and the other internal genes of the two H10N4 strains shared most (>98.36%) similarities with H10, H7, H11, H8, H12 and H3 subtypes isolated in Hokkaido, Mongolia, Egypt, Bangladesh, Georgia and Tottori (Table 2).
In the phylogenetic trees, the HA and NA genes of JDS120613-H10N4 and JDS120662-H10N4 strains were grouped together and clustered in the Eurasian Lineage. The HA genes showed a close relationship with the H10N7 strains circulating in ducks in Cambodia and Mongolia, and NA genes were associated with H7N4 and H8N4 viruses isolated in garganey and ducks in Bangladesh (Figure 1). PB1 polymerase (PB1) and M genes of the two H10N4 strains were all grouped together in a small sublineage, and were closely related to H3N2, H5N2 and H6N2 viruses circulating in Japan and China. Nucleoprotein(NP)gene of JDS120662-H10N4 was closed to H7N7 and H7N1 viruses isolated from Tottori and South Korea, and the NP gene of JDS120613-H10N4 was clustered with them in a small group. PB2 polymerase (PB2) and nonstructural (NS) genes of the two strains were all clustered in two different groups and were genetically close to those of viruses isolated from ducks circulating in Tomsk, Mongolia, Japan, Bangladesh and China located along the Eurasian-Australian Migration Flyway (Figure S1).