Highly Pathogenic Avian Influenza Clade 2.3.4.4 Subtype H5N6 Viruses Isolated from Wild Whooper Swans, Mongolia, 2020

Abstract

We identified clade 2.3.4.4 highly pathogenic avian influenza A(H5N6) viruses from whooper swans ( Cygnus cygnus ) found dead in Mongolia. The identification of these infections in wild birds in this area is of concern because of the potential for virus dissemination during fall migration.

Assessing potential pathogenicity of novel highly pathogenic avian influenza (H5N6) viruses isolated from Mongolian wild duck feces using a mouse model

“…These migration patterns and our tMRCA data of A/wildDuck/MN/H5N6/2018-19 (July to September 2018) hypothesize that these migratory waterfowl pick up H5N6 viruses during their spring migration, and carry it to their breeding ground in Mongolia where they stay between May and August. This was consistent with a previous study that suggested that the spring bird migration pattern matched with the timing and route of H5N6 virus transmission between Xinjiang and Mongolia [ 15 ]. Taken together, this data suggests that the spring migration plays a significant role in the transmission and circulation of HPAI H5N6 in Mongolia.…”

“…This result does corroborate our molecular characterization which showed that the A/wildDuck/MN/H5N6/2018-19 isolate lacked two of the individual mutations in the PB2 protein (lysine at position 627 to glutamic acid and aspartate at position 701 to asparagine) leading to low pathogenicity in mice [ 52 , 56 ]. However, the A/wildDuck/MN/H5N6/2018-19 isolate MLD 50 value (5.68-log10 EID50) was lower than the MLD 50 (6.38-log 10 EID 50 ) of the A (H5N6) Xinjiang/2020/2.3.4.4 h virus identified in China in 2020, despite its close relationship with the recently described 2020 H5N6 Mongolian isolates [ 15 , 17 ]. This suggests that the potential virulence of the A/wildDuck/MN/H5N6/2018-19 isolates are likely to be higher than the 2020 H5N6 Mongolian isolates.…”

“…Our phylogenetic analysis demonstrated that A/MN/H5N6/2018-19 belongs to subclade 2.3.4.4h, with all eight gene segments showing high degrees of identity with the (A) Xinjiang/12.24_WLMQXL/2018 like viruses (99.74%–100%). However, seven of these gene segments shared significantly lower degrees of nucleotide identity with the novel Mongolian H5N6 isolates reported in 2020 (97.46%–98.73%), the one gene that exhibits any significant similarity (99.21%) was the M gene (Appendix Table 2, see Supplemental data) [ 15 , 25 ]. These results demonstrate that our novel A/wildDuck/MN/H5N6/2018-19 and the H5N6 Mongolia 2020 isolates form two distinct genotypes.…”

“…Global surveillance data suggests that there are two dominant H5 HPAI clades 2.3.4.4b and 2.3.4.4h, in circulation across Asia, Europe and the Middle East [ 7 , 12–19 ], with seven human cases of H5N8 and five human cases of H5N6/2.3.4.4b reported in the Russian Federation and China, respectively, in 2021 [ 20 ]. Clade 2.3.4.4h viruses were also detected in wild migratory birds and humans in China, Vietnam, Mongolia and Bangladesh [ 11 , 15 , 17 , 21 ]. Remarkably, the H5N6/2.3.4.4h A/Chongqing/00013/2021 strain was isolated from a human sample in 2021 and its sequences were uploaded to the GSAID databases with GenBank ID: EPI_ISL_1081369 [ 20 ].…”

“…There were a total of eight H5 HPAIV outbreaks from clades 2.2 and 2.3.2.1, as confirmed by the Mongolian AIV surveillance programme, in Mongolia from 2005 and 2011 and there have been no cases of H5 HPAI reported in this region from 2012 and 2019 [ 22 ]. However, there were several HPAI H5N6 2.3.4.4h clade viruses isolated from wild whooper swan in Mongolia in 2020, some of which included mammalian host-specific markers [ 15 , 25 ]. However, the biological characteristics and antigenicity of these viruses have not yet been investigated.…”