Reassortment of newly emergent clade 2.3.4.4b A(H5N1) highly pathogenic avian influenza A viruses in Bangladesh

Avian influenza active surveillance was conducted in Bangladesh from January 2022 to November 2023 in live-poultry markets (LPMs) and Tanguar Haor wetlands. The predominant viruses circulating in LPMs were low pathogenic avian influenza (LPAI) A(H9N2) and clade 2.3.2.1a highly pathogenic avian influenza (HPAI) A(H5N1) viruses. Non-H9N2 LPAIs were found at Tanguar Haor and at a lower prevalence in LPMs. Starting from June 2023, we detected novel genotypes of clade 2.3.4.4b A(H5N1) viruses from ducks in LPMs. The HA, NA, and M genes of these viruses are related to those of 2020 European clade 2.3.4.4b H5N1 viruses such as A/Eurasian Wigeon/Netherlands/1/2020 (Netherlands/1). However, analyses of the other five gene segments’ sequences identified three distinct genotypes (BD-G2, BD-G3, and BD-G4). BD-G2 viruses were closely related to the clade 2.3.4.4b H5N1 viruses that have been detected in Japan and nearby regions since November 2022. BD-G3 viruses were reassortants, with gene segments from other Eurasian LPAI viruses. BD-G4 viruses were similar to BD-G2 viruses, but their NS gene was accrued from contemporary Bangladeshi clade 2.3.2.1a A(H5N1) viruses. The ability of any of the clade 2.3.4.4b viruses to displace the long-entrenched 2.3.2.1a A(H5N1) viruses in Bangladesh is unknown.

2022年1月至2023年11月，研究团队在孟加拉国的活禽市场（live-poultry markets, LPMs）以及坦瓜尔豪尔湿地（Tanguar Haor wetlands）开展了禽流感主动监测工作。活禽市场中流行的主要病毒为低致病性禽流感（low pathogenic avian influenza, LPAI）A(H9N2)亚型以及2.3.2.1a分支的高致病性禽流感（highly pathogenic avian influenza, HPAI）A(H5N1)亚型病毒。非H9N2亚型的低致病性禽流感病毒在坦瓜尔豪尔湿地被检出，且在活禽市场中的检出率较低。2023年6月起，研究团队从活禽市场的鸭只体内检测到新型2.3.4.4b分支A(H5N1)亚型禽流感病毒。该类病毒的血凝素（Hemagglutinin, HA）、神经氨酸酶（Neuraminidase, NA）以及基质蛋白（Matrix, M）基因，与2020年欧洲2.3.4.4b分支H5N1病毒（如A/Eurasian Wigeon/Netherlands/1/2020，即Netherlands/1）的对应基因具有亲缘关系。不过对其余5个基因片段的序列分析显示，该类病毒存在3种不同的基因型：BD-G2、BD-G3与BD-G4。其中BD-G2毒株与2022年11月以来在日本及周边地区检出的2.3.4.4b分支H5N1病毒亲缘关系密切。BD-G3毒株为重配病毒，其基因片段来源于其他欧亚大陆低致病性禽流感病毒。BD-G4毒株与BD-G2毒株相似，但其非结构蛋白（Non-structural protein, NS）基因来源于同期孟加拉国流行的2.3.2.1a分支A(H5N1)病毒。目前尚不清楚上述任意一种2.3.4.4b分支病毒，能否取代孟加拉国境内长期流行的2.3.2.1a分支A(H5N1)病毒。