Laboratory of Microbiology, Faculty of Veterinary Medicine, Hokkaido University, Kita-18 Nishi-9, Kitaku, Sapporo, Hokkaido 060-0818, Japan.
Laboratory of Microbiology, Faculty of Veterinary Medicine, Hokkaido University, Kita-18 Nishi-9, Kitaku, Sapporo, Hokkaido 060-0818, Japan; Department of Veterinary Medicine, College of Agriculture, Can Tho University, Can Tho 900000, Viet Nam.
Infect Genet Evol. 2020 Mar;78:104117. doi: 10.1016/j.meegid.2019.104117. Epub 2019 Nov 21.
During the annual surveillance of avian influenza viruses (AIVs) in Vietnam in 2018, three H7N7 AIV isolates were identified in domestic ducks in a single flock in Vinh Long province. The present study is the first documented report of H7N7 virus isolates in Vietnam and aimed to characterize these viruses, both genetically and antigenically. Deduced amino acid sequences for the hemagglutinins (HAs) indicated a low pathogenicity of these viruses in chickens. Phylogenetic analysis revealed that the H7 HA genes of these isolates were closely related to each other and belonged to the European-Asian sublineage, together with those of H7N3 viruses isolated from ducks in Cambodia during 2017. They were not genetically related to those of Chinese H7N9 or H7N1 viruses that were previously detected in Vietnam during 2012. Interestingly, the M genes of the two H7N7 virus isolates were phylogenetically classified into distinct groups, suggesting an ongoing reassortment event in domestic ducks because they were isolated from the same flock. These H7N7 viruses exhibited somewhat different antigenic characteristics compared with other representative H7 low pathogenic AIVs. Surprisingly, the antigenicity of Vietnamese H7N7 viruses is similar to Chinese H7N9 highly pathogenic AIV. The findings of this study suggest that H7N7 viruses may be undergoing reassortment and antigenic diversification in poultry flocks in Vietnam. The silent spread of Vietnamese H7N7 viruses in chickens may lead to acquire high pathogenicity in chickens although the zoonotic potential of the viruses seems to be low since these viruses retain typical avian-specific motifs in the receptor-binding site in the HA and there is no mutation related to mammalian adaptation in PB2 gene. Thus, these results highlight the need for continuous and intensive surveillance of avian influenza in Vietnam, targeting not only highly pathogenic AIVs but also low pathogenic viruses.
在 2018 年越南对禽流感病毒（AIV）的年度监测中，在同一家禽养殖场的家鸭中鉴定出了三株 H7N7 AIV 分离株。本研究首次记录了越南 H7N7 病毒分离株，并旨在对这些病毒进行遗传和抗原特征分析。血凝素（HA）的推导氨基酸序列表明这些病毒对鸡的低致病性。系统进化分析显示，这些分离株的 H7 HA 基因彼此密切相关，属于欧亚亚系，与 2017 年柬埔寨从鸭中分离的 H7N3 病毒有关。它们与之前在 2012 年越南检测到的中国 H7N9 或 H7N1 病毒没有遗传关系。有趣的是，两株 H7N7 病毒的 M 基因在系统进化上被分为不同的组，这表明在家禽中正在发生持续的重配事件，因为它们是从同一养殖场分离出来的。与其他代表性的低致病性 AIV 相比，这些 H7N7 病毒表现出不同的抗原特征。令人惊讶的是，越南 H7N7 病毒的抗原性与中国 H7N9 高致病性 AIV 相似。本研究结果表明，H7N7 病毒可能在家禽养殖场中发生重配和抗原多样化。越南 H7N7 病毒在家禽中的隐匿传播可能导致其获得高致病性，尽管这些病毒的人畜共患潜力似乎较低，因为这些病毒在 HA 的受体结合位点保留了典型的禽特异性基序，并且在 PB2 基因中没有与哺乳动物适应相关的突变。因此，这些结果强调了越南需要对禽流感进行持续和强化监测，不仅要针对高致病性 AIV，还要针对低致病性病毒。
