EU/OIE/National Reference Laboratory for Avian Influenza and Newcastle Disease, FAO Reference Centre for Animal Influenza and Newcastle Disease, Istituto Zooprofilattico Sperimentale delle Venezie, 35020 Legnaro, Italy.
National Reference Laboratory of Avian Influenza and Newcastle Disease, National Diagnostic and Research Veterinary Medical Institute, 1231 Sofia, Bulgaria.
Viruses. 2021 Oct 16;13(10):2086. doi: 10.3390/v13102086.
The first detection of a Highly Pathogenic Avian Influenza (HPAI) H5N8 virus in Bulgaria dates back to December 2016. Since then, many outbreaks caused by HPAI H5 viruses from clade 2.3.4.4B have been reported in both domestic and wild birds in different regions of the country. In this study, we characterized the complete genome of sixteen H5 viruses collected in Bulgaria between 2019 and 2021. Phylogenetic analyses revealed a persistent circulation of the H5N8 strain for four consecutive years (December 2016-June 2020) and the emergence in 2020 of a novel reassortant H5N2 subtype, likely in a duck farm. Estimation of the time to the most recent common ancestor indicates that this reassortment event may have occurred between May 2019 and January 2020. At the beginning of 2021, Bulgaria experienced a new virus introduction in the poultry sector, namely a HPAI H5N8 that had been circulating in Europe since October 2020. The periodical identification in domestic birds of H5 viruses related to the 2016 epidemic as well as a reassortant strain might indicate undetected circulation of the virus in resident wild birds or in the poultry sector. To avoid the concealed circulation and evolution of viruses, and the risk of emergence of strains with pandemic potential, the implementation of control measures is of utmost importance, particularly in duck farms where birds display no clinical signs.
保加利亚首次检测到高致病性禽流感（HPAI）H5N8 病毒可以追溯到 2016 年 12 月。自那时以来，该国不同地区的家禽和野鸟中已报告了多起由来自 clade 2.3.4.4B 的 HPAI H5 病毒引起的暴发。在本研究中，我们对 2019 年至 2021 年间在保加利亚收集的 16 株 H5 病毒的完整基因组进行了特征描述。系统进化分析显示，H5N8 株已连续四年（2016 年 12 月至 2020 年 6 月）持续传播，并于 2020 年出现了一种新的重配 H5N2 亚型，可能在一个养鸭场中出现。对最近共同祖先的时间估计表明，这种重配事件可能发生在 2019 年 5 月至 2020 年 1 月之间。2021 年初，保加利亚在家禽部门经历了新的病毒传入，即一种自 2020 年 10 月以来一直在欧洲传播的 HPAI H5N8。在家禽中周期性地发现与 2016 年流行有关的 H5 病毒以及重组毒株，这可能表明居留野生鸟类或家禽部门中存在未被检测到的病毒循环。为了避免病毒的隐匿传播和进化，以及出现具有大流行潜力的菌株的风险，实施控制措施至关重要，特别是在没有临床症状的养鸭场。
