3 years ago

Genesis and Spread of Newly Emerged Highly Pathogenic H7N9 Avian Viruses in Mainland China.

Wu, Li, Zhao, Shu, Zhu, Zeng, Liang, Chen, Huang, Wang, Liu, Shi, Bo, Dong, Zhang, Qi, Yu, Yang
The novel low pathogenic H7N9 avian influenza A viruses (LPAI H7N9) have caused a threat to public health for their high mortality and morbidity since their emergence in 2013. Recently, highly pathogenic variants of these H7N9 viruses (HPAI H7N9) have emerged and caused human infections and poultry outbreaks in Mainland China. However, it is still unclear how the HPAI H7N9 virus was generated and how it evolved and spread in China. Here, we show that the ancestor virus of the HPAI H7N9 viruses originated in the Yangtze Delta Region and spread southward to the Pearl Delta Region, possibly through live poultry trades. After introduction into the Pearl Delta Region, the origin LPAI H7N9 virus acquired four amino acid insertions in the HA protein cleavage site and mutated into the HPAI H7N9 virus in late May 2016. Afterward, the HPAI H7N9 viruses further reassorted with LPAI H7N9 or H9N2 viruses locally and generated multiple different genotypes. As of 14 July 2017, the HAPI H7N9 viruses had spread from Guangdong province to at least 12 provinces. The rapid geographical expansion and genetic evolution of the HPAI H7N9 viruses pose a great challenge, not only to public health, but also to poultry production. Effective control measures, including enhanced surveillance, are therefore urgently needed.IMPORTANCE The LPAI H7N9 virus has caused five outbreak waves in humans and was recently reported to have mutated into highly pathogenic variants. It is unknown how the HPAI H7N9 virus originated, evolved, and disseminated in China. In this study, we comprehensively analyzed the sequences of HPAI H7N9 viruses from 28 human and 21 environmental samples covering eight provinces in China that were taken from November 2016 to June 2017. The results show that the ancestor virus of the HPAI H7N9 viruses originated in the Yangtze Delta Region. However, the insertion event of four amino acids in the HA protein cleavage site of a LPAI H7N9 virus occurred in late May 2016, in the Pearl Delta Region. The mutated HPAI H7N9 virus further reassorted with LPAI H7N9 or H9N2 viruses that were co-circulating in poultry. Considering the rapid geographical expansion of the HPAI H7N9 viruses, effective control measures are urgently needed.

Publisher URL: http://doi.org/10.1128/JVI.01277-17

DOI: 10.1128/JVI.01277-17

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