Abstract
We report the full-length sequence of two chicken source influenza A (H7N9) viruses found in Guangdong live poultry market (LPM) during the most recent wave of human infections (from October 2016 to the present time). These viruses carry insertion of poly-basic amino acids (KGKRTAR/G) at the protease cleavage site of the HA protein, which were previously found in the highly pathogenic (HP) human influenza A (H7N9) [IAV(H7N9)] strains. Phylogenetic analysis of these two novel avian influenza viruses (AIVs) suggested that their genomes reassorted between the Yangtze River Delta (YRD) and Pearl River Delta (PRD) clades. Molecular clock analysis indicated that they emerged several months before the HP human strains. Collectively, our results suggest that IAV(H7N9) viruses evolve in chickens through antigenic drift to include a signature HP sequence in the HA gene, which highlights challenges in risk assessment and public health management of IAV(H7N9) infections at the human-animal interface.
Highlights
From March 2013 to March 2017, annual epidemics of IAV(H7N9) in China resulted in 1,329 human infections as reported to the World Health Organization (WHO) by the National Health and Family Planning Commission of China and other regional sources[1, 2]
Our phylogenetic analysis has shown that these novel avian viruses are reassortants of the two distinct genetic lineages of the Yangtze River Delta (YRD) and Pearl River Delta (PRD) clades and that their HA proteins contain the KGKRTAR/G motif with insertion of poly-basic amino acids at the HA cleavage site, which has previously been shown to be among the sequences of highly pathogenic (HP) human influenza virus strains
Since we only collected samples from one live poultry market (LPM), this finding does not necessarily represent the entire situation of the ongoing 5th epidemic of influenza virus infections in China, but it still reveals a potential threat on public health
Summary
From March 2013 to March 2017, annual epidemics of IAV(H7N9) in China resulted in 1,329 human infections as reported to the World Health Organization (WHO) by the National Health and Family Planning Commission of China and other regional sources[1, 2]. During the ongoing fifth wave, 460 human IAV(H7N9) infections have been reported, including 453 in mainland China; six associated with travel to mainland China from Hong Kong (four cases), Macao (one) and Taiwan (one); and one in an asymptomatic poultry worker in Macao[1]. Human samples recently reported from the fifth epidemic contain the KRKRTAR/G or KGKRIAR/G motif with insertion of multiple basic amino acids in the HA cleavage site that is characteristic of HP avian influenza (HPAI) viruses[5, 8, 9]. Our phylogenetic analysis has shown that these novel avian viruses are reassortants of the two distinct genetic lineages of the YRD and PRD clades and that their HA proteins contain the KGKRTAR/G motif with insertion of poly-basic amino acids at the HA cleavage site, which has previously been shown to be among the sequences of HP human influenza virus strains. We propose that this HA sequence change observed in the novel AIVs in our study might serve as a potential precursor to those found in HP human H7N9 viruses
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