Source of deadly H7N9 influenza virus confirmed as from live China poultry market
Beijing: In March 2013, a novel H7N9 influenza virus was identified in China as the etiological agent of a flu-like disease in humans, resulting in some deaths.
A group of scientists, led by Professor Chen Hualan (National Avian Influenza Reference Laboratory, State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences) have investigated the origins of this novel H7N9 influenza virus.
Following analysis of H7N9 influenza viruses collected from live poultry markets, it was found that these viruses circulating among birds were responsible for human infections.
These novel H7N9 viruses are reassortants in which the six internal genes were derived from avian H9N2 viruses; however the origins of their hemagglutinin (HA) and neuraminidase (NA) genes were unclear.
A total of 970 samples were collected from live poultry markets and poultry farms located in Shanghai and Anhui Province.
Samples analyzed included drinking water, feces, contaminated soil, and cloacal and tracheal swabs. Of these samples, 20 were positive for the presence of H7N9 influenza viruses.
All of the positive samples originated from live poultry markets in Shanghai. Of these 20 positive samples, 10 were isolated from chickens, 3 from pigeons, and 7 were from environmental samples.
The complete genome of three H7N9 isolates, from a chicken, pigeon, and environmental sample, was sequenced and deposited into the GISAID database.
Genetic analysis of these isolates revealed high homology across all eight gene segments. Phylogenetic analysis of these novel H7N9 influenza virus isolates showed that that the six internal genes were derived from avian H9N2 viruses, but the ancestor of their HA and NA genes is unknown.
It is clear that the novel H7N9 viruses are the product of gene reassortment, with the internal genes from one donor, and HA and NA genes from one or several other donors.
This finding implies that H7N9 viruses have partially acquired human receptor-binding specificity. All of the H7N9 human isolates examined contained a lysine residue at position 627 in the PB2 protein.
It is well known that this lysine residue contributes to the replication and transmission of avian influenza viruses in mammalian hosts.
It is likely that the acquisition of this lysine in H7N9 viruses during their replication in human hosts has significantly contributed to their virulence and lethality in humans.