BackgroundTwo human cases of avian influenza A (H3N8) virus infection were reported in China in 2022.AimTo characterise H3N8 viruses circulating in China in September 2021-May 2022.MethodsWe sampled poultry and poultry-related environments in 25 Chinese provinces. After isolating H3N8 viruses, whole genome sequences were obtained for molecular and phylogenetic analyses. The specificity of H3N8 viruses towards human or avian receptors was assessed in vitro. Their ability to replicate in chicken and mice, and to transmit between guinea pigs was also investigated.ResultsIn total, 98 H3N8 avian influenza virus isolates were retrieved from 38,639 samples; genetic analysis of 31 representative isolates revealed 17 genotypes. Viruses belonging to 10 of these genotypes had six internal genes originating from influenza A (H9N2) viruses. These reassorted viruses could be found in live poultry markets and comprised the strains responsible for the two human infections. A subset of nine H3N8 viruses (including six reassorted) that replicated efficiently in mice bound to both avian-type and human-type receptors in vitro. Three reassorted viruses were shed by chickens for up to 9 days, replicating efficiently in their upper respiratory tract. Five reassorted viruses tested on guinea pigs were transmissible among these by respiratory droplets.ConclusionAvian H3N8 viruses with H9N2 virus internal genes, causing two human infections, occurred in live poultry markets in China. The low pathogenicity of H3N8 viruses in poultry allows their continuous circulation with potential for reassortment. Careful monitoring of spill-over infections in humans is important to strengthen early-warning systems and maintain influenza pandemic preparedness.
Avian influenza virusGuinea pigH3N8, evolutiontransmissionInfluenza A Virus, H3N8 SubtypeInfluenza A Virus, H9N2 SubtypeInfluenza in BirdsInfluenza, HumanPoultry DiseasesAnimalsChickensChinaGuinea PigsHumansMicePhylogenyPoultry
Structured evidence records
Evidence records
9 total
Host Range Experiment3 records
Host Range ExperimentExtraction confidence 0.90
Key finding
H3N8 avian influenza viruses replicated efficiently in mice and showed dual binding to avian- and human-type receptors, indicating expanded host adaptability.
A subset of nine H3N8 viruses (including six reassorted) that replicated efficiently in mice bound to both avian-type and human-type receptors in vitro.
Method
replication assay; receptor-binding assay
Experimental system
in vivo animal experiment
Host Range ExperimentExtraction confidence 0.90
Key finding
Reassorted H3N8 viruses replicated efficiently in chicken upper respiratory tract and were shed for several days, demonstrating active infection in poultry.
Whole-genome and phylogenetic analyses revealed multiple H3N8 genotypes in Chinese poultry, with reassortment introducing H9N2 internal genes into 10 genotypes associated with zoonotic human cases.
After isolating H3N8 viruses, whole genome sequences were obtained for molecular and phylogenetic analyses. Genetic analysis of 31 representative isolates revealed 17 genotypes. Viruses belonging to 10 of these genotypes had six internal genes originating from influenza A (H9N2) viruses.
A subset of nine H3N8 viruses (including six reassorted) that replicated efficiently in mice bound to both avian-type and human-type receptors in vitro.
Method
in vitro receptor binding assay
Receptors
avian-type and human-type receptors
Recombination Or Reassortment1 records
Recombination Or ReassortmentExtraction confidence 0.95
Key finding
Reassorted avian influenza A(H3N8) viruses carrying six internal genes from A(H9N2) were detected in Chinese live poultry markets and caused two human infections.
Genetic analysis of 31 representative isolates revealed 17 genotypes. Viruses belonging to 10 of these genotypes had six internal genes originating from influenza A (H9N2) viruses. These reassorted viruses could be found in live poultry markets and comprised the strains responsible for the two human infections.
Event type
reassortment
Genes or segments
six internal genes
Spillover Event1 records
Spillover EventExtraction confidence 0.95
Key finding
Avian influenza A(H3N8) viruses circulating in poultry in China in 2021–2022 caused human infections, demonstrating animal-to-human spillover from poultry to humans.
Two human cases of avian influenza A (H3N8) virus infection were reported in China in 2022... These reassorted viruses could be found in live poultry markets and comprised the strains responsible for the two human infections.
Avian influenza A (H3N8) viruses were detected through extensive surveillance of poultry and poultry-related environments in 25 provinces in China, yielding 98 isolates from 38,639 samples collected.
We sampled poultry and poultry-related environments in 25 Chinese provinces. After isolating H3N8 viruses, whole genome sequences were obtained for molecular and phylogenetic analyses. In total, 98 H3N8 avian influenza virus isolates were retrieved from 38,639 samples.
Genetic and biological characteristics of the globally circulating H5N8 avian influenza viruses and the protective efficacy offered by the poultry vaccine currently used in China
Low Polymerase Activity Attributed to PA Drives the Acquisition of the PB2 E627K Mutation of H7N9 Avian Influenza Virus in Mammals. mBio. 2019;10(3):e01162-19. 10.1128/mBio.01162-19
Emergence of a novel reassortant avian influenza virus (H10N3) in Eastern China with high pathogenicity and respiratory droplet transmissibility to mammals.
