Infectious Diseases 2023

Waterfowl globally have a high prevalence of Avian influenza viruses (AIVs) of subtype H3, which generally do not cause apparent illness in birds. However, H3 AIVs can transmit across species, as evidenced by past epidemics in horses, dogs, seals, and pigs. In April 2022, a 4-year-old boy in Henan Province, China, became the first human infected with AIV (H3N8) from his family's chickens and silky fowls. A second case was identified in May 2022, in a 5-year-old boy who had visited a live poultry market (LPM) in Hunan Province, China, and exhibited mild symptoms. A third case was reported in Guangdong Province in February 2023, where a 56-year-old female who had exposure to live poultry before falling ill died in March 2023.
The evolution of AIV subtype H3 in China, along with these human infections, underscores the threat to public health. Researchers in China conducted surveillance of poultry-associated environments from 2009 to 2022 and isolated and sequenced 188 H3 AIVs, identifying four sublineages established in domestic ducks via multiple introductions from wild birds from Eurasia. Large-scale sequence analysis of publicly available data identified 126 distinct genotypes, with the H3N2 G23 genotype currently predominating. Before February 2021, H3N8 G25 viruses that spilled over from birds to humans might have arisen from reassortment between H3N2 G23, wild bird H3N8, and poultry H9N2. H3 AIVs sometimes exhibit mammal-adapted and drug-resistance substitutions, indicating the need for ongoing surveillance and risk assessment to prepare for potential pandemics.