Recently, an article in your journal reported the first human case of the novel H3N8 avian influenza virus (AIV) in Henan Province, China; the same year, another case of H3N8 subtype infection was reported in Hunan Province, China. One of the two patients had acute respiratory distress syndrome, and the other had a mild condition. Moreover, the World Health Organization (WHO) reported a fatal human infection with H3N8 AIV on April 11, 2023, the first known human death caused by H3N8. The patient was a 56-year-old woman from Guangdong Province, China, who was hospitalized with severe pneumonia on March 3 and died on March 16, 2023.
As the WHO reported, nucleic acid tests of environmental samples collected from the house and live poultry markets visited by the deceased patients were positive for H3N8 AIV. Initial epidemiological investigations have indicated that exposure to live poultry markets is a likely cause of H3N8 infection. However, the exact source of the infection and how the virus relates to other H3N8 AIVs circulating among animals remains unclear. No new cases were detected among close contacts or co-exposed individuals associated with the three known cases, suggesting a low H3N8 transmission risk and limited human-to-human infectivity at this stage. H3N8 AIV is prevalent among animals worldwide and is one of the most common subtypes infecting birds. The cross-species transmission of H3N8 AIV has been reported in various mammalian species, including dogs and horses. Our previous study confirmed that H3N8 could induce adaptive mammalian mutations. AIV transmission from birds to humans is usually sporadic and occurs in specific contexts, mostly from contact with infected poultry or contaminated environments. However, owing to the widespread prevalence of this virus, more sporadic cases are expected in the future.