The novel H10N3 avian influenza virus acquired airborne transmission among chickens: an increasing threat to public health.

Following two human infections with the H10N3 avian influenza virus (AIV) in 2021 and 2022, a third case was discovered in Yunnan, China, in 2024, raising concerns about the potential for future pandemics. Recent studies have indicated that novel H10N3 viruses are highly pathogenic in mice and can be transmitted between guinea pigs via respiratory droplets without prior adaptation. However, the biological characteristics of novel H10N3 in poultry have not been fully elucidated. Our findings revealed that H10 subtype AIVs are predominantly prevalent in waterfowl. Notably, H10N8 and H10N3 viruses that have infected humans were primarily isolated from chickens. For the first time, double basic hemagglutinin cleavage sites (motif PEIKQGR↓GL) were identified in novel H10N3 AIVs, which exhibit enhanced replication in chickens, and can be transmitted between chickens through direct contact and respiratory droplets. Animal experimental studies demonstrated that ducks are also susceptible to H10N3 viruses and that the virus is transmissible through direct contact, suggesting a greater risk of transmission and recombination. Serological studies conducted among poultry workers suggest that while the human population was largely naïve to H10N3 infection, sporadic and undetected human infections did occur, indicating a potential increasing trend. These data further emphasize the growing threat to public health posed by zoonotic H10N3 subtype AIVs.IMPORTANCEExposure to poultry in live poultry markets (LPMs) is strongly associated with human infection with avian influenza viruses (AIVs), with chickens being the most common species found in these markets in China. The prevalence of AIVs in chickens, therefore, increases the risk of human infection. Notably, the main host of the novel H10N3 virus has shifted from waterfowl to chickens, and the virus can be transmitted between chickens via respiratory droplets, posing a potential risk of a pandemic within poultry populations. The novel H10N3 virus also remains sensitive to ducks and can be transmitted through direct contact, which means a greater risk of transmission and recombination. Significantly, the human population remains largely naïve to H10N3 infection, but sporadic seropositivity among poultry workers indicates previous exposure to H10 subtype AIVs. Therefore, a comprehensive surveillance of the novel H10N3 viruses in poultry is imperative. Effective control of the virus within poultry populations could significantly reduce the risk of emerging human infections.