Poultry carrying H9N2 act as incubators for novel human avian influenza viruses

After being hit by avian influenza A H7N9 virus (134 individuals infected and 45 deaths in 2013, and 213 cases and 66 deaths as of Feb 23, 2014),1Chinese Center for Disease Control and PreventionWeekly updates human infection with avian influenza A(H7N9) virus in China.http://www.chinacdc.cn/en/Google Scholar China had their first case of fatal H10N8 infection in a human being on Dec 17, 2013, in the Jiangxi Province, which has been followed by two more cases in the same province.2Chen H Yuan H Gao R et al.Clinical and epidemiological characteristics of a fatal case of avian influenza A H10N8 virus infection: a descriptive study.Lancet. 2014; (published online Feb 5.)https://doi.org/10.1016/S0140-6736(14)60111-2Summary Full Text Full Text PDF PubMed Scopus (445) Google Scholar The two novel influenza viruses that affect human beings, H7N9 and H10N8, have similar genetic lineage: the haemagglutinin (H) gene originated from ducks and the neuraminidase (N) gene from wild birds.2Chen H Yuan H Gao R et al.Clinical and epidemiological characteristics of a fatal case of avian influenza A H10N8 virus infection: a descriptive study.Lancet. 2014; (published online Feb 5.)https://doi.org/10.1016/S0140-6736(14)60111-2Summary Full Text Full Text PDF PubMed Scopus (445) Google Scholar, 3Liu D Shi W Shi Y et al.Origin and diversity of novel avian influenza A H7N9 viruses causing human infection: phylogenetic, structural, and coalescent analyses.Lancet. 2013; 381: 1926-1932Summary Full Text Full Text PDF PubMed Scopus (465) Google Scholar Avian influenza viruses are often thought to be transmitted from wild birds to domestic birds and then to people. However, influenza viruses from wild birds could hardly ever adapt to and replicate well within domestic birds, since influenza virus from wild birds is rarely found to be prevalent in domestic hosts. Most influenza viruses from wild-bird origin would die within domestic hosts, preventing people from being infected by avian influenza virus. Both H7N9 and H10N8 viruses possess internal gene cassettes recruited from poultry H9N2 virus.2Chen H Yuan H Gao R et al.Clinical and epidemiological characteristics of a fatal case of avian influenza A H10N8 virus infection: a descriptive study.Lancet. 2014; (published online Feb 5.)https://doi.org/10.1016/S0140-6736(14)60111-2Summary Full Text Full Text PDF PubMed Scopus (445) Google Scholar, 3Liu D Shi W Shi Y et al.Origin and diversity of novel avian influenza A H7N9 viruses causing human infection: phylogenetic, structural, and coalescent analyses.Lancet. 2013; 381: 1926-1932Summary Full Text Full Text PDF PubMed Scopus (465) Google Scholar Long-term surveillance of poultry in China and east Asia shows that H9N2 virus is widely spread. Phylogenetics analyses suggest that different subtypes of avian influenza viruses cocirculated with H9N2 and have reassorted their internal genes (figure).4Shi W, Li W, Li X, et al. Phylogenetics of varied subtypes of avian influenza viruses in China: potential threat to humans. Protein Cell (in press).Google Scholar Although the contribution of H9N2 genes to infection in human beings needs to be determined, these genes probably enable H7N9 virus to survive and be transmitted within poultry, because dynamic reassortments of H7N9 with H9N2 genes have been observed,5Cui L Liu D Shi W et al.Dynamic reassortments and genetic heterogeneity of the human-infecting influenza A (H7N9) virus.Nat Commun. 2014; 5: 3142Crossref PubMed Scopus (129) Google Scholar suggesting that H7N9 virus evolved in poultry to become a virus that infects human beings. Hence, reassortment between the prevalent poultry H9N2 viruses (providing genetic segments) and the influenza virus from wild birds could make the influenza evolve to adapt to domestic hosts. Poultry, especially in live markets, would have a pivotal role during the emergence of a novel influenza virus of avian origin. Several subtypes of avian influenza viruses in poultry are capable of infecting human beings, and the next avian influenza virus that could cause mass infections is not known. Therefore, slaughter of poultry carrying H9N2—the incubators for wild-bird-origin influenza viruses—would be an effective strategy to prevent human beings from becoming infected with avian influenza. We call for either a shutdown of live poultry markets or periodic thorough disinfections of these markets in China and any other regions with live poultry markets. We declare that we have no competing interests.