Reintroduction of highly pathogenic avian influenza A H7N9 virus in southwestern China

Highly pathogenic (HP) avian influenza A H7N9 virus has emerged in China since 2016. In recent years, it has been most prevalent in northern China. However, several strains of HP H7N9 reappeared in southwestern China (Yunnan Province) in 2021. As a result, we are wondering if these viruses have re-emerged in situ or been reintroduced. Here, we present phylogenetic evidence that the HP H7N9 viruses isolated in Yunnan emigrated from northern to southwestern China in 2020. The northern subregion of China has become a novel epicenter in HP H7N9 dissemination. Meanwhile, a cleavage motif re-emerged due to the T341I mutation, implying a parallel evolution. This cross-region transmission, which originated in non-adjacent provinces and traveled a great geographic distance in an unknown way, indicates that HP H7N9 dissemination did not halt in 2020, even under the shadow of the COVID-19 pandemic. Additional surveillance studies in poultry are required to determine the HP H7N9 virus's geographic distribution and spread.

Automated summary

Highly pathogenic H7N9 avian influenza virus has emerged in China since 2016, with recent prevalence in northern China. However, in 2021, several strains of highly pathogenic H7N9 reappeared in southwestern China, raising questions about their re-emergence or reintroduction. Phylogenetic evidence shows that the H7N9 viruses isolated in Yunnan in 2020 migrated from northern to southwestern China, indicating a novel epicenter in H7N9 dissemination. Furthermore, a cleavage motif re-emerged due to the T341I mutation, suggesting parallel evolution. This cross-region transmission, despite the COVID-19 pandemic, highlights the need for additional surveillance studies to determine the geographic distribution and spread of the highly pathogenic H7N9 virus.