Natural Reassortment of Eurasian Avian-Like Swine H1N1 and Avian H9N2 Influenza Viruses in Pigs

Published in Emerging Infectious Diseases, a study led by Prof. Leo Poon and Prof. Malik Peiris from HKU-Pasteur Research Pole and the Centre for Immunology & Infection over swine influenza A viruses (IAVs) suggested that H9N2 viruses are infecting pigs and reassorting with swine influenza viruses in China.

Through a monthly influenza surveillance program of imported pigs, individual nasal swabs were regularly collected and then subjected to IAV isolation by using MDCK cells. In total, 8 IAVs were isolated between August and September 2021. The team responsible for this research isolated a swine H1N1 IAV which contains PB2, polymerase acidic, and NA gene segments derived from the pH1N1 lineage. The A/swine/HK/NS419/2021 isolate featured a PB1 gene segment of SH/F/98‐like lineage and an M gene segment of G1-like H9N2 lineage.

Similar PB1 and M sequences have been detected in zoonotic viruses in humans (see related Figure), PB1 in H10N8 and M in H7N9, but Profs. Poon and Peiris did not find mutations known for mammalian host adaptation in these 2 segments. The isolated encoded proteins of the PB1 and M gene segments featured amino acid sequences rarely observed in mammalian and avian IAVs, including H9 (PB1, 97K, 156N, 397V, 535V, 688I, and 704T; M1, 31I and 46V; and M2, 25S), however it could not bedetermined whether these were random or adaptive mutations. It appears that many zoonotic IAVs in humans have genes derived from H9N2 subtypes. Profs. Poon and Peiris’s results suggest that avian H9N2 IAVs are infecting swine and reassorting with swine IAVs, which indicates the need for continued monitoring of swine IAVs in both China and outlying regions.


>>> Natural Reassortment of Eurasian Avian-Like Swine H1N1 and Avian H9N2 Influenza Viruses in Pigs

Figure. Phylogenetic tree of polymerase basic 1 (A) and matrix (B) gene sequences of swine influenza viruses from China and reference sequences. Bold indicates human H7N9 and H10N8 sequences. (more)