Adamantane-Resistant Influenza A Viruses in the World (1902–2013): Frequency and Distribution of M2 Gene Mutations

TLDR

Adamantanes have long been used to prevent and treat influenza A infections, yet resistance to these drugs is widespread worldwide. The study aims to investigate the frequency and distribution of M2 gene mutations conferring adamantane resistance in influenza A viruses from 1902 to 2013. The authors analyzed 31,251 M2 protein sequences from HA subtypes H1–H17 and compared the prevalence of resistance‑associated mutations (L26F, V27A, A30T, A30V, S31N, G34E, L38F). The analysis revealed that 45.2 % of influenza A viruses were adamantane‑resistant, mainly due to the S31N mutation (95 %), with other mutations rare, and that resistance varied by HA subtype, host species, year, and region, highlighting the need for ongoing surveillance.

Abstract

Adamantanes (amantadine and rimantadine) have been used to prevent and treat influenza A virus infections for many years; however, resistance to these drugs has been widely reported in the world. To investigate the frequency and distribution of M2 gene mutations in adamantane-resistant influenza variants circulated in the world between 1902 and 2013, 31251 available M2 protein sequences from different HA-subtype influenza A viruses (H1–H17) were analyzed and adamantane resistance-associated mutations were compared (L26F, V27A, A30T, A30V, S31N, G34E, and L38F). We find that 45.2% (n = 14132) of influenza A (H1–H17) viruses circulating globally were resistant to adamantanes, and the vast majority of resistant viruses (95%) bear S31N mutations. Whereas, only about 1% have V27A mutations and other mutations (L26F, A30T, G34E, and L38F) were extremely rare (their prevalence appeared to be < 0.2%). Our results confirm that H1, H3, H5, H7, H9, and H17 subtype influenza A viruses exhibit high-level resistance to adamantanes. In contrast, the appearance of adamantane-resistant mutants in H2, H4, H6, H10, and H11 subtypes was rare. However, no adamantane resistance viruses were identified among other HA subtypes (H8, H12–H16). Our findings indicate that the frequency and distribution of adamantane-resistant influenza variants varied among different HA subtypes, host species, years of isolation, and geographical areas. This comprehensive study raises concerns about the increasing prevalence of adamantane-resistant influenza A viruses and highlights the importance of monitoring the emergence and worldwide spread of adamantane-resistant variants.