Phenotypic and Genetic Characterization of Avian Influenza H5N2 Viruses with Intra- and Inter-Duck Variations in Taiwan

Pathogenic assessment of avian influenza viruses in migratory birds

Several subtypes of avian influenza (AI) viruses have caused human infections in recent years; however, there is a severe knowledge gap regarding the capacity of wild bird viruses to infect mammals. To assess the risk of mammalian infection by AI viruses from their natural reservoirs, a panel of isolates from 34 wild birds was examined in animal models. All selected AI virus subtypes were found to predominantly possess Eurasian lineage, although reassortment with North American lineage AI viruses was also noted in some isolates. When used to infect chickens, 20 AI isolates could be recovered from oropharyngeal swabs at 5 days post-infection (dpi) without causing significant morbidity. Similarly, mild to no observable disease was observed in mice infected with these viruses although the majority replicated efficiently in murine lungs. As expected, wild bird AI isolates were found to recognize avian-like receptors, while a few strains also exhibited detectable human-like receptor binding. Selected strains were further tested in ferrets, and 15 out of 20 were found to shed the virus in the upper respiratory tract until 5 dpi. Overall, we demonstrate that a diversity of low-pathogenic AI viruses carried by wild migratory birds have the capacity to infect land-based poultry and mammalian hosts while causing minimal signs of clinical disease. This study reiterates that there is a significant capacity for interspecies transmission of AI viruses harboured by wild aquatic birds. Thus, these viruses pose a significant threat to human health underscoring the need for continued surveillance.

Optimization of N-Substituted Oseltamivir Derivatives as Potent Inhibitors of Group-1 and -2 Influenza A Neuraminidases, Including a Drug-Resistant Variant

On the basis of our earlier discovery of N1-selective inhibitors, the 150-cavity of influenza virus neuraminidases (NAs) could be further exploited to yield more potent oseltamivir derivatives. Among the synthesized compounds, 15b and 15c were exceptionally active against both group-1 and -2 NAs. Especially for 09N1, N2, N6, and N9 subtypes, they showed 6.80-12.47 and 1.20-3.94 times greater activity than oseltamivir carboxylate (OSC). They also showed greater inhibitory activity than OSC toward H274Y and E119V variant. In cellular assays, they exhibited greater potency than OSC toward H5N1, H5N2, H5N6, and H5N8 viruses. 15b demonstrated high metabolic stability, low cytotoxicity in vitro, and low acute toxicity in mice. Computational modeling and molecular dynamics studies provided insights into the role of R group of 15b in improving potency toward group-1 and -2 NAs. We believe the successful exploitation of the 150-cavity of NAs represents an important breakthrough in the development of more potent anti-influenza agents.