In a study published Wednesday in Nature Communications, researchers discovered that certain strains of H7N9 have mutated to become “highly resistant” to antivirals like Tamiflu while maintaining high levels of pathogenicity. This is not normal. Normally when a virus acquires drug-resistance through mutation, this mutation attenuates it, decreasing viral virulence or replication ability. The study authors write, “in stark contrast to oseltamivir-resistant seasonal influenza A(H3N2) viruses, H7N9 virus replication and pathogenicity in these models are not substantially altered by the acquisition of high-level oseltamivir resistance”. Moreover, drug resistance in highly pathogenic avian influenza (HPAI) viruses is usually limited to amantadine resistance; infact, many influenza A and B strains are already resistant to amantadine. This means that in many cases, the only effective antivirals are neuraminidase (NA) inhibitors. Luckily, resistance to NA inhibitors is rare. Unluckily, some strains of H7N9 appear to have it.
Read the full paper here.
(image of H7N9: CDC/Cynthia S. Goldsmith and Thomas Rowe; false color added by author)