Characterization of Oseltamivir-Resistant 2009 H1N1 Pandemic Influenza A Viruses

Abstract

Influenza viruses resistant to antiviral drugs emerge frequently. Not surprisingly, the widespread treatment in many countries of patients infected with 2009 pandemic influenza A (H1N1) viruses with the neuraminidase (NA) inhibitors oseltamivir and zanamivir has led to the emergence of pandemic strains resistant to these drugs. Sporadic cases of pandemic influenza have been associated with mutant viruses possessing a histidine-to-tyrosine substitution at position 274 (H274Y) in the NA, a mutation known to be responsible for oseltamivir resistance. Here, we characterized in vitro and in vivo properties of two pairs of oseltaimivir-sensitive and -resistant (possessing the NA H274Y substitution) 2009 H1N1 pandemic viruses isolated in different parts of the world. An in vitro NA inhibition assay confirmed that the NA H274Y substitution confers oseltamivir resistance to 2009 H1N1 pandemic viruses. In mouse lungs, we found no significant difference in replication between oseltamivir-sensitive and -resistant viruses. In the lungs of mice treated with oseltamivir or even zanamivir, 2009 H1N1 pandemic viruses with the NA H274Y substitution replicated efficiently. Pathological analysis revealed that the pathogenicities of the oseltamivir-resistant viruses were comparable to those of their oseltamivir-sensitive counterparts in ferrets. Further, the oseltamivir-resistant viruses transmitted between ferrets as efficiently as their oseltamivir-sensitive counterparts. Collectively, these data indicate that oseltamivir-resistant 2009 H1N1 pandemic viruses with the NA H274Y substitution were comparable to their oseltamivir-sensitive counterparts in their pathogenicity and transmissibility in animal models. Our findings highlight the possibility that NA H274Y-possessing oseltamivir-resistant 2009 H1N1 pandemic viruses could supersede oseltamivir-sensitive viruses, as occurred with seasonal H1N1 viruses.

The H275Y Neuraminidase Mutation of the Pandemic A/H1N1 Influenza Virus Lengthens the Eclipse Phase and Reduces Viral Output of Infected Cells, Potentially Compromising Fitness in Ferrets

“…Unlike the growth of pre-2007 seasonal H1N1 strains, that of the H1N1pdm09 H275Y MUT (H1N1pdm09-MUT) strain is not severely compromised in vitro or in ferrets (9,12,15,31). Contact transmissions of H1N1pdm09-MUT between ferrets have been successful in all of the experiments reported (15,16,35,38,45).…”

“…Contact transmissions of H1N1pdm09-MUT between ferrets have been successful in all of the experiments reported (15,16,35,38,45). The results concerning airborne transmission, however, have been mixed, with some studies finding comparable (45,46) or nonsignificant differences (12) in efficiency and others finding that H1N1pdm09-MUT was transmitted less efficiently (16) (P ϭ 0.04, two-tailed Mantel-Cox test; M. É. Hamelin, personal communication) or suffered a delay with respect to the susceptible strain (31). Concise reviews of this prior work can be found elsewhere (7,26,42).…”

Molecular characterization of influenza A(H1N1)pdm09 virus circulating during the 2009 outbreak in Thua Thien Hue, Vietnam

“…Our analyses were conducted on only four randomized isolates, which were collected in the same place in a short period of time and after a few months from the beginning of the pandemic, limiting the possibility of greater genetic variability. Worldwide, recent reports have shown that a small proportion of influenza A(H1N1)pdm09 viruses have an NA mutant substitution at H275Y (N1 numbering, H275Y) that has been reported to give a high degree of resistance to oseltamivir [17,18,19,20]. This mutant isolate of influenza A(H1N1)pdm09 virus was also detected in Vietnam [18,20,21].…”

“…Worldwide, recent reports have shown that a small proportion of influenza A(H1N1)pdm09 viruses have an NA mutant substitution at H275Y (N1 numbering, H275Y) that has been reported to give a high degree of resistance to oseltamivir [17,18,19,20]. This mutant isolate of influenza A(H1N1)pdm09 virus was also detected in Vietnam [18,20,21]. Thua Thien Hue isolates had several mutated substitutions in the NA amino acid sequences; however, they were not harboring the mutant substitution at H275Y.…”

Clinical and virologic outcomes in patients with oseltamivir‐resistant seasonal influenza A (H1N1) infections: results from a clinical trial

“…In one study, oseltamivir treatment did not decrease viral titers in ferrets infected with influenza A (H5N1) viruses containing the H275Y mutation 15 and in another, oseltamivir did not affect viral replication in mice infected with 2009 pandemic influenza A (H1N1) viruses with the H275Y mutation 16 . No study reports measured the effect of oseltamivir on illness severity and viral shedding in animals infected with seasonal A (H1N1) viruses with H275Y.…”