Viral Evolution

ReseaRch highlights

Viral eVolution Pandemic flu can go from bad to worse Despite the rapid worldwide spread genotyped 25 clones from each of in the G1 and G2 strains, the authors of the current pandemic influenza the three groups and sequenced the assayed the viral polymerase activi- more virulent virus, no variants of increased genomes of six of these clones for ties and receptor specificities and pandemic pathogenicity have so far been identi- each group. In all co-infections, the found that, when compared with the fied from patients, which suggests pandemic genotype predominated parental strains, G1 exhibited higher influenza a stable viral phenotype. However, in the viral offspring. However, when polymerase activity at 37 °C, whereas strains can it is not clear whether this situation the seasonal strain dominated in the G2 showed higher polymerase activ- indeed emerge may change in the near future. Now, initial co-infection mixture, most ity at 33 °C, the temperature of the owing to Richard Webby and colleagues show of the progeny carried the seasonal mammalian airway. Furthermore, G1 that the emergence of more virulent haemagglutinin (HA) gene in a displayed a unique pattern of binding mutations and strains of pandemic influenza can pandemic background, as well as to α2,6-sialyl receptors. re-assortment indeed occur by re-assortment with a mutation (D87N) in polymerase This study demonstrates that with seasonal a seasonal influenza virus and by basic protein 2 (PB2). In the other more virulent pandemic influenza viruses. spontaneous mutations. two groups, the viral offspring often strains can indeed emerge owing to The influenza virus genome harboured two mutations, K154Q in mutations and re-assortment with consists of eight separate segments HA and L295P in polymerase acidic seasonal viruses — some of which of RNA. Therefore, when a cell is protein (PA). have become resistant to common infected by two different viral geno- Two representative strains of the antiviral drugs. The authors suggest types, offspring can combine seg- new variants were selected for further that these adaptive changes identified ments from the two infecting viruses, analysis: G1 (carrying mutations in the G1 and G2 variants could be producing new genetic combinations. in HA and PA) and G2 (with the used as potential markers of increased To explore possible scenarios of seasonal-strain HA and the mutation pathogenicity during the surveillance influenza virus evolution, Webby et al. in PB2). Interestingly, G1 and G2 dis- of pandemic influenza viruses. co-infected normal cells from human played higher replication levels than Cesar Sanchez bronchial epithelium with three the parental pandemic and seasonal different ratios of a seasonal strain strains, both in cell culture and in oriGinal reSearCH PaPer Ilyushina, N. A. (A/New Jersey/15/07) and a pandemic ferrets (a common animal model for et al. Does pandemic A/H1N1 virus have the potential to become more pathogenic? mBio 1, strain (A/Tennessee/1-560/09). influenza studies). To explore pos- e00249‑10 (2010). After ten successive passages, they sible roles of the observed mutations