Effect of reassortment on the nucleotide and amino acid changes of human A/H3N2 RNP subunits during 1998–2009

In vitro reassortment between Infectious Pancreatic Necrosis Virus (IPNV) strains: The mechanisms involved and its effect on virulence

Reassortment is one of the main mechanisms of evolution in dsRNA viruses with segmented genomes. It contributes to generate genetic diversity and plays an important role in the emergence and spread of new strains with altered virulence. Natural reassorment has been demonstrated among infectious pancreatic necrosis-like viruses (genus Aquabirnavirus, Birnaviridae). In the present study, coinfections between different viral strains, and genome sequencing by the Sanger and Illumina methods were applied to analyze the frequency of reassortment of this virus in vitro, the possible mechanisms involved, and its effect on virulence. Results have demonstrated that reassortment is a cell-dependent and non-random process, probably through differential expression of the different mRNA classes in the ribosomes of a specific cell, and by specific associations between the components to construct the ribonucleoprotein (RNP) complexes and/or RNP cross-inhibition. However, the precise mechanisms involved, known in other viruses, still remain to be demonstrated in birnaviruses.

Comparison of influenza virus replication fidelity in vitro using selection pressure with monoclonal antibodies

The replication fidelity of reassortant A/Fujian/411/02(H3N2)-like influenza viruses was assessed by in vitro detection of escape mutants developing under selective pressure from monoclonal antibodies. The results showed A/Wyoming/3/03(H3N2) possessed lower fidelity relative to the A/California/7/04(H3N2) and A/Wisconsin/57/05(H3N2) viruses through the emergence of mutant viruses carrying H156Q hemagglutinin mutation which allows antibody escape. Using the neutralization assay to compare the fidelity of reassortant pandemic A/California/7/09(H1N1) viruses, the pandemic virus was shown to possess relative higher fidelity compared to A/Wyoming/3/03. This higher fidelity may contribute to the lack of major antigenic changes in the pandemic virus since the emergence in 2009.

Exploring the molecular epidemiology and evolutionary dynamics of influenza A virus in Taiwan

The evolution and population dynamics of human influenza in Taiwan is a microcosm of the viruses circulating worldwide, which has not yet been studied in detail. We collected 343 representative full genome sequences of human influenza A viruses isolated in Taiwan between 1979 and 2009. Phylogenetic and antigenic data analysis revealed that H1N1 and H3N2 viruses consistently co-circulated in Taiwan, although they were characterized by different temporal dynamics and degrees of genetic diversity. Moreover, influenza A viruses of both subtypes underwent internal gene reassortment involving all eight segments of the viral genome, some of which also occurred during non-epidemic periods. The patterns of gene reassortment were different in the two subtypes. The internal genes of H1N1 viruses moved as a unit, separately from the co-evolving HA and NA genes. On the other hand, the HA and NA genes of H3N2 viruses tended to segregate consistently with different sets of internal gene segments. In particular, as reassortment occurred, H3HA always segregated as a group with the PB1, PA and M genes, while N2NA consistently segregated with PB2 and NP. Finally, the analysis showed that new phylogenetic lineages and antigenic variants emerging in summer were likely to be the progenitors of the epidemic strains in the following season. The synchronized seasonal patterns and high genetic diversity of influenza A viruses observed in Taiwan make possible to capture the evolutionary dynamic and epidemiological rules governing antigenic drift and reassortment and may serve as a "warning" system that recapitulates the global epidemic.