Increased hepatitis B virus quasispecies diversity is correlated with liver fibrosis progression.

Host immune response and viral factors are involved in disease progression in patients with chronic hepatitis B virus (HBV) infection. However, the relationship between HBV quasispecies and liver fibrosis progression remains unclear. In this study, 447 patients with chronic HBV infection, including 239 with chronic hepatitis B (CHB), 104 with liver cirrhosis (LC) and 104 with hepatocellular carcinoma (HCC) were enrolled. The 239 CHB patients were divided into groups F1, F2, and F3 according to liver fibrosis score. Four fragments of the HBV genome were determined and analyzed using next-generation sequencing. Specific mutations, such as A1762T, G1764A and G1896A, in the BCP/PC region were more common in patients with advanced liver disease and formed the majority of the viral quasispecies pool in patients with LC and HCC. The viral complexity and diversity increased as the fibrosis progressed, especially in patients with CHB who were comparable in age but at different stages of fibrosis. Patients with early-stage fibrosis experienced higher purifying selection pressure in the four sequenced regions, whereas different protein-coding region experienced different negative selection with disease progression. HBV quasispecies diversity may increase fibrosis progression in CHB patients with aging under immune selection.

Characterization of betanodavirus quasispecies influences on the subcellular localization and expression of tumor necrosis factor (TNF).

The aim of this study was to investigate the influence of variant coat proteins (CPs) from different quasispecies of betanodavirus on diverse aspects of nodavirus-induced pathogenesis. It is known that variant CPs can acquire either nuclear or cytoplasmic localization, depending on the nodavirus CP genotype, and this variation may arise during viral replication and influence the regulation of host and viral gene transcription. To investigate the role of these variant CPs in pathogenesis, six variant CP expression plasmids were constructed, each containing different quasispecies CP variants from nodavirus genotype red spotted grouper nervous necrosis virus (RGNNV). The CP expression plasmids were transiently transfected into grouper GF-1 cells. At different times, the cell cycle and cell proliferation were assayed using flow cytometry and methyl thiazolyl tetrazolium (MTT) assays, respectively. The proportion of G2/M-phase GF-1 cells transfected with CP expression plasmids was higher than that of cells transfected with the blank plasmid, especially in regards to quasispecies 2 (QS2). The proliferation ratio of cells transfected with the CP expression plasmids was significantly higher than that of cells transfected with the blank plasmid, with the exception of QS6. We also found that the different quasispecies CPs downregulated the promoter activity of the tumor necrosis factor (TNF) gene to different degrees. In addition, this is the first report showing the betanodavirus CP derived from different quasispecies of RGNNV provide evidence of a chronically nodavirus-infected grouper. Overall, this study represents the first comprehensive analysis of variant CPs from grouper with persistent nodavirus infections and their effects on different aspects of pathogenesis.

Why, so far, have epidemics always eventually petered out? Quasispecies theory suggests a (testable!) answer.

In this paper, it is argued that the fact that, so far, even the worst and most far-reaching epidemics-from the Plague of Athens in 430 BC and the Plague of Justinian in 541/542 AD to the Hong Kong Flu from 1968/69-always finally petered out can be explained using Manfred Eigen's quasispecies concept: Indeed, as the infectious agents, while duplicating themselves in the infected organisms, mutate all the time, these infected organisms carry along quite a multitude of mutational variants or-in Manfred Eigen's terms-a whole quasispecies of infectious agents implying that, within that quasispecies, those variants that differ from the wild type may actually serve as some kind of vaccination program when infecting some previously uninfected persons. In this context, some data regarding various recent epidemics will also be illustrated, using Daniel Huson's SplitsTree software tool.

Quasispecies and virus.

Quasispecies theory has been instrumental in the understanding of RNA virus population dynamics because it considered for the first time mutation as an integral part of the replication process. The key influences of quasispecies theory on experimental virology have been: (1) to disclose the mutant spectrum nature of viral populations and to evaluate its consequences; (2) to unveil collective properties of genome ensembles that can render a mutant spectrum a unit of selection; and (3) to identify new vulnerability points of pathogenic RNA viruses on three fronts: the need to apply multiple selective constraints (in the form of drug combinations) to minimize selection of treatment-escape variants, to translate the error threshold concept into antiviral designs, and to construct attenuated vaccine viruses through alterations of viral polymerase copying fidelity or through displacements of viral genomes towards unfavorable regions of sequence space. These three major influences on the understanding of viral pathogens preceded extensions of quasispecies to non-viral systems such as bacterial and tumor cell collectivities and prions. These developments are summarized here.