Cross-sectional evaluation of circulating hepatitis B virus RNA and DNA: Different quasispecies?

BACKGROUND Different forms of pregenomic and other hepatitis B virus(HBV)RNA have been detected in patients’sera.These circulating HBV-RNAs may be useful for monitoring covalently closed circular DNA activity,and predicting hepatitis B eantigen seroconversion or viral rebound after nucleos(t)ide analog cessation.Data on serum HBV-RNA quasispecies,however,is scarce.It is therefore important to develop methodologies to thoroughly analyze this quasispecies,ensuring the elimination of any residual HBV-DNA.Studying circulating HBV-RNA quasispecies may facilitate achieving functional cure of HBV infection.AIM To establish a next-generation sequencing(NGS)methodology for analyzing serum HBV-RNA and comparing it with DNA quasispecies.METHODS Thirteen untreated chronic hepatitis B patients,showing different HBV-genotypes and degrees of severity of liver disease were enrolled in the study and a serum sample with HBV-DNA>5 Log10 IU/mL and HBV-RNA>4 Log10 copies/mL was taken from each patient.HBV-RNA was treated with DNAse I to remove any residual DNA,and the region between nucleotides(nt)1255-1611 was amplified using a 3-nested polymerase chain reaction protocol,and analyzed with NGS.Variability/conservation and complexity was compared between HBV-DNA and RNA quasispecies.RESULTS No HBV-DNA contamination was detected in cDNA samples from HBV-RNA quasispecies.HBV quasispecies complexity showed heterogeneous behavior among patients.The Rare Haplotype Load at 1%was greater in DNA than in RNA quasispecies,with no statistically significant differences(P=0.1641).Regarding conservation,information content was equal in RNA and DNA quasispecies in most nt positions[218/357(61.06%)].In 102 of the remaining 139(73.38%),HBV-RNA showed slightly higher variability.Sliding window analysis identified 4 hyper-conserved sequence fragments in each quasispecies,3 of them coincided between the 2 quasispecies:nts 1258-1286,1545-1573 and 1575-1604.The 2 hyper-variable sequence fragments also coincided:nts 1311-1344 and 1461-1485.Sequences between nts 1519-1543 and 1559-1587 were only hyper-conserved in HBV-DNA and RNA,respectively.CONCLUSION Our methodology allowed analyzing HBV-RNA quasispecies complexity and conservation without interference from HBV-DNA.Thanks to this,we have been able to compare both quasispecies in the present study.

Quasispecies structure,cornerstone of hepatitis B virus infection: Mass sequencing approach

Hepatitis B virus(HBV)is a DNA virus with complex replication,and high replication and mutation rates,leading to a heterogeneous viral population.The population is comprised of genomes that are closely related,but not identical;hence,HBV is considered a viral quasispecies.Quasispecies variability may be somewhat limited by the high degree of overlapping between the HBV coding regions,which is especially important in the P and S gene overlapping regions,but is less significant in the X and preCore/Core genes.Despite this restriction,several clinically and pathologically relevant variants have been characterized along the viral genome.Next-generation sequencing(NGS)approaches enable high-throughput analysis of thousands of clonally amplified regions and are powerful tools for characterizing genetic diversity in viral strains.In the present review,we update the information regarding HBV variability and present a summary of the various NGS approaches available for research in this virus.In addition,we provide an analysis of the clinical implications of HBV variants and their study by NGS.

Quasispecies evolution in NS5A region of hepatitis C virus genotype 1b during interferon or combined interferon-ribavirin therapy

AIM: To evaluate the implication of substitutions in the hepatitis C virus (HCV) non-structural 5A (NS5A) protein in the resistance of HCV during mono-interferon (IFN) or combined IFN-ribavirin (IFN-R) therapy. Although NS5A has been reported to interact with the HCV RNA- dependent RNA polymerase, NS5B, as well as with many cellular proteins, the function of NS5A in the life cycle of HCV remains unclear. METHODS: HCV quasispecies were studied by clon- ing and sequencing of sequential isolates from patients infected by HCV genotype 1b. Patients were treated by IFN-α2b for 3 mo followed by IFN-α2b alone or com- bined IFN-R therapy for 9 additional months. Patients were categorized intro two groups based on their re- sponse to the treatments: 7 with sustained virological re- sponse (SVR) (quasispecies = 150) and 3 non-respond- ers (NR) to IFN-R (quasispecies = 106). RESULTS: Prior to treatment, SVR patients displayed a lower complexity of quasispecies than NR patients. Most patients had a decrease in the complexity of quasispe- cies during therapy. Analysis of amino acids substitu- tions showed that the degree of the complexity of the interferon sensitivity-determining region (ISDR) and the V3 domain of NS5A protein was able to discriminate thetwo groups of patients. Moreover, SVR patients displayed more variability in the NS5A region than NR patients. CONCLUSION: These results suggest that detailed mo- lecular analysis of the NS5A region may be important for understanding its function in IFN response during HCV 1b infection.

Characterization of hepatitis B virus X gene quasispecies complexity in mono-infection and hepatitis delta virus superinfection

Hepatitis delta virus(HDV) seems to strongly suppress hepatitis B virus(HBV)replication, although little is known about the mechanism of this interaction. Both these viruses show a dynamic distribution of mutants, resulting in viral quasispecies. Next-generation sequencing is a viable approach for analyzing the composition of these mutant spectra. As the regulatory hepatitis B X protein(HBx) is essential for HBV replication, determination of HBV X gene(HBX)quasispecies complexity in HBV/HDV infection compared to HBV monoinfection may provide information on the interactions between these two viruses.AIM To compare HBV quasispecies complexity in the HBX 5' region between chronic hepatitis delta(CHD) and chronic HBV mono-infected patients.METHODS Twenty-four untreated patients were included: 7/24(29.2%) with HBeAgnegative chronic HBV infection(CI, previously termed inactive carriers), 8/24(33.3%) with HBeAg-negative chronic hepatitis B(CHB) and 9/24(37.5%) with CHD. A serum sample from each patient was first tested for HBV DNA levels.The HBX 5' region [nucleotides(nt) 1255-1611] was then PCR-amplified for subsequent next-generation sequencing(MiSeq, Illumina, United States). HBV quasispecies complexity in the region analyzed was evaluated using incidencebased indices(number of haplotypes and number of mutations), abundancebased indices(Hill numbers of order 1 and 2), and functional indices(mutation frequency and nucleotide diversity). We also evaluated the pattern of nucleotide changes to investigate which of them could be the cause of the quasispecies complexity.RESULTS CHB patients showed higher median HBV-DNA levels [5.4 logIU/mL,interquartile range(IQR) 3.5-7.9] than CHD(3.4 logIU/mL, IQR 3-7.6)(P = n.s.)or CI(3.2 logIU/mL, IQR 2.3-3.5)(P < 0.01) patients. The incidence and abundance indices indicated that HBV quasispecies complexity was significantly greater in CI than CHB. A similar trend was observed in CHD patients, although only Hill numbers of order 2 showed statistically significant differences(CHB2.81, IQR 1.11-4.57 vs CHD 8.87, 6.56-11.18, P = 0.038). There were no significant differences in the functional indices, but CI and CHD patients also showed a trend towards greater complexity than CHB. No differences were found for any HBV quasispecies complexity indices between CHD and CI patients. G-to-A and C-to-T nucleotide changes, characteristic of APOBEC3 G, were higher in CHD and CI than in CHB in genotype A haplotypes, but not in genotype D. The proportion of nt G-to-A vs A-to-G changes and C-to-T vs T-to-C changes in genotype A and D haplotypes in CHD patients showed no significant differences. In CHB and CI the results of these comparisons were dependent on HBV genotype.CONCLUSION The lower-replication CHD and CI groups show a trend to higher quasispecies complexity than the higher-replication CHB group. The mechanisms associated with this greater complexity require elucidation.

Quasispecies dynamics in main core epitopes of hepatitis B virus by ultra-deep-pyrosequencing

AIM:To investigate the variability of the main immunodominant motifs of hepatitis B virus(HBV) core gene by ultra-deep-pyrosequencing(UDPS).METHODS:Four samples(2 genotype A and 2 genotype D) from 4 treatment-na ve patients were assessed for baseline variability.Two additional samples from one patient(patient 4,genotype D) were selected for analysis:one sample corresponded to a 36-mo treatment-free period from baseline and the other to the time of viral breakthrough after 18 mo of lamivudine treatment.The HBV region analyzed covered amino acids 40 to 95 of the core gene,and included the two main epitopic regions,Th50-69 and B74-84.UDPS was carried out in the Genome Sequencer FLX system(454 Life Sciences,Roche).After computer filtering of UDPS data based on a Poisson statistical model,122 813 sequences were analyzed.The most conserved position detected by UDPS was analyzed by site-directed mutagenesis and evaluated in cell culture.RESULTS:Positions with highest variability rates were mainly located in the main core epitopes,confirming their role as immune-stimulating regions.In addition,the distribution of variability showed a relationship with HBV genotype.Patient 1(genotype A) presented the lowest variability rates and patient 2(genotype A) had 3 codons with variability higher than 1%.Patient 3 and 4(both genotype D) presented 5 and 8 codons with variability higher than 1%,respectively.The median baseline frequencies showed that genotype A samples had higher variability in epitopic positions than in the other positions analyzed,approaching significance(P = 0.07,sample 1 and P = 0.05,sample 2).In contrast,there were no significant differences in variability between the epitopic and other positions in genotype D cases.Interestingly,patient 1 presented a completely mutated motif from amino acid 64 to 67(E 64 LMT 67),which is commonly recognized by T helper cells.Additionally,the variability observed in all 4 patients was particularly associated with the E 64 LMT 67 motif.Codons 78 and 79 were highly conserved in all samples,in keeping with their involvement in the interaction between the HBV virion capsid and the surface antigens(HBsAg).Of note,codon 76 was even more conserved than codons 78 and 79,suggesting a possible role in HBsAg interactions or even in hepatitis B e antigen conformation.Sequential analysis of samples from patient 4(genotype D) illustrated the dynamism of the HBV quasispecies,with strong selection of one minor baseline variant coinciding with a decrease in core variability during the treatment-free and lamivudinetreated period.The drop in variability seemed to result from a "steady state" situation of the HBV quasispecies after selection of the variant with greatest fitness.CONCLUSION:Host immune pressure seems to be the main cause of HBV core evolution.UDPS analysis is a useful technique for studying viral quasispecies.

Quasispecies groups in the core promoter region of hepatitis B virus

Objectives: To investigate the mutation of the basic core promoter (BCP) of hepatitis B virus (HBV) and clarify the significance of HBV quasispecies groups in patients with chronic HBV infection. Methods: A set of specific primers was synthesized according to the HBV DNA sequence of a Chinese strain. The BCP was amplified by PCR method from the serum of 40 patients with chronic HBV infection, and the PCR products of 2 patients were subcloned into pGEM Teasy vectors. Polyacrylamide gel elec- trophoresis (PAGE) was employed to display the de- letion mutations, and clones with differential length were selected to be sequenced. Sequence comparison was made to find the difference. Results: Two or three bands were displayed by PAGE in 60% patients. The results of sequence anal- ysis showed that there are some kinds of mutations in the BCP region. The substitution always occurs in TATA-like boxes, especially from T to C on 140 site. The deletion mutations were detected in TA1, TA2 and TA3. The 8bp, 20bp deletion mutations fre- quently happened. Conclusions: There is a hot deletion region in the BCP. The deletion and the substitution in the TATA- like box may influence the expression of preC/C pro- tein. The sequencing results indicate that there are HBV quasispecies groups in patients with chronic HBV infection.

Early Evolution of Hepatitis B Virus Quasispecies During IFN-α Treatment

Objective To investigate the dynamic change of hepatitis B virus quasispecies within complete genome during the early stage of IFN-α treatment and its impact on virological response.Methods Sixteen patients with chronic hepatitis B receiving IFN-α treatment were investigated. HBV DNA was extracted from serum sample at baseline and week 12. The complete genome of HBV was amplified, then cloned and sequenced. The quasispecies heterogeneity of HBV complete genome was depicted at baseline and week 12. Results The quasispecies heterogeneity of the genome except for C-ORF were comparable in three groups at baseline and week 12. The quasispecies diversity at amino acid levels of responders within C-ORF were higher than that of non-responders at baseline. The quasispecies diversity within the C-ORF of partial responders was reduced in the early stage of IFN-α treatment. Furthermore, the mean genetic distance at amino acid levels of partial responders was significantly higher than that of the non-responders at week 12. The evolutionary rate was not different between non-responders and partial responders. Conclusions In the immune clearance phase, the patients who had greater viral quasispecies diversity within C-ORF at amino acid level had more chance to obtain the early virological response during IFN-α treatment.

Influence of quasispecies on virological responses and disease severity in patients with chronic hepatitis C

AIM:To elucidate the influence of quasispecies on virological response and disease severity in patients with chronic hepatitis C. METHODS:Forty seven patients with hepatitis C [32 with chronic active hepatitis (CAH), 9 with cirrhosis, and 6 with hepatocellular carcinoma (HCC)] were screened for the presence of quasispecies by single stranded conformational polymorphism (SSCP) analysis in the hypervariable region (HVR) and non-structural 5B (NS5B) viral genes of hepatitis C virus. The 41 patients excluding those with HCC were on therapy and followed up for a year with the determination of virological response and disease severity. Virus isolated from twenty three randomly selected patients (11 non-responders and 12 showing a sustained virological response) was sequenced for the assessment of mutations. RESULTS:The occurrence of quasispecies was proportionately higher in patients with HCC and cirrhosis than in those with CAH, revealing a significant correlation between the molecular evolution of quasispecies and the severity of disease in patients with hepatitis C. The occurrence of complex quasispecies has a significant association (P < 0.05) with the non-responders, and leads to persistence of infection. Significant differences (P < 0.05) in viral load (log10 IU/mL) were observed among patients infected with complex quasispecies (CQS), those infected with simple quasispecies (SQS) and those with no quasispecies (NQS), after 12 wk (CQS-5.2 ± 2.3, SQS-3.2 ± 1.9, NQS-2.8 ± 2.4) and 24 wk (CQS-3.9 ± 2.2, SQS-3.0 ± 2.2, NQS-2.1 ± 2.3) in the HVR region. However, a statistically significant difference (P < 0.05) was observed between the viral loads of patients infected with CQS and those infected with NQS in NS5B viral gene after 24 wk (CQS-3.9 ± 2.2, SQS-3.0 ± 2.2, and NQS-2.1 ± 2.3) and 48 wk (CQS-3.1 ± 2.7, SQS-2.3 ± 2.4, NQS-2.0 ± 2.3) of therapy. Disease severity was significantly associated with viral load during therapy. The strains isolated from non-responders showed close pairing on phylogeny based on the NS5B gene, but dissimilar HVR regions. This revealed the possibility of the selection of resistant strains during the evolution of quasispecies in NS5B. CONCLUSION:Viral quasispecies may be an important predictor of virological responses to combination therapy in patients with chronic hepatitis C. Complex quasispecies and resistant strains may lead to high viral loads during therapy, with a concerted effect on disease severity.

Rethinking quasispecies theory: From fittest type to cooperative consortia

Recent investigations surprisingly indicate that single RNA "stem-loops" operate solely by chemical laws that act without selective forces, and in contrast, self-ligated consortia of RNA stem-loops operate by biological selection. To understand consortial RNA selection, the concept of single quasi-species and its mutant spectra as drivers of RNA variation and evolution is rethought here. Instead, we evaluate the current RNA world scenario in which consortia of cooperating RNA stem-loops(not individuals) are the basic players. We thus redefine quasispecies as RNA quasispecies consortia(qs-c) and argue that it has essential behavioral motifs that are relevant to the inherent variation, evolution and diversity in biology. We propose that qs-c is an especially innovative force. We apply qs-c thinking to RNA stem-loops and evaluate how it yields altered bulges and loops in the stem-loop regions, not as errors, but as a natural capability to generate diversity. This basic competencenot error-opens a variety of combinatorial possibilities which may alter and create new biological interactions, identities and newly emerged self identity(immunity) functions. Thus RNA stem-loops typically operate as cooperative modules, like members of social groups. Fromsuch qs-c of stem-loop groups we can trace a variety of RNA secondary structures such as ribozymes, viroids, viruses, mobile genetic elements as abundant infection derived agents that provide the stem-loop societies of small and long non-coding RNAs.

Quasispecies of Hepatitis B Virus

Hepatitis B virus(HBV) circulates in blood and replicates in the presence of quasispecies. During HBV replication, HBV DNA polymerase lacks fidelity and proofreading function partly because its exonuclease activity is either absent or deficient. Therefore, HBV genome is mutated with unusually high frequency. And these mutations can affect more than one open reading frame due to overlapping genes. Otherwise, natural substitutions, deletions or insertions involving the Cp/ENⅡ locus in the X gene can significantly alter the extent of viral replication activity. Particular selection pressures such as host immune system and antiviral therapy readily select out escape mutants from this pre-existing quasispecies pool. Antiviral drug resistance in chronic hepatitis B(CHB) can be caused by the viral mutation frequency, the intrinsic mutability of the antiviral target site, the selective pressure exerted by the drug, the magnitude and rate of virus replication, the overall replication fitness of the mutant, the genetic barrier of the compound and the availability of replication space. Potent inhibition of HBV replication could be able to prevent the development of drug resistance because mutagenesis is replication dependent. Viral load may decline to a point where the continued production of quasispecies with the potential to resist new drug treatments no longer occurs, if viral replication can be suppressed for a sufficient length of time.

Different quasispecies with great mutations hide in the same subgroup J field strain of avian leukosis virus

Blood samples were collected from a local strain of chickens associated with serious tumor cases in Shandong Province. The samples were inoculated into chicken embryo fibroblast and DF-1 cells for virus isolation and identification, respectively. The inoculated cells were screened for three common chicken tumor viruses. Nine strains of avian leukosis virus subgroup J （ALV-J） were identified, and were designated LY1201-LYI209. The env gene from the LY1201 strain was amplified and cloned. All nine resultant env clones （clones 01-09） were sequenced, and the gp85 and gp37 amino acid regions were subjected to homology analysis. Clones 01 and 03 had 10 amino acid deletions in the gp85 region compared to the other seven clones, suggesting that at least two quasispecies with obvious mutations coexist in the same field strain. Among these nine clones, three had identical gp85 and gp37 sequences, and were recognized as the dominant LY1201 quasispecies. The amino acid sequence homology of gp37 and gp85 among the nine clones was 98.5%-100.0% and 96.6%-100.0% respectively, suggesting that the gp85 region of the env gene can better display the quasispecies diversity of ALV-J than gp37.

Evolution of quasispecies diversity for porcine reproductive and respiratory syndrome virus under antibody selective pressure

To study the quasispecies diversity of porcine reproductive and respiratory syndrome virus (PRRSV), open reading frame 5 (ORF5) of strain SD0612 was amplified and cloned. Sixty clones of ORF5 were sequenced and analyzed with DNAStar software. Nucleic acid sequence homology was 97.7%-100%, with 78 mutations observed. Among these 60 clones, the sequences of 17 clones were identical and recognized as the dominant quasispecies of strain SD0612. Evolution of SD0612 quasispecies diversity under antibody selective pressure was also studied. SD0612 was passed continuously in the Marc-145 cell line over 40 passages in 6 independent lineages. SD0612 antiserum was not added to lineage A, B, and C cultures; however, antiserum was added to culture medium for lineages D, E, and F. PRRSV ORF5 was then amplified, cloned, and sequenced from each of the 6 lineages, designated as A40-F40. F40 was further passed in Marc-145 cells using 6 independent lineages with or without F40 antiserum for another 40 passages. ORF5 from the 6 newly-derived virus lineages, which we designated as a40-f40, were amplified, cloned and sequenced. The proportion of dominant quasispecies increased with passage number in cell cultures supplemented with antibodies, but decreased when antibodies were lacking. Our work has demonstrated a diversity of quasispecies for ORF5 in PRRSV SD0612. Antibody selective pressure was able to significantly influence quasispecies diversity and promote a dominant quasispecies that was able to evade immune reactions.

Estimate of parameters changing of the Lymantria dispar artificial population in different environmental conditions using the quasispecies model

This paper gives an interpretation of the quasispecies concept for an experiment of growing the Lymantria dispar artificial population.The changes estimate in the population parameters for a significant change in environmental conditions at the stage of hatching caterpillars from the eggs was given.Three numerical and two random parameters were used for quantitative analysis.They characterize the development of individuals of the population at this stage.The parameter changes significance was verified with using statistical tests.The results obtained do not contradict the quasispecies model.The use of fuzzy sets describes the transition from one quasispecies to another at a significant change in environmental conditions.

Mathematical formalization of the process of crossing individuals of different populations within the framework of the quasispecies model

This paper presents a mathematically formalized description of the process of crossing individuals of different populations as a break of the first kind of functional dependencies of the population state vector components.In this case,the validity of the quasispecies model as a model of population development was assumed.The practical interpretation of a mathematically formalized description is considered on the example of an artificial population of Lymantria dispar.The results of the work can be used to assess the development parameters of both natural and artificial populations.

Criticality, adaptability and early-warning signals in time series in a discrete quasispecies model

Complex systems from different fields of knowledge often do not allow a mathematical description or modeling, because of their intricate structure composed of numerous interacting components. As an alternative approach, it is possible to study the way in which observables associated with the system fluctuate in time. These time series may provide valuable information about the underlying dynamics. It has been suggested that complex dynamic systems, ranging from ecosystems to financial markets and the climate, produce generic early-warning signals at the ＂tipping points,＂ where they announce a sudden shift toward a different dynamical regime, such as a population extinction, a systemic market crash, or abrupt shifts in the weather. On the other hand, the framework of Self- Organized Criticality （SOC）, suggests that some complex systems, such as life itself, may spontaneously converge toward a critical point. As a particular example, the quasispecies model suggests that RNA viruses self-organize their mutation rate near the error-catastrophe threshold, where robustness and evolvability are balanced in such a way that survival is optimized. In this paper, we study the time series associated to a classical discrete quasispecies model for different mutation rates, and identify early-warning signals for critical mutation rates near the error-catastrophe threshold, such as irregularities in the kurtosis and a significant increase in the autocorrelation range, reminiscent of 1/f noise. In the present context, we find that the early-warning signals, rather than broadcasting the collapse of the system, are the fingerprint of survival optimization.

Variations and mutations in the hepatitis B virus genome and their associations with clinical characteristics

Hepatitis B virus(HBV) infection is major global issue, because chronic HBV infection is strongly associated with liver cancer. HBV spread worldwide with variousmutations and variations. This variability, called quasispecies, is derived from no proof-reading capacity of viral reverse transcriptase. So far, thousands of studies reported that the variety of genome is closely related to the geographic distribution and clinical characteristics. Recent technological advances including capillary sequencer and next generation sequencer have made in easier to analyze mutations. The variety of HBV genome is related to not only antigenicity of HBs-antigen but also resistance to antiviral therapies. Understanding of these variations is important for the development of diagnostic tools and the appropriate therapy for chronic hepatitis B. In this review, recent publications in relation to HBV mutations and variations are updated and summarized.

Hepatitis C virus genetic variability and evolution

Hepatitis C virus(HCV) has infected over 170 million people worldwide and creates a huge disease burden due to chronic, progressive liver disease. HCV is a singlestranded, positive sense, RNA virus, member of the Flaviviridae family. The high error rate of RNA-dependent RNA polymerase and the pressure exerted by the host immune system, has driven the evolution of HCV into 7 different genotypes and more than 67 subtypes. HCV evolves by means of different mechanisms of genetic variation. On the one hand, its high mutation rates generate the production of a large number of different but closely related viral variants during infection, usually referred to as a quasispecies. The great quasispecies variability of HCV has also therapeutic implications since the continuous generation and selection of resistant or fitter variants within the quasispecies spectrum might allow viruses to escape control by antiviral drugs. On the other hand HCV exploits recombination to ensure its survival. This enormous viral diversity together with some host factors has made it difficult to control viral dispersal. Current treatment options involve pegylated interferon-α and ribavirin as dual therapy or in combination with a direct-acting antiviral drug, depending on the country. Despite all the efforts put into antiviral therapy studies, eradication of the virus or the development of a preventive vaccine has been unsuccessful so far. This review focuses on current available data reported to date on the genetic mechanisms driving the molecular evolution of HCV populations and its relation with the antiviral therapies designed to control HCV infection.

Clinical relevance of hepatitis B virus variants

The hepatitis B virus(HBV) is a global public health problem with more than 240 million people chronically infected worldwide, who are at risk for end-stage liver disease and hepatocellular carcinoma. There are an estimated 600000 deaths annually from complications of HBV-related liver disease. Antiviral therapy with nucleos/tide analogs(NA) targeting the HBV polymerase(P) can inhibit disease progression by long-term suppression of HBV replication. However, treatment may fail with first generation NA therapy due to the emergence of drugresistant mutants, as well as incomplete medication adherence. The HBV replicates via an error-prone reverse transcriptase leading to quasispecies. Due to overlapping open reading frames mutations within the HBV P can cause concomitant changes in the HBV surface gene(S) and vice versa. HBV quasispecies diversity is associated with response to antiviral therapy, disease severity and long-term clinical outcomes. Specific mutants have been associated with antiviral drug resistance, immune escape, liver fibrosis development and tumorgenesis. An understanding of HBV variants and their clinical relevance may be important for monitoring chronic hepatitis B disease progression and treatment response. In this review, we will discuss HBV molecular virology, mechanism of variant development, and their potential clinical impact.

Polymorphisms and resistance mutations of hepatitis C virus on sequences in the European hepatitis C virus database

AIM To evaluate the occurrence of resistant mutations in treatment-na?ve hepatitis C virus(HCV) sequences deposited in the European hepatitis C virus database(euH CVdb). METHODS The sequences were downloaded from the eu HCVdb(https://euhcvdb.ibcp.fr/eu HCVdb/). The search was performed for full-length NS3 protease, NS5 A and NS5 B polymerase sequences of HCV, separated by genotypes 1a, 1b, 2a, 2b and 3a, and resulted in 798 NS3, 708 NS5 A and 535 NS5 B sequences from HCV genotypes1a, 1b, 2a, 2b and 3a, after the exclusion of sequences containing errors and/or gaps or incomplete sequences, and sequences from patients previously treated with direct antiviral agents(DAA). The sequence alignment was performed with MEGA 6.06 MAC and the resulting protein sequences were then analyzed using the BioE dit 7.2.5. for mutations associated with resistance. Only positions that have been described as being associated with failure in treatment in in vivo studies, and/or as conferring a more than 2-fold change in replication in comparison to the wildtype reference strain in in vitro phenotypic assays were included in the analysis.RESULTS The Q80 K variant in the NS3 gene was the most prevalent mutation, being found in 44.66% of subtype 1a and 0.25% of subtype 1b. Other frequent mutations observed in more than 2% of the NS3 sequences were: I170V(3.21%) in genotype 1a, and Y56F(15.93%), V132I(23.28%) and I170V(65.20%) in genotype 1b. For the NS5 A, 2.21% of the genotype 1a sequences have the P58 S mutation, 5.95% of genotype 1b sequences have the R30 Q mutation, 15.79% of subtypes 2a sequences have the Q30 R mutation, 23.08% of subtype 2b sequences have a L31 M mutation, and in subtype 3a sequences, 23.08% have the M31 L resistant variants. For the NS5 B, the V321 L RAV was identified in 0.60% of genotype 1a and in 0.32% of genotype 1b sequences, and the N142 T variant was observed in 0.32% of subtype 1b sequences. The C316 Y, S556 G, D559 N RAV were identified in 0.33%, 7.82% and 0.32% of genotype 1b sequences, respectively, and were not observed in other genotypes.CONCLUSION HCV mutants resistant to DAAs are found in low frequency, nevertheless they could be selected and therapy could fail due resistance substitutions in HCV genome.

The Role of Viral Mutation in the Pathogenesis of Chronic Viral Hepatitis

The quasispecies nature of hepatitis B and C virus (HBV, HCV) plays an important role in the pathogenesis, immune escape and drug resistance during chronic infection. Although there is still a lack of effective treatment for hepatitis C, a series of nucleoside analogs (NA) have been developed for the treatment of hepatitis B. NA resistant HBV mutants can accumulate during prolonged therapy and lead to the failure of anti-HBV therapy. Switching to other sensitive NAs can inhibit the emerged resistant mutants. Therefore, understanding the evolution of viral quasispecies under drug pressure is crucial for the establishment of antiviral strategy and the monitoring of antiviral process. Immune response and escape are complicated process, during which both host and virus factors may play their roles. Further understanding of the interaction and interrelationship between host and these viruses may lead to optimized prevention, diagnosis and treatment for chronic hepatitis.