Recombination between sequences of hepatitis B virus from different genotypes

Detection technology and clinical applications of serum viral products of hepatitis B virus infection

Viral hepatitis, caused by its etiology, hepatitis virus, is a public health problem globally. Among all infections caused by hepatitis-associated viruses, hepatitis B virus (HBV) infection remains the most serious medical concern. HBV infection particularly affects people in East Asia and Africa, the Mediterranean region, and Eastern Europe, with a prevalence rate of > 2%. Currently, approximately 1 billion people worldwide are infected with HBV, and nearly 30% of them experience chronic infection. Chronic HBV infection can lead to chronic hepatitis B (CHB), liver cirrhosis, and hepatocellular carcinoma (HCC), resulting in the related death of approximately 1 million people annually. Although preventative vaccines and antiviral therapies are currently available, there is no cure for this infection. Clinical testing is not only the gateway for diagnosis of HBV infection, but also crucial for judging the timing of medication, evaluating the effect of antiviral therapy, and predicting the risk of relapse after drug withdrawal in the whole follow-up management of hepatitis B infected persons. With advances in detection technology, it is now possible to measure various viral components in the blood to assess the clinical status of HBV infection. Serum viral products of HBV infection, such as HBV DNA, HBV RNA, hepatitis B surface antigen, hepatitis B e-antigen, and hepatitis B core-related antigen, are non-invasive indicators that are critical for the rapid diagnosis and management of related diseases. Improving the sensitivity of monitoring of these products is essential, and the development of corresponding detection technologies is pivotal in achieving this goal. This review aims to offer valuable insights into CHB infection and references for its effective treatment. We provide a comprehensive and systematic overview of classical and novel methods for detecting HBV serum viral products and discusses their clinical applications, along with the latest research progress in this field.

Phylogenetic and drug- and vaccine-resistance profiles of Hepatitis B Virus among children with HIV co-infection in Pakistan

INTRODUCTION

HIV-1 and hepatitis B virus (HBV) share common routes of transmission and therefore co-infection is common. In 2019, an HIV-1 outbreak that resulted in >1000 children being infected, predominantly through nosocomial transmission, occurred in Sindh, Pakistan. We conducted a phylogenetic and drug resistance analysis of the HBV Reverse Transcriptase (RT) gene in children with HIV-1 and HBV co-infection.

METHODOLOGY

Blood samples were collected from 321 children with HIV who were recruited as part of a study to investigate the HIV-1 outbreak. All samples were tested for HBV surface antigen (HBsAg) using an ELISA assay, and positive samples were used to amplify and sequence the HBV RT gene. The phylogenetic relationship between sequences was analyzed, and drug- and vaccine- resistance mutations in the RT gene were explored.

RESULTS

Of 321 samples, 23% (n = 75) were positive for HBsAg on ELISA. Phylogenetic analysis of the sequences revealed that 63.5% of HBV sequences were sub-genotype D1, while the rest were sub-genotype D2. Cluster analysis revealed grouping of sub-genotype D1 sequences exclusively with Pakistani sequences, while clustering of sub-genotypes D2 predominantly with global sequences. The 236Y mutation associated with resistance to tenofovir was observed in 2.8% of HBV sequences. Additionally, seven vaccine escape mutations were observed, the most common being 128 V.

CONCLUSION

Our study suggests ongoing transmission of HBV D1 and D2 sub-genotypes in the HIV-1 co-infected population, likely nosocomially, given common routes of HVB and HIV-1 transmission. The prevalence of major HBV drug- and vaccine-resistant mutations remains low. Surveillance for further transmissions and the possible emergence of major drug- or vaccine-resistant variants is required.

Complex structural variations in non-human primate hepatitis B virus

BACKGROUND

Recent genome sequence technology has revealed a novel type of genetic rearrangement referred to as complex structural variations (SVs). Previous studies have elucidated the complex SVs in human hepatitis B viruses (HBVs). In this study, we investigated the existence of complex SVs in HBVs from non-human primates (NHPs).

METHODS

Searches for nucleotide sequences of NHP HBV were conducted using the PubMed, and genetic sequences were retrieved from databases. The candidate genetic sequences harboring complex SVs were analyzed using the CLUSTALW program and MAFFT. Additional bioinformatical analyses were performed to determine strains with complex SVs and to elucidate characteristics of NHP HBV strains.

RESULTS

One hundred and fifty-four HBV strains from NHPs were identified from databases. SVs and complex SVs were observed in 11 (7.1%) strains. Three gibbon HBV (GiHBV) strains showed complex SVs consisting of an insertion and a deletion in the pre-S1 region. One GiHBV strain possessed a 6-nt insertion, which are normally specific to human HBV genotype A (HBV/A) in the Core region, and further analyses clarified that the 6-nt insertion was not caused by recombination, but rather by simple insertion. Another chimpanzee HBV strain showed complex SVs in the pre-S1 region, which were composed of human HBV/E, G-specific polymorphic SV, and an additional 6-nt insertion.

CONCLUSIONS

In this study, complex SVs were observed in HBV strains from NHPs, in addition to human HBV strains, as shown in previous studies. These data suggest that complex SVs could also be found in other members of hepadnaviruses, and may play a role in their genetic diversity.

Novel Genetic Rearrangements in Hepatitis B Virus: Complex Structural Variations and Structural Variation Polymorphisms

Chronic hepatitis B virus (HBV) causes serious clinical problems, such as liver cirrhosis and hepatocellular carcinoma. Current antiviral treatments suppress HBV; however, the clinical cure rate remains low. Basic research on HBV is indispensable to eradicate and cure HBV. Genetic alterations are defined by nucleotide substitutions and canonical forms of structural variations (SVs), such as insertion, deletion and duplication. Additionally, genetic changes inconsistent with the canonical forms have been reported, and these have been termed complex SVs. Detailed analyses of HBV using bioinformatical applications have detected complex SVs in HBV genomes. Sequence gaps and low sequence similarity have been observed in the region containing complex SVs. Additionally, insertional motif sequences have been observed in HBV strains with complex SVs. Following the analyses of complex SVs in the HBV genome, the role of SVs in the genetic diversity of orthohepadnavirus has been investigated. SV polymorphisms have been detected in comparisons of several species of orthohepadnaviruses. As mentioned, complex SVs are composed of multiple SVs. On the contrary, SV polymorphisms are observed as insertions of different SVs. Up to a certain point, nucleotide substitutions cause genetic differences. However, at some point, the nucleotide sequences are split into several particular patterns. These SVs have been observed as polymorphic changes. Different species of orthohepadnaviruses possess SVs which are unique and specific to a certain host of the virus. Studies have shown that SVs play an important role in the HBV genome. Further studies are required to elucidate their virologic and clinical roles.

HBV evolution and genetic variability: Impact on prevention, treatment and development of antivirals

Hepatitis B virus (HBV) poses a major global health burden with 260 million people being chronically infected and 890,000 dying annually from complications in the course of the infection. HBV is a small enveloped virus with a reverse-transcribed DNA genome that infects hepatocytes and can cause acute and chronic infections of the liver. HBV is endemic in humans and apes representing the prototype member of the viral family Hepadnaviridae and can be divided into 10 genotypes. Hepadnaviruses have been found in all vertebrate classes and constitute an ancient viral family that descended from non-enveloped progenitors more than 360 million years ago. The de novo emergence of the envelope protein gene was accompanied with the liver-tropism and resulted in a tight virus-host association. The oldest HBV genomes so far have been isolated from human remains of the Bronze Age and the Neolithic (~7000 years before present). Despite the remarkable stability of the hepadnaviral genome over geological eras, HBV is able to rapidly evolve within an infected individual under pressure of the immune response or during antiviral treatment. Treatment with currently available antivirals blocking intracellular replication of HBV allows controlling of high viremia and improving liver health during long-term therapy of patients with chronic hepatitis B (CHB), but they are not sufficient to cure the disease. New therapy options that cover all HBV genotypes and emerging viral variants will have to be developed soon. In addition to the antiviral treatment of chronically infected patients, continued efforts to expand the global coverage of the currently available HBV vaccine will be one of the key factors for controlling the rising global spread of HBV. Certain improvements of the vaccine (e.g. inclusion of PreS domains) could counteract known problems such as low or no responsiveness of certain risk groups and waning anti-HBs titers leading to occult infections, especially with HBV genotypes E or F. But even with an optimal vaccine and a cure for hepatitis B, global eradication of HBV would be difficult to achieve because of an existing viral reservoir in primates and bats carrying closely related hepadnaviruses with zoonotic potential.

Update of the current knowledge on genetics, evolution, immunopathogenesis, and transmission for coronavirus disease 19 (COVID-19)

In December 2019, an acute respiratory disease caused by novel species of coronavirus (SARS-CoV-2), emerged in China and has spread throughout the world. On 11th March 2020, the World Health Organization (WHO) officially declared coronavirus disease 19 (COVID-19) a pandemic, severe coronavirus-mediated human disease. Based on genomic and phylogenetic studies, SARS-CoV-2 might originate from bat coronaviruses and infects humans directly or through intermediate zoonotic hosts. However, the exact origin or the host intermediate remains unknown. Genetically, SARS-CoV-2 is similar to several existing coronaviruses, particularly SARS-CoV, but differs by silent and non-silent mutations. The virus uses different transmission routes and targets cells and tissues with angiotensin-converting enzyme 2 (ACE2) protein, which makes it contagious. COVID-19 shares both the main clinical features and excessive/dysregulated cell responses with the two previous Middle East respiratory syndrome coronavirus (MERS) and severe acute respiratory syndrome coronavirus (SARS) epidemics. In this review, we provide an update of the current knowledge on the COVID-19 pandemic. Gaining a deeper understanding of SARS-CoV-2 structure, transmission routes, and molecular responses, will assist in the prevention and control of COVID-19 outbreaks in the future.

Cross-species transmission of the newly identified coronavirus 2019-nCoV

The current outbreak of viral pneumonia in the city of Wuhan, China, was caused by a novel coronavirus designated 2019‐nCoV by the World Health Organization, as determined by sequencing the viral RNA genome. Many initial patients were exposed to wildlife animals at the Huanan seafood wholesale market, where poultry, snake, bats, and other farm animals were also sold. To investigate possible virus reservoir, we have carried out comprehensive sequence analysis and comparison in conjunction with relative synonymous codon usage (RSCU) bias among different animal species based on the 2019‐nCoV sequence. Results obtained from our analyses suggest that the 2019‐nCoV may appear to be a recombinant virus between the bat coronavirus and an origin‐unknown coronavirus. The recombination may occurred within the viral spike glycoprotein, which recognizes a cell surface receptor. Additionally, our findings suggest that 2019‐nCoV has most similar genetic information with bat coronovirus and most similar codon usage bias with snake. Taken together, our results suggest that homologous recombination may occur and contribute to the 2019‐nCoV cross‐species transmission.

Taken together, our results suggest that homologous recombination may occur and contribute to the 2019‐nCoV cross‐species transmission.

SPECTRE: a suite of phylogenetic tools for reticulate evolution

Summary

Split-networks are a generalization of phylogenetic trees that have proven to be a powerful tool in phylogenetics. Various ways have been developed for computing such networks, including split-decomposition, NeighborNet, QNet and FlatNJ. Some of these approaches are implemented in the user-friendly SplitsTree software package. However, to give the user the option to adjust and extend these approaches and to facilitate their integration into analysis pipelines, there is a need for robust, open-source implementations of associated data structures and algorithms. Here, we present SPECTRE, a readily available, open-source library of data structures written in Java, that comes complete with new implementations of several pre-published algorithms and a basic interactive graphical interface for visualizing planar split networks. SPECTRE also supports the use of longer running algorithms by providing command line interfaces, which can be executed on servers or in High Performance Computing environments.

Availability and implementation

Full source code is available under the GPLv3 license at: https://github.com/maplesond/SPECTRE. SPECTRE's core library is available from Maven Central at: https://mvnrepository.com/artifact/uk.ac.uea.cmp.spectre/core. Documentation is available at: http://spectre-suite-of-phylogenetic-tools-for-reticulate-evolution.readthedocs.io/en/latest/.

Contact

sarah.bastkowski@earlham.ac.uk.

Supplementary information

Supplementary data are available at Bioinformatics online.

Characterization of hepatitis B virus with complex structural variations

BACKGROUND

Hepatitis B virus (HBV) infection is one of the most serious public health issues. Recent HBV genetic research has revealed novel genetic rearrangements termed complex structural variations (SVs), which are composed of combinations of SVs such as insertions, deletions, and duplications. An extensive search was made for complex SVs of HBV and their characteristics were analyzed.

RESULTS

Fifty-five HBV strains with complex SVs were identified by analyzing genetic sequences of HBV with bioinformatical tools. Along with 15 HBV strains with complex SVs in a previous report, a total of 70 HBV strains harboring complex SVs were analyzed. Complex SVs in the HBV genome were located frequently between nt 1500 and 2000. Insertions were observed in 65/70 (92.9%) of HBV strains with complex SVs. As insertional motif sequences, hepatocyte nuclear factor 1 binding site, a sequence complementary to part of box α in enhancer II, and insertions of unknown origins were observed. The complex SVs were classified into six groups, and combination of insertion and deletion was observed more frequently than other patterns.

CONCLUSION

Through an extensive search of HBV sequences, new strains with complex SVs were identified in this study. Characteristics of HBV with complex SVs were clarified by the analysis of 70 HBV strains harboring complex SVs. Further investigation is required to elucidate its role in pathogenesis of HBV-related liver disease.

Mutation and recombination in pathogen evolution: Relevance, methods and controversies

Mutation and recombination drive the evolution of most pathogens by generating the genetic variants upon which selection operates. Those variants can, for example, confer resistance to host immune systems and drug therapies or lead to epidemic outbreaks. Given their importance, diverse evolutionary studies have investigated the abundance and consequences of mutation and recombination in pathogen populations. However, some controversies persist regarding the contribution of each evolutionary force to the development of particular phenotypic observations (e.g., drug resistance). In this study, we revise the importance of mutation and recombination in the evolution of pathogens at both intra-host and inter-host levels. We also describe state-of-the-art analytical methodologies to detect and quantify these two evolutionary forces, including biases that are often ignored in evolutionary studies. Finally, we present some of our former studies involving pathogenic taxa where mutation and recombination played crucial roles in the recovery of pathogenic fitness, the generation of interspecific genetic diversity, or the design of centralized vaccines. This review also illustrates several common controversies and pitfalls in the analysis and in the evaluation and interpretation of mutation and recombination outcomes.

Novel non-canonical genetic rearrangements termed "complex structural variations" in HBV genome

BACKGROUNDS AND AIMS

Chronic hepatitis B virus (HBV) infection is an important worldwide public health issue. Further knowledge on the characteristics of HBV will facilitate its eradication. Genome structural variations (SVs) are defined by its canonical form such as duplication, deletion, and insertion. However, recent studies have reported complex SVs that cannot be explained by those canonical SVs. A HBV strain (UK2) with an unusual genome structure rearrangement that was completely different from known mutations or rearrangements was previously reported. Thus, this study was conducted to confirm the rearrangement in UK2 as a novel complex SV, and to find additional HBV strains with complex SVs. Further, the contribution of complex SVs in hepadnavirus variability was investigated.

METHODS

The genome rearrangement pattern in UK2 was analyzed. Further, a search of online databases retrieved additional HBV strains which were candidates to harbor complex SVs. The architecture of each rearrangement in the candidate strains was analyzed by bioinformatical tools. In addition, alignment of woolly monkey hepatitis virus (WMHV) and HBV from human and non-human primates was performed to investigate the contribution of complex SVs to variability of hepadnavirus.

RESULTS

The rearrangement in UK2 was confirmed as a complex SV. An additional 15 HBV strains were retrieved from databases, and confirmed as harboring complex SVs. Complex combinations of deletion, insertion, and duplication characterized the novel rearrangements. The complex SVs in six strains (37.5%) were composed of deletion, insertion, and duplication. The complex SVs in another six strains (37.5%) consisted of deletion and insertion, followed by insertions and duplication in three strains (18.8%), and deletion and duplication in one strain (6.3%). In addition, unique preS1 promoter insertions, which contained the hepatocyte nuclear factor 1 binding site, were observed in seven (43.8%) of 16 strains. Further, analysis of the genetic sequences of WMHV and HBV from human and non-human primates showed that complex combinations of deletions and insertions accounted for their genetic differences.

CONCLUSIONS

Non-canonical genetic rearrangements termed complex SVs were observed in HBV. Further, complex SVs accounted for the genetic differences of WMHV and HBV from human and non-human primates.

TriLoNet: Piecing Together Small Networks to Reconstruct Reticulate Evolutionary Histories

Phylogenetic networks are a generalization of evolutionary trees that can be used to represent reticulate processes such as hybridization and recombination. Here, we introduce a new approach called TriLoNet (Trinet Level- one Network algorithm) to construct such networks directly from sequence alignments which works by piecing together smaller phylogenetic networks. More specifically, using a bottom up approach similar to Neighbor-Joining, TriLoNet constructs level-1 networks (networks that are somewhat more general than trees) from smaller level-1 networks on three taxa. In simulations, we show that TriLoNet compares well with Lev1athan, a method for reconstructing level-1 networks from three-leaved trees. In particular, in simulations we find that Lev1athan tends to generate networks that overestimate the number of reticulate events as compared with those generated by TriLoNet. We also illustrate TriLoNet's applicability using simulated and real sequence data involving recombination, demonstrating that it has the potential to reconstruct informative reticulate evolutionary histories. TriLoNet has been implemented in JAVA and is freely available at https://www.uea.ac.uk/computing/TriLoNet.

Early mesozoic coexistence of amniotes and hepadnaviridae

Hepadnaviridae are double-stranded DNA viruses that infect some species of birds and mammals. This includes humans, where hepatitis B viruses (HBVs) are prevalent pathogens in considerable parts of the global population. Recently, endogenized sequences of HBVs (eHBVs) have been discovered in bird genomes where they constitute direct evidence for the coexistence of these viruses and their hosts from the late Mesozoic until present. Nevertheless, virtually nothing is known about the ancient host range of this virus family in other animals. Here we report the first eHBVs from crocodilian, snake, and turtle genomes, including a turtle eHBV that endogenized >207 million years ago. This genomic “fossil” is >125 million years older than the oldest avian eHBV and provides the first direct evidence that Hepadnaviridae already existed during the Early Mesozoic. This implies that the Mesozoic fossil record of HBV infection spans three of the five major groups of land vertebrates, namely birds, crocodilians, and turtles. We show that the deep phylogenetic relationships of HBVs are largely congruent with the deep phylogeny of their amniote hosts, which suggests an ancient amniote–HBV coexistence and codivergence, at least since the Early Mesozoic. Notably, the organization of overlapping genes as well as the structure of elements involved in viral replication has remained highly conserved among HBVs along that time span, except for the presence of the X gene. We provide multiple lines of evidence that the tumor-promoting X protein of mammalian HBVs lacks a homolog in all other hepadnaviruses and propose a novel scenario for the emergence of X via segmental duplication and overprinting of pre-existing reading frames in the ancestor of mammalian HBVs. Our study reveals an unforeseen host range of prehistoric HBVs and provides novel insights into the genome evolution of hepadnaviruses throughout their long-lasting association with amniote hosts.

Viruses are not known to leave physical fossil traces, which makes our understanding of their evolutionary prehistory crucially dependent on the detection of endogenous viruses. Ancient endogenous viruses, also known as paleoviruses, are relics of viral genomes or fragments thereof that once infiltrated their host's germline and then remained as molecular “fossils” within the host genome. The massive genome sequencing of recent years has unearthed vast numbers of paleoviruses from various animal genomes, including the first endogenous hepatitis B viruses (eHBVs) in bird genomes. We screened genomes of land vertebrates (amniotes) for the presence of paleoviruses and identified ancient eHBVs in the recently sequenced genomes of crocodilians, snakes, and turtles. We report an eHBV that is >207 million years old, making it the oldest endogenous virus currently known. Furthermore, our results provide direct evidence that the Hepadnaviridae virus family infected birds, crocodilians and turtles during the Mesozoic Era, and suggest a long-lasting coexistence of these viruses and their amniote hosts at least since the Early Mesozoic. We challenge previous views on the origin of the oncogenic X gene and provide an evolutionary explanation as to why only mammalian hepatitis B infection leads to hepatocellular carcinoma.

Resolving ambiguity in the phylogenetic relationship of genotypes A, B, and C of hepatitis B virus

Background

Hepatitis B virus (HBV) is an important infectious agent that causes widespread concern because billions of people are infected by at least 8 different HBV genotypes worldwide. However, reconstruction of the phylogenetic relationship between HBV genotypes is difficult. Specifically, the phylogenetic relationships among genotypes A, B, and C are not clear from previous studies because of the confounding effects of genotype recombination. In order to clarify the evolutionary relationships, a rigorous approach is required that can effectively explore genetic sequences with recombination.

Result

In the present study, phylogenetic relationship of the HBV genotypes was reconstructed using a consensus phylogeny of phylogenetic trees of HBV genome segments. Reliability of the reconstructed phylogeny was extensively evaluated in agreements of local phylogenies of genome segments.

The reconstructed phylogenetic tree revealed that HBV genotypes B and C had a closer phylogenetic relationship than genotypes A and B or A and C. Evaluations showed the consensus method was capable to reconstruct reliable phylogenetic relationship in the presence of recombinants.

Conclusion

The consensus method implemented in this study provides an alternative approach for reconstructing reliable phylogenetic relationships for viruses with possible genetic recombination. Our approach revealed the phylogenetic relationships of genotypes A, B, and C of HBV.

Avihepadnavirus diversity in parrots is comparable to that found amongst all other avian species

Avihepadnaviruses have previously been isolated from various species of duck, goose, stork, heron and crane. Recently the first parrot avihepadnavirus was isolated from a Ring-necked Parakeet in Poland. In this study, 41 psittacine liver samples archived in Poland over the last nine years were tested for presence of Parrot hepatitis B virus (PHBV). We cloned and sequenced PHBV isolates from 18 birds including a Crimson Rosella, an African grey parrot and sixteen Ring-necked Parakeets. PHBV isolates display a degree of diversity (>78% genome wide pairwise identity) that is comparable to that found amongst all other avihepadnaviruses (>79% genome wide pairwise identity). The PHBV viruses can be subdivided into seven genetically distinct groups (tentatively named A-G) of which the two isolated of PHBV-G are the most divergent sharing ∼79% genome wide pairwise identity with all their PHBVs. All PHBV isolates display classical avihepadnavirus genome architecture.

Hepatitis B virus with a proposed genotype I was found in Sichuan Province, China

To date, eight hepatitis B virus (HBV) genotypes, A-H, have been designated, and two additional genotypes, I and J, have also been proposed. A serological survey targeting children in difficult-to-reach vaccination areas was carried out in remote counties of Sichuan Province, China. HBV genotypes and serotypes were also determined from HBsAg-positive serum samples by direct sequencing. Phylogenetic analysis showed two strains isolated from the Yi ethnic children clustered with the proposed genotype I. The pairwise genome genetic distance was 7.5% between genotypes I and C, and ranged from 8.4% to 15.2% between genotype I and other genotypes, except genotype C. Grouping Scan analyses of the two strains revealed apparent recombination events between an unknown genotype and genotype C. Two out of four HBV strains isolated from the Yi ethnic children were confirmed to be genotype I, suggesting widespread circulation and common infection with genotype I HBV in the local Yi population. High prevalence of HBsAg and low hepatitis B vaccination coverage indicated that additional efforts are needed to control HBV infection in those areas.

Species association of hepatitis B virus (HBV) in non-human apes; evidence for recombination between gorilla and chimpanzee variants

Hepatitis B virus (HBV) infections are widely distributed in humans, infecting approximately one third of the world's population. HBV variants have also been detected and genetically characterised from Old World apes; Gorilla gorilla (gorilla), Pan troglodytes (chimpanzee), Pongo pygmaeus (orang-utan), Nomascus nastusus and Hylobates pileatus (gibbons) and from the New World monkey, Lagothrix lagotricha (woolly monkey). To investigate species-specificity and potential for cross species transmission of HBV between sympatric species of apes (such as gorillas and chimpanzees in Central Africa) or between humans and chimpanzees or gorillas, variants of HBV infecting captive wild-born non-human primates were genetically characterised. 9 of 62 chimpanzees (11.3%) and two from 11 gorillas (18%) were HBV-infected (15% combined frequency), while other Old world monkey species were negative. Complete genome sequences were obtained from six of the infected chimpanzee and both gorillas; those from P. t .ellioti grouped with previously characterised variants from this subspecies. However, variants recovered from P. t. troglodytes HBV variants also grouped within this clade, indicative of transmission between sub-species, forming a paraphyletic clade. The two gorilla viruses were phylogenetically distinct from chimpanzee and human variants although one showed evidence for a recombination event with a P.t.e.-derived HBV variant in the partial X and core gene region. Both of these observations provide evidence for circulation of HBV between different species and sub-species of non-human primates, a conclusion that differs from the hypothesis if of strict host specificity of HBV genotypes.

A high variability of mixed infections and recent recombinations of hepatitis B virus in Laos

In Lao PDR, where more than 8% of the population are chronic carriers of HBsAg, multiple genotypes and subgenotypes co-circulate and are prone to generate recombinant viruses. Phylogenetic analyses of multiple clones per donor revealed mixed infections of subgenotypes B1, B2, B4, C1, C5, I1 and I2 in almost 6% of HBsAg positive rejected blood donors. Recombination analyses and distance calculations furthermore showed that about 65% (17/26) of the mixed infected donors showed recombinations in the S-gene alone, involving the predominant genotypes B and C. These results suggest that, at least in Laos, hepatitis B virus (HBV) mixed infections lead to frequent recombinations. In many donors with recombinant strains, the recombinant fragment and a non-recombinant strain of the same genotype co-existed (127/185 analysed recombinant fragments). For a large proportion of these (60/127), the most closely related known virus was found, although not always exclusively, in the same donor. Recombinant virus strains are largely distinct. This is reflected in an unexpected diversity in recombination breakpoints and the relatively rare recombinations with identical recombination patterns of the same genotypes in different donors. Recent recombination events would explain the limited spread of each of the recombinants. Using a published mutation rate of 4.2×10⁻⁵ mutations per site and year, the observed minimum genetic distances of 0–0.60% between parent strain and recombinant fragment would correspond to 0–71 years of evolution from a most recent common ancestor (MRCA). Thus several lines of evidence are suggestive of recent independent recombination events, a proportion of these even occurring within the same donors. In conclusion, our analyses revealed a high variability of mixed infections as a very probable breeding ground of multiple variable recombination events in Laos that so far have not led to new dominant strains.

Evaluation of intra-host variants of the entire hepatitis B virus genome

Genetic analysis of hepatitis B virus (HBV) frequently involves study of intra-host variants, identification of which is commonly achieved using short regions of the HBV genome. However, the use of short sequences significantly limits evaluation of genetic relatedness among HBV strains. Although analysis of HBV complete genomes using genetic cloning has been developed, its application is highly labor intensive and practiced only infrequently. We describe here a novel approach to whole genome (WG) HBV quasispecies analysis based on end-point, limiting-dilution real-time PCR (EPLD-PCR) for amplification of single HBV genome variants, and their subsequent sequencing. EPLD-PCR was used to analyze WG quasispecies from serum samples of patients (n = 38) infected with HBV genotypes A, B, C, D, E and G. Phylogenetic analysis of the EPLD-isolated HBV-WG quasispecies showed the presence of mixed genotypes, recombinant variants and sub-populations of the virus. A critical observation was that HBV-WG consensus sequences obtained by direct sequencing of PCR fragments without EPLD are genetically close, but not always identical to the major HBV variants in the intra-host population, thus indicating that consensus sequences should be judiciously used in genetic analysis. Sequence-based studies of HBV WG quasispecies should afford a more accurate assessment of HBV evolution in various clinical and epidemiological settings.

Identification of four novel subgenotypes (C13-C16) and two inter-genotypic recombinants (C12/G and C13/B3) of hepatitis B virus in Papua province, Indonesia

Four novel subgenotypes (C6, C11, C12, and D6) of hepatitis B virus (HBV) were identified in Papua, a multiethnic province of Indonesia. To characterize the HBV strains in Papua, serum samples collected from 515 indigenous inhabitants (mean age: 26.6±9.6 years) in a previously unexamined area, Nabire, located in northern Papua, were used in the present study. Among 46 samples whose 1.6-kilobase (kb) HBV DNA sequence was amplified, 38 (83%) were typeable into known subgenotypes [B3 (n=4), C1 (n=2), C5, (n=1), C6 (n=5), C12 (n=13), and D6 (n=13)]. An analysis of the full-length sequence of the eight remaining HBV/C isolates whose sequence was either unclassifiable or uncertain within the 1.6-kb sequence showed no significant evidence of recombination in six isolates, and inter-genotypic recombination in two isolates (NAB20 and NAB46). By pairwise comparisons and a maximum-likelihood phylogenetic analysis, six non-recombinant isolates were considered significantly remote from known HBV/C isolates of subgenotypes C1-C12, and were classifiable into four novel subgenotypes (tentatively designated C13-C16). NAB20 and NAB46 were hybrids of C13/B3 and C12/G, respectively, displaying recombination breakpoints in the 5'-terminus of the P gene. Notably, the distribution of presumably indigenous subgenotypes C11-C16 was associated with particular language speakers in Papua.

Hepatitis B virus (HBV) X gene diversity and evidence of recombination in HBV/HIV co-infected persons

The high frequency of mutation during hepatitis B virus (HBV) infection has resulted in 8 genotypes (A-H) with varying effects on disease severity and treatment efficacy. However, analysis of intrapatient HBV diversity is limited, especially during HIV co-infection. Therefore, a preliminary study was performed to analyze HBV X gene diversity in 17 HBV/HIV co-infected individuals. Phylogenetic analysis revealed HBV genotype A in 13 individuals (76.5%) or genotype E in 1 individual (5.9%). Additionally, 3 individuals were dually infected with HBV genotypes A and G (17.6%). Overall, higher genetic distance and entropy were observed in the X region and overlapping polymerase (Pol(X)) regions when compared to the PreS, S, and overlapping polymerase (Pol(PS) and Pol(S)) regions analyzed in the same patients as part of a previous study. In addition, multiple viral variants from 2 individuals with dual HBV infection did not group with either genotype A or G by phylogenetic analysis, indicating possible recombination. SimPlot bootscan analysis confirmed recombination breakpoints within the X gene in both individuals. Recombination between HBV genotypes may represent an important evolutionary strategy that enhances overall pathogenic potential and/or alters the downstream effects of the HBV X protein.

A complex hepatitis B virus (X/C) recombinant is common in Long An county, Guangxi and may have originated in southern China

Recently, a complex (X/C) hepatitis B virus (HBV) recombinant, first reported in 2000, was proposed as a new genotype; although this was refuted immediately because the strains differ by less than 8 % in nucleotide distance from genotype C. Over 13.5 % (38/281) of HBV isolates from the Long An cohort in China were not assigned to a specific genotype, using current genotyping tools to analyse surface ORF sequences, and these have about 98 % similarity to the X/C recombinants. To determine whether this close identity extends to the full-length sequences and to investigate the evolutionary history of the Long An X/C recombinants, 17 complete genome sequences were determined. They are highly similar (96–99 %) to the Vietnamese strains and, although some reach or exceed 8 % nucleotide sequence difference from all known genotypes, they cluster together in the same clade, separating in a phylogenetic tree from the genotype C branch. Analysis of recombination reveals that all but one of the Long An isolates resembles the Vietnamese isolates in that they result from apparent recombination between genotype C and a parent of unknown genotype (X), which shows similarity in part to genotype G. The exception, isolate QL523, has a greater proportion of genotype C parent. Phylogeographic analysis reveals that these recombinants probably arose in southern China and spread later to Vietnam and Laos.

Do we need to determine viral genotype in treating chronic hepatitis B?

Many studies have attested that not only does HBV genotype influence the outcome of the disease but it also influences the outcome of therapy with interferons and pegylated interferons, with genotype A doing better than genotype D in Caucasians and genotype B better than genotype C in Asians. However, the guidelines from three regional bodies - AASLD, APASL and EASL - all stop short of recommending genotyping as part of the management of chronic hepatitis B. The recommendations, however, from several national organizations as well as from individual reviewers suggest that genotyping is essential to detect patients in whom the use of pegylated interferon will give a high likelihood of response with a finite course of therapy and avoid the disadvantages of nucleoside analogues with their viral resistance. It is concluded that determination of HBV genotype should form part of the management in treating chronic hepatitis B.

Molecular characterization of hepatitis B virus and a 9-year clinical profile in a patient infected with genotype I

An unusual hepatitis B virus (HBV) variant, assigned provisionally to genotype I, was recently reported, characterized by an anomalous genotyping pattern and putative recombination; however, the natural history of this unusual strain is unknown. This study analyzed longitudinal sera collected over a 9-year period from a patient infected with this variant to investigate the clinical profile and intrahost viral evolution over time. The patient, who had immigrated to Canada in 1998 from Vietnam, was treated with lamivudine in 2000. Approximately 4-5 years following the withdrawal of lamivudine therapy, a genomic "shift" occurred coincident with ALT flares and increasing HBV viral load, resulting in numerous stable nucleotide substitutions within the core coding region, suggesting altered immune control that may provide a selective advantage to the virus. Analysis of quasispecies diversity over time demonstrated further this shift, with two sequence clusters associated with time points either prior to or following relapse observed, including increased diversity among quasispecies prior to relapse. In keeping with the complex nature of genotype I strains, majority population genomes had a mean genetic distance from genotype C of 7.6 +/- 0.1%, although large genomic segments lacked significant homology with any HBV genotype. Further study is needed to understand the evolutionary origin and natural history of infection with this unique HBV variant.

A novel hepatitis B virus (HBV) subgenotype D (D8) strain, resulting from recombination between genotypes D and E, is circulating in Niger along with HBV/E strains

Niger is a west African country that is highly endemic for hepatitis B virus (HBV) infection. The seroprevalence for HBV surface antigen (HBsAg) is about 20%; however, there are no reports on the molecular epidemiology of HBV strains spreading in Niger. In the present study, HBV isolates from the sera of 58 consecutive, asymptomatic, HBsAg-positive blood donors were characterized. Genotype affiliation was determined by amplification, sequencing and phylogenetic analysis of the preS1, polymerase/reverse transcriptase (RT/Pol) and precore (preC)/C regions. The first series of results revealed that different genomic fragments clustered with different genotypes on phylogenetic trees, suggesting recombination events. Twenty-four complete genomic sequences were obtained by amplification and sequencing of seven overlapping regions covering the whole genome, and were studied by extensive phylogenetic analysis. Among them, 20 (83.3%) were classified unequivocally as genotype E (HBV/E). The remaining four (16.7%) clustered on a distinct branch within HBV/D with strong bootstrap and posterior probability values. Complete molecular characterization of these four strains was achieved by the Simplot program, bootscanning analysis and cloning experiments, and enabled us to identify an HBV/D-E recombinant that formed a new HBV/D subgenotype spreading in Niger, tentatively named D8. Moreover, 20 new complete HBV/E nucleotide sequences were determined that exhibited higher genetic variability than is generally described in Africa. One was found to be a recombinant containing HBV/D sequences in the preS2 and RT/Pol regions. Taken together, these data suggest that, in Niger, genetic variability of HBV strains is still evolving, probably reflecting ancient endemic HBV infection.

Identification of natural recombination in duck hepatitis B virus

Due to its high similarity to human hepatitis B virus (HBV), duck HBV (DHBV) is often used as an important model for HBV research. While inter-genotypic recombination of HBV is common, it has not been reported with DHBV. In this study, 32 non-redundant DHBV complete genomes were analyzed using phylogenetic methods and classified into two clusters, corresponding to the 'Chinese' and 'Western country' branches previously reported based on geographical distribution. One 'Chinese' branch strain was isolated in Australia and three 'Western country' branch strains were isolated in China, suggesting cross-geographical distribution of both branches. Recombination analyses of the 32 DHBV genomes identified two possible inter-genotypic recombination events with high confidence value. These recombination events occurred between the lineages represented, respectively, by the Chinese isolate GD3 (AY536371, 'Chinese' branch) and the American isolate DHBV16 (K01834, 'Western country' branch), giving rise to two Chinese recombinant isolates CH4 (EU429324) and CH6 (EU429326). The identification of inter-genotypic recombination among circulating DHBV isolates suggests the usefulness of DHBV as a model for studying the mechanism of HBV recombination.

Geographical and genetic diversity of the human hepatitis B virus

Hepatitis B virus (HBV) is one of the most widely distributed viruses that infect humankind. Distinct clinical and virological characteristics of the HBV-infection have been reported in different geographical parts of the world and are increasingly associated with genetic diversity of the infecting virus. HBV is classified into genotypes and subgenotypes that are associated with ethnicity and geography. The genetic diversity of HBV in its various aspects has been the subject of extensive investigations during the last few decades. Since molecular epidemiology research tools have become widely available, the number of new publications in this field has grown exponentially. This review summarises the recent publications on the geographical distribution of genetic variants of HBV, and proposes updated criteria for the identification of new genotypes and subgenotypes of the virus.

Worldwide genetic diversity of HBV genotypes and risk of hepatocellular carcinoma

Hepatitis B viruses (HBV) are responsible for over 50% of the worldwide attributable risk of hepatocellular carcinoma (HCC) and this figure increases even further in regions of high endemicity. Systematic sequencing of HBV genomes has identified that this common virus existed as eight distinct genotypes (denoted A-H), each regrouping variants with less than 8% divergence in their DNA sequence. These genotypes differ by their geographic distribution in populations around the globe. There is evidence that HBV genotypes also differ by their pathogenic properties, including their risk of persistence as chronic infection and their capacity to induce precursor disease or cancer. On the other hand, HBV genes may undergo mutations that become selected during the course of chronic infection and progressive liver disease. The most significant of these mutations in the context of HCC are those occurring in the pre-core (Pre-C) and basal core promoter (BCP) regions. These mutations may upregulate HBV expression and increase its virulence. These mutations may occur in all HBV genotypes but are more common in genotypes associated with more severe disease and cancer, in particular genotype C. Understanding the molecular basis of pathological variations between HBV variants is critical for prediction of disease severity. It will also be important to determine whether differences among genotypes may have an impact on the long-term protective efficacy of universal HBV vaccination.

Deletions and recombinations in the core region of hepatitis B virus genotype E strains from asymptomatic blood donors in Guinea, west Africa

The prevalence of hepatitis B virus (HBV) surface antigen (HBsAg) chronic carriage in west Africa is the highest in the world, but its molecular epidemiology remains relatively poorly investigated. Plasma samples from random asymptomatic carriers of HBsAg in Conakry, Guinea, were studied and the complete genome sequences of 81 strains were obtained. Three additional samples from Kumasi, Ghana, were also included in the analysis. Phylogenetic analyses confirmed the dominance of genotype E (95.1%), including 8.6% of strains (viral load, 5x10(3)-2.6x10(8) IU ml(-1)) comprising dominant variants with large deletions in the core region and minority wild-type variants. The presence of two different patterns of deletions in two and four donors suggested targeted genome fragility between nt 1979 and 2314. The remaining sequences included one subgenotype A3 (1%) and six A/E recombinant forms (4-7%). A/E strains with identical points of recombination in three donors suggested strongly that these recombinant HBV strains are circulating and transmitted in the population. Recombination points were concentrated in the core gene. The detection of similar A/E recombinant strains in Ghana suggested a geographical extension of recombinant HBV to the region. The quasispecies of one additional Ghanaian strain sequenced in the pre-surface/surface region resolved into dominant clones of either the A or E genotype, but also three different patterns of A/E recombinant variants. The observation that both deletions of genotype E strains and A/E recombination points are mostly located in the core gene at specific positions indicates a region of the genome where genetic rearrangements preferentially take place.

Coinfection rates in Φ6 bacteriophage are enhanced by virus-induced changes in host cells

Two or more viruses infecting the same host cell can interact in ways that profoundly affect disease dynamics and control, yet the factors determining coinfection rates are incompletely understood. Previous studies have focused on the mechanisms that viruses use to suppress coinfection, but recently the phenomenon of enhanced coinfection has also been documented. In the experiments described here, we explore the hypothesis that enhanced coinfection rates in the bacteriophage Φ6 are achieved by virus-induced upregulation of the Φ6 receptor, which is the bacterial pilus. First, we confirmed that coinfection enhancement in Φ6 is virus-mediated by showing that Φ6 attaches significantly faster to infected cells than to uninfected cells. Second, we explored the hypothesis that coinfection enhancement in Φ6 depends upon changes in the expression of an inducible receptor. Consistent with this hypothesis, the closely related phage, Φ12, that uses constitutively expressed lipopolysaccharide as its receptor, attaches to infected and uninfected cells at the same rate. Our results, along with the previous finding that coinfection in Φ6 is limited to two virions, suggest that viruses may closely regulate rates of coinfection through mechanisms for both coinfection enhancement and exclusion.

Identification and characterization of genotype A and D recombinant hepatitis B virus from Indian chronic HBV isolates

AIM: To confirm the presence of recombination, full-length hepatitis B virus (HBV) from chronic patients was sequenced and analyzed.

METHODS: Full-length HBV genomes from 12 patients were amplified and sequenced in an automated sequencer. Phylogenetic analysis was carried out on full-length, Core and preS2/Surface regions using MEGA software. SimPlot Boot Scanning and amino acid sequence analysis were performed for confirmation of recombination.

RESULTS: Eight patients were infected with genotype D strain; one patient with genotype A and three patients had genotype A and D recombination; two of them had cirrhosis and one had hepatocellular carcinoma. Phylogenetic analysis of core and preS2/surface regions separately showed evidence of genotype A and D recombination. The breakpoints of recombination were found to be at the start of preS2 and at the end of surface coding regions.

CONCLUSION: We identified and characterized recombinant A and D genotype HBV in hepatitis B surface antigen (HBsAg)-positive patients.

Japanese case of hepatitis B virus genotypes C/D hybrid

Hepatitis B virus (HBV) is classified into eight genotypes based on complete genome sequence. Each genotype is related to geographic distribution and race. In Japan, most of the genotypes are B and C. In the present study, we report the first Japanese strain of HBV having a recombination between genotypes C and D. A 30-year-old woman was admitted to Kobe Medical Center because of liver dysfunction. She was diagnosed with spontaneous reactivation of chronic hepatitis B. She had no history of blood transfusion and her parents were negative for HBV. The phylogenetic analysis based on the complete genome sequences revealed that this strain was classified into genotype C, whereas the analysis based on Sgene sequence showed that this strain was genotype D. By using a SimPlot program, this strain was confirmed as a recombinant strain between genotypes C and D. Compared with previous recombinant strains in China, the breakpoint was the same and the difference was only 0.8% of the complete genome sequence. It was unclear whether or not this strain was transmitted from China, but the recombinant strains and intergenotypes of HBV have already existed in Japan.

Bayesian estimates of the evolutionary rate and age of hepatitis B virus

Accurately estimating the evolutionary rate and age of hepatitis B virus (HBV) has proven to be one of the most difficult problems in studies of viral evolution. To help resolve these issues we employed a recently developed Bayesian coalescent approach to globally sampled human and avian hepadnavirus genome sequences, accounting for lineage-specific rate variation, the presence of overlapping reading frames, and the potential impact of recombination. Our analysis revealed an unexpectedly high rate of evolutionary change--up to 10(-4) nucleotide substitutions (subs) per site per year and always more than approximately 10(-6) subs/site/year. These rates suggested a time to the most recent common ancestor (tMRCA) of the sampled isolates of consistently less than approximately 1500 years ago for human HBV and less than 6000 years ago for the avian hepadnaviruses. Notably, the evolutionary rate of nonoverlapping regions of the viral genome was approximately 2-fold greater than that of overlapping genome regions, reflecting the complex patterns of selective constraint inherent in the former. We also reveal that most recombination events in both human and avian HBV tend to fall in a specific region of the viral genome, which contains all four viral open reading frames and which may therefore represent a "hot spot" for recombination. However, while recombination affects estimates of both evolutionary rate and tMRCA, in no case was this sufficient to challenge the hypothesis that the dominant mode of HBV evolution is by recent cross-species transmission. We conclude that HBV exhibits rapid evolutionary dynamics, typical of other viruses dependent on reverse transcriptase-mediated replication.

No significant differences in histology and response to interferon treatment in hepatitis B carriers of genotypes C and recombinant B

Hepatitis B virus (HBV) genotypes B and C are most prevalent in China and genotype B is found exclusively in recombination with the pre-C/C gene of genotype C. We investigated whether there is a difference in clinical relevance between the two genotypes sharing the same pre-C/C gene. Thus, we determined the genotype of HBV among consecutive HBeAg-positive patients with tailored interferon-alpha (IFN-alpha) therapy, and the demographic, baseline clinical characteristics and treatment results were compared between them. The median values of alanine transaminase (ALT) were 4.5 and 5.0 times the upper limit of normal (P = 0.419), HBV-DNA levels were 1.4 x 10(7) and 1.5 x 10(7)copies/mL (P = 0.829), mean scores of necroinflammatory histological activity 9.8 and 10.44 (P = 0.105) and fibrotic activity 2.64 and 2.86 (P = 0.227) in genotype B and C patients, respectively. The end-of-treatment response was 42.7% and 39.0% (P = 0.531) with mean tailored treatment months of 8.28 and 9.34 (P = 0.160), and the sustained response 43.4% and 37.5% (P = 0.31) at the end of a 12-month follow-up period in genotype B and C patients, respectively. These results remained similar when follow-up was extended to nearly 3 years. In conclusion, no significant differences in clinical characteristics and response to IFN-alpha between genotypes B and C were found, probably, because both types shared a common pre-C/C encoding region.

Preliminary study on hepatitis B virus genotypes in Xiamen city

AIM: To investigate the genotypes of hepatitis B virus (HBV) in Xiamen city by nested polymerase chain reaction (PCR) with multiplex pairs of genotype-specific primers.

METHODS: A total of 250 HBV-infected patients were included in this study. The serum samples were collected and the serum HBV DNA was used as templates. Ten outer and inner primers were designed on the basis of nucleotide sequences in the regions of Pre-S1 and S genes, of which 8 genotype-specific inner primers were divided into 2 groups: A and B. Genotype A, B, C or D, E, F of HBV were amplified, respectively. The genotypes of the second-round PCR products were identified using agarose gel electrophoresis (30 g/L).

RESULTS: Of the 250 selected patients, 120 received the above genotyping successfully. There were 90 (75.0%) diagnosed with chronic hepatitis B, 7 (5.8%) with acute hepatitis B, 8 (6.7%) with liver cirrhosis, and 15 (12.5%) with hepatocellular carcinoma. Of the 120 cases, 58 (48.3%) were found with genotype B, 30 (25.0%) with genotype C and 32 (26.7%) with genotype B/C. In the patients with positive HBeAg, genotype B and B/C were confirmed in 63.8% and 21.9% of them, respectively. However, the patients with genotype B/C and B accounted for 68.8% and 25.9% of the anti-HBe-positive patients. There were significant differences between the 2 sub-groups in the genotype distribution (P < 0.05).

CONCLUSION: Genotype B prevails among HBV-infected patients in Xiamen city, and type B/C HBV infection a considerable problem.

High level of genetic heterogeneity in S and P genes of genotype D hepatitis B virus

The genetic heterogeneity of hepatitis B virus (HBV) genotypes and subgenotypes was investigated by directly sequencing amplified PreS, S and P genes of HBV isolates obtained from the plasma of 99 subjects with chronic HBV infection. Genotype D showed the greatest intragenotypic and intrasubgenotypic divergence: in particular, the a determinant was mutated in 58.2% of the genotype D patients, two of whom showed prototypic vaccine-induced escape mutants at codon 145. Moreover, five sites under significant positive selection were found in the S protein of the D isolates: one in the a determinant and four in the highly hydrophobic C terminal. Our results suggest that careful surveillance of vaccine-induced escape mutants should be considered in populations with highly frequent genotype D infections, and raise questions concerning the possible relationship between the genetic heterogeneity, host immunity and pathogenicity of this HBV genotype.

Quasispecies and its impact on viral hepatitis

Quasispecies dynamics mediates adaptability of RNA viruses through a number of mechanisms reviewed in the present article, with emphasis on the medical implications for the hepatitis viruses. We discuss replicative and non-replicative molecular mechanisms of genome variation, modulating effects of mutant spectra, and several modes of viral evolution that can affect viral pathogenesis. Relevant evolutionary events include the generation of minority virus variants with altered functional properties, and alterations of mutant spectrum complexity that can affect disease progression or response to treatment. The widespread occurrence of resistance to antiviral drugs encourages new strategies to control hepatic viral disease such as combination therapies and lethal mutagenesis. In particular, ribavirin may be exerting in some cases its antiviral activity with participation of its mutagenic action. Despite many unanswered questions, here we document that quasispecies dynamics has provided an interpretation of the adaptability of the hepatitis viruses, with features conceptually similar to those observed with other RNA viruses, a reflection of the common underlying Darwinian principles.

Hepatitis B virus taxonomy and hepatitis B virus genotypes

Hepatitis B virus (HBV) is a member of the hepadnavirus family. Hepadnaviruses can be found in both mammals (orthohepadnaviruses) and birds (avihepadnaviruses). The genetic variability of HBV is very high. There are eight genotypes of HBV and three clades of HBV isolates from apes that appear to be additional genotypes of HBV. Most genotypes are now divided into subgenotypes with distinct virological and epidemiological properties. In addition, recombination among HBV genotypes increases the variability of HBV. This review summarises current knowledge of the epidemiology of genetic variability in hepadnaviruses and, due to rapid progress in the field, updates several recent reviews on HBV genotypes and subgenotypes.

Identification of Hepatitis B virus putative intergenotype recombinants by using fragment typing

Eight hundred and thirty-seven human Hepatitis B virus (HBV) genomes were categorized into pure genotypes and potential intergenotypes, according to their fragment types which were determined based on similarity and phylogenetic analyses of 13 contrived fragments of 250 bp against the corresponding fragments of the consensus sequences of genotypes A-H. Twenty-five intergenotypes, including 171 genomes, were revealed from the potential intergenotype recombinants by phylogenetic analysis of the precisely derived mosaic fragments. Among these, four new intergenotypes were discovered. Many genomes were revealed as putative intergenotype recombinants for the first time. About 87 % of the putative recombinants were B/C (120) and A/D (29) hybrids. The other recombinants comprised A/B/C, A/C, A/E, A/G, C/D, C/F, C/G, C/U (U for unknown genotype) and B/C/U hybrids. Genotypes A and C showed a higher recombination tendency than did other genotypes. The results also demonstrated region priority and breakpoint hot spots in the intergenotype recombination. Recombination breakpoints were found to be concentrated mainly in the vicinity of the DR1 region (nt 1640-1900), the pre S1/S2 region (nt 3150-100), the 3'-end of the C gene (nt 2330-2450) and the 3'-end of the S gene (nt 650-830). These results support the suggestion that intergenotype recombinants may result from co-infection with different genotypes.

Detection of hepatitis B virus genotypes and mutants: current status

Characterization results of the hepatitis B virus (HBV) genome before, during and after antiviral treatment have changed in the last year for a number of reasons. First of all, with the introduction of more nucleoside and nucleotide antiviral therapies, it has become clear that variants or mutants do emerge in time. Viral genomic changes in the HBV polymerase gene can result in a direct antiviral effect, but compensatory mutations can also be identified during prolonged treatment periods. Furthermore, there is an increasing number of reports suggesting that HBV genotypes can be related to, for example, disease progression or the effect of antiviral treatment itself (alpha-interferon or lamivudine). Combined with HBV DNA viral load monitoring, an increase in viral load or a limited reduction during treatment is indicative of genomic changes related to resistance. However, these genomic changes can also be present in the absence of an increase in HBV DNA. Methodologies for the detection of these variants, as well as the determination of genotypes, are rather straightforward. Sequence analysis is time-consuming and expensive, but provides the most information, particularly if not all information on mutations related to antiviral resistance is known. However, the sensitivity of direct sequencing for the presence of minor variant populations is poor, and no mixtures of variant populations are, in general, detected. The ability to detect minor populations and, if possible, even quantify them, gives more insightful information on the dynamic evolution of the virus itself. Antiviral treatment can result in the appearance of more than one population of variants, which can be present for a prolonged period of time, and even remain undetected with current technologies. However, screening specifically for these variant populations before starting treatment for so-called untreated patients (who have received no antiviral treatment for, e.g., 6 months) has already shown that the effects of treatment can be biased. Furthermore, the detection of more dynamic viral populations - including both wild-type and resistant variants - during, but also after therapy, does provide helpful information in the analysis of virological data. Technologies enabling the detection and quantification of these variant populations are presented and discussed.

High prevalence and mapping of pre-S deletion in hepatitis B virus carriers with progressive liver diseases

BACKGROUND & AIMS

The interactions among pre-S deletion, precore (PC) mutation, and basal core promoter (BCP) mutation in various stages of chronic hepatitis B virus (HBV) infection remain unclear and were thus investigated in this study.

METHODS

The sequences of the pre-S region and the BCP (A1762T, G1764A) and PC (G1896A) mutations were determined in 46 HBV chronic carriers (CC) and 106 age-matched carriers with different stages of liver diseases, including 38 chronic hepatitis (CH), 18 cirrhosis (LC), and 50 hepatocellular carcinoma (HCC).

RESULTS

A higher prevalence of pre-S deletion and BCP and PC mutations was found in carriers with progressive liver diseases compared with the CC group. By logistic regression analysis, patients with pre-S deletion and BCP mutation were significantly associated with the development of progressive liver diseases than those without. Combination of mutations rather than single mutation was associated with the development of progressive liver diseases, especially in combination with pre-S deletion. Sequencing analysis showed that the deleted regions were more often in the 3' terminus of pre-S1 and the 5' terminus of pre-S2. Further mapping of these pre-S deletion sequences found that all the deletion regions encompassed T- and B-cell epitopes, and most of them lost 1 or more functional sites.

CONCLUSIONS

Our data indicate that patients with progressive liver diseases have a higher frequency of pre-S deletion.

Evolution of Hepatitis B virus in an acute hepatitis B patient co-infected with genotypes B and C

The interactions between different genotypes of Hepatitis B virus (HBV) in co-infected patients remain largely unknown, especially in acute infection. Here, the evolution of HBV strains was studied in an acute, self-limited hepatitis B patient co-infected with genotypes Ba (B2) and C. Virological analyses were performed at four time points after admission: T1 (5 days), T2 (11 days), T3 (22 days) and T4 (260 days). A dominant-genotype change from genotype C to Ba was found after anti-HBV e antigen (anti-HBe) seroconversion. Further clonal and phylogenetic analyses of the pre-S and pre-core/core regions of HBV were carried out to clarify the interactions between genotypes Ba and C. All clones propagated from T1 and T2 were of genotype C. In contrast, clones propagated from T3 (after anti-HBe seroconversion) were of genotype Ba, C and/or recombinant within the pre-S region. At T4, all clones were of genotype Ba with a 123 bp (from nt 3147 of the pre-S1 region to nt 54 of the pre-S2 region) in-frame pre-S deletion and had lost the start codon of the middle envelope protein and the nucleocapsid-binding site. Phylogenetic analysis showed that genetic distance was greater at T3 after seroconversion to anti-HBe. By using SimPlot, the breakpoint of one pre-S recombinant was located at nt 3069-3100 and the other two at nt 49-87. In conclusion, HBV genotype Ba may overtake genotype C as the predominant strain after anti-HBe seroconversion in acute hepatitis B. Recombination within the pre-S region emerged transiently and the pre-S deletion mutant was finally cleared.

Recombination in the genesis and evolution of hepatitis B virus genotypes

Hepatitis B virus (HBV) infection is widely distributed in both human and ape populations throughout the world and is a major cause of human morbidity and mortality. HBV variants are currently classified into the human genotypes A to H and species-associated chimpanzee and gibbon/orangutan groups. To examine the role of recombination in the evolution of HBV, large-scale data retrieval and automated phylogenetic analysis (TreeOrder scanning) were carried out on all available published complete genome sequences of HBV. We detected a total of 24 phylogenetically independent potential recombinants (different genotype combinations or distinct breakpoints), eight of which were previously undescribed. Instances of intergenotype recombination were observed in all human and ape HBV variants, including evidence for a novel gibbon/genotype C recombinant among HBV variants from Vietnam. By recording sequence positions in trees generated from sequential fragments across the genome, violations of phylogeny between trees also provided evidence for frequent intragenotype recombination between members of genotypes A, D, F/H, and gibbon variants but not in B, C, or the Asian B/C recombinant group. In many cases, favored positions for both inter- and intragenotype recombination matched positions of phylogenetic reorganization between the human and ape genotypes, such as the end of the surface gene and the core gene, where sequence relationships between genotypes changed in the TreeOrder scan. These findings provide evidence for the occurrence of past, extensive recombination events in the evolutionary history of the currently classified genotypes of HBV and potentially in changes in its global epidemiology and associations with human disease.

A novel recombinant of Hepatitis B virus genotypes G and C isolated from a Thai patient with hepatocellular carcinoma

Genomic recombination between different genotypes of Hepatitis B virus (HBV) resulting in hybrid strains has been increasingly documented. In this study, a novel recombinant of HBV genotypes G and C isolated from a Thai patient with hepatocellular carcinoma is reported. Based on phylogenetic analyses of the S, P and X genes and the entire genome, the HBV isolate clustered on a branch within genotype G, but clustered with genotype C on analysis of the C gene. Using the program simplot and bootscanning analysis, the recombination breakpoints were located at nt 1860 and 2460 of the precore/core region. The hallmarks of the original genotype G, including a 36 bp insertion in the core region and dual stop codons in the precore region, were not identified in this isolate. These data should encourage further investigations on the epidemiological and virological characteristics of HBV genotype G involved in recombination with other genotypes.

Distinct geographic distributions of hepatitis B virus genotypes in patients with acute infection in Japan

Genotypes of hepatitis B virus (HBV) were determined in 145 patients with acute hepatitis B from various districts in Japan to establish their geographic distribution and evaluating the influence on the clinical illness and outcome. Genotypes were A in 27 (19%) patients, B in 8 (5%), C in 109 (75%) and mixed with B and C in the remaining one (1%). Genotype A was more frequent in metropolitan than the other areas (21/69 (30%) vs. 6/76 (8%), P < 0.001). On phylogenetic analysis, seven of the nine (78%) HBV/A isolates selected at random clustered with those from Europe and the United States, while the remaining two with those of subgroup A' prevalent in Asia and Africa. Maximum ALT levels were lower (2069 +/- 1075 vs. 2889 +/- 1867 IU/L, P = 0.03) and baseline HBV DNA titers were higher (5.90 +/- 1.45 vs. 5.13 +/- 1.36 log genome equivalents (LGE)/ml, P = 0.002) in patients infected with genotype A than C. Hepatitis B surface antigen persisted longer in patients infected with genotype A than C (1.95 +/- 1.09 vs. 1.28 +/- 1.42 months, P = 0.02). HBV infection became chronic in one (4%) patient with genotype A and one (1%) with genotype C infection. Fulminant hepatic failure developed in none of the patients with genotype A, one (13%) with genotype B and five (5%) with genotype C. The point mutation in the precore region (A1896) or the double mutations in the basic core promoter (BCP) region (T1762/A1764) were detected in none of the patients with genotype A, two (25%) with genotype B and 27 (26%) with genotype C. In conclusion, genotype A is frequent in patients with acute hepatitis B in metropolitan areas of Japan, probably reflecting particular transmission routes, and associated with longer and milder clinical course than genotype C.

Variability and conservation in hepatitis B virus core protein

Background

Hepatitis B core protein (HBVc) has been extensively studied from both a structural and immunological point of view, but the evolutionary forces driving sequence variation within core are incompletely understood.

Results

In this study, the observed variation in HBVc protein sequence has been examined in a collection of a large number of HBVc protein sequences from public sequence repositories. An alignment of several hundred sequences was carried out, and used to analyse the distribution of polymorphisms along the HBVc. Polymorphisms were found at 44 out of 185 amino acid positions analysed and were clustered predominantly in those parts of HBVc forming the outer surface and spike on intact capsid. The relationship between HBVc diversity and HBV genotype was examined. The position of variable amino acids along the sequence was examined in terms of the structural constraints of capsid and envelope assembly, and also in terms of immunological recognition by T and B cells.

Conclusion

Over three quarters of amino acids within the HBVc sequence are non-polymorphic, and variation is focused to a few amino acids. Phylogenetic analysis suggests that core protein specific forces constrain its diversity within the context of overall HBV genome evolution. As a consequence, core protein is not a reliable predictor of virus genotype. The structural requirements of capsid assembly are likely to play a major role in limiting diversity. The phylogenetic analysis further suggests that immunological selection does not play a major role in driving HBVc diversity.

Co-Infection with Hepatitis B Virus Genotype D and Other Genotypes in Western Japan

OBJECTIVE

Genotypes B and C are the prevalent hepatitis B virus (HBV) genotypes in eastern Asia. Although very rare in this region of the world, genotype D was found to be prevalent in a small area of western Japan. In this study, we confirm the frequency and clinical significance of co-infection with different genotypes among patients from that area infected with genotype D.

METHODS

Twenty-three patients from the same area of western Japan infected with HBV genotype D, determined using a genotyping enzyme immunoassay, were studied. Cloning was done using DNA extracted from serum samples, and polymerase chain reaction assays with the restriction fragment length polymorphism for HBV genotyping were performed with 10 clones from each patient.

RESULTS

Four (17.4%) of the 23 patients were found to be co-infected with HBV genotype C, and the HB surface antigen subtype was ayw in both mono- and co-infected patients. No clinical differences were found between mono-infected and co-infected patients carrying genotype D.

CONCLUSION

A significant number of patients from the study area found to be infected with HBV genotype D were co-infected with genotype C. Additional study with a larger number of patients is needed to elucidate the possible clinical significance.