Genetic diversity of hepatitis B virus as an important factor associated with differences in clinical outcomes

Hepatitis B virus genome diversity in adolescents: Tenofovir disoproxil fumarate treatment effect and HBeAg serocon version

More systematic analysis of hepatitis B virus (HBV) genome diversity, linked with tenofovir disoproxil fumarate (TDF) treatment and HBeAg seroconversion, are needed. GS-US-174-0115 was a double-blind, placebo-controlled, Phase 3, 192-week clinical trial that evaluated TDF in adolescents with chronic hepatitis B (CHB). HBV full-genome deep sequencing was performed using Illumina MiSeq at baseline (BL; n = 85), Week 8 (W8; n = 80), Week 72 (W72; PBO only, n = 42), and treatment-free follow-up (TDF only, n = 25). The viral diversity was calculated using Shannon entropy and population nucleotide diversity with a 2% variant cutoff. Our data showed (i) a higher viral diversity in the X region at baseline than the core/polymerase/surface regions, (ii) higher core/surface viral diversity at baseline for patients with seroconversion, (iii) an expected reduction in viral diversity after 8 weeks of TDF treatment, and (iv) a drop in viral diversity at W72 for patients receiving placebo with a seroconversion (n = 7). The higher viral diversity in X was associated with higher baseline alanine aminotransferase (ALT) levels (p < .001). Patients with greater reduction of diversity at W8 of TDF treatment had higher baseline ALT levels. For placebo patients who seroconverted, the drop in viral diversity at W72 (p = .04) coincided with reduction of serum HBV DNA (average change from baseline = -4.10 log10 copies/ml) and unique combinations of variants were enriched in a patient's viral population post seroconversion. The basal core promoter (BCP) variants, A1762T and G1764A, and the pC variant, G1896A, were most often enriched at or after seroconversion.

Transmission of SARS-CoV-2 in domestic cats imposes a narrow bottleneck

The evolutionary mechanisms by which SARS-CoV-2 viruses adapt to mammalian hosts and, potentially, undergo antigenic evolution depend on the ways genetic variation is generated and selected within and between individual hosts. Using domestic cats as a model, we show that SARS-CoV-2 consensus sequences remain largely unchanged over time within hosts, while dynamic sub-consensus diversity reveals processes of genetic drift and weak purifying selection. We further identify a notable variant at amino acid position 655 in Spike (H655Y), which was previously shown to confer escape from human monoclonal antibodies. This variant arises rapidly and persists at intermediate frequencies in index cats. It also becomes fixed following transmission in two of three pairs. These dynamics suggest this site may be under positive selection in this system and illustrate how a variant can quickly arise and become fixed in parallel across multiple transmission pairs. Transmission of SARS-CoV-2 in cats involved a narrow bottleneck, with new infections founded by fewer than ten viruses. In RNA virus evolution, stochastic processes like narrow transmission bottlenecks and genetic drift typically act to constrain the overall pace of adaptive evolution. Our data suggest that here, positive selection in index cats followed by a narrow transmission bottleneck may have instead accelerated the fixation of S H655Y, a potentially beneficial SARS-CoV-2 variant. Overall, our study suggests species- and context-specific adaptations are likely to continue to emerge. This underscores the importance of continued genomic surveillance for new SARS-CoV-2 variants as well as heightened scrutiny for signatures of SARS-CoV-2 positive selection in humans and mammalian model systems.

Transmission of SARS-CoV-2 in domestic cats imposes a narrow bottleneck

The evolutionary mechanisms by which SARS-CoV-2 viruses adapt to mammalian hosts and, potentially, undergo antigenic evolution depend on the ways genetic variation is generated and selected within and between individual hosts. Using domestic cats as a model, we show that SARS-CoV-2 consensus sequences remain largely unchanged over time within hosts, while dynamic sub-consensus diversity reveals processes of genetic drift and weak purifying selection. We further identify a notable variant at amino acid position 655 in Spike (H655Y), which was previously shown to confer escape from human monoclonal antibodies. This variant arises rapidly and persists at intermediate frequencies in index cats. It also becomes fixed following transmission in two of three pairs. These dynamics suggest this site may be under positive selection in this system and illustrate how a variant can quickly arise and become fixed in parallel across multiple transmission pairs. Transmission of SARS-CoV-2 in cats involved a narrow bottleneck, with new infections founded by fewer than ten viruses. In RNA virus evolution, stochastic processes like narrow transmission bottlenecks and genetic drift typically act to constrain the overall pace of adaptive evolution. Our data suggest that here, positive selection in index cats followed by a narrow transmission bottleneck may have instead accelerated the fixation of S H655Y, a potentially beneficial SARS-CoV-2 variant. Overall, our study suggests species- and context-specific adaptations are likely to continue to emerge. This underscores the importance of continued genomic surveillance for new SARS-CoV-2 variants as well as heightened scrutiny for signatures of SARS-CoV-2 positive selection in humans and mammalian model systems.

Application of Next-Generation Sequencing to Reveal How Evolutionary Dynamics of Viral Population Shape Dengue Epidemiology

Dengue viral (DENV) infection results in a wide spectrum of clinical manifestations from asymptomatic, mild fever to severe hemorrhage diseases upon infection. Severe dengue is the leading cause of pediatric deaths and/or hospitalizations, which are a major public health burden in dengue-endemic or hyperendemic countries. Like other RNA viruses, DENV continues to evolve. Adaptive mutations are obscured by the major consensus sequence (so-called wild-type sequences) and can only be identified once they become the dominant viruses in the virus population, a process that can take months or years. Traditional surveillance systems still rely on Sanger consensus sequencing. However, with the recent advancement of high-throughput next-generation sequencing (NGS) technologies, the genome-wide investigation of virus population within-host and between-hosts becomes achievable. Thus, viral population sequencing by NGS can increase our understanding of the changing epidemiology and evolution of viral genomics at the molecular level. This review focuses on the studies within the recent decade utilizing NGS in different experimental and epidemiological settings to understand how the adaptive evolution of dengue variants shapes the dengue epidemic and disease severity through its transmission. We propose three types of studies that can be pursued in the future to enhance our surveillance for epidemic prediction and better medical management.

An Association Between Core Mutations in Hepatitis B Virus Genotype F1b and Hepatocellular Carcinoma in Alaskan Native People

Hepatitis B virus (HBV) genotype F1b infection is strongly associated with hepatocellular carcinoma (HCC) in young Alaskan Native (AN) people. However, the mechanisms by which genotype F1b causes HCC are unclear. Here, we analyzed the clinical and virological significance of genotype F1b in long-term serial samples from 20 HCC patients with HBV infection. Complete sequence analyses revealed that all isolates were genotype F1b. In the HCC patients, T1938C and A2051C mutations in the core region had accumulated significantly with A1762T/G1764A mutations in the basal core promoter (BCP) region and G1896A mutation in the precore (PC) region. Several HBV clones containing the core mutations were examined for their replication efficiency and core stability in vitro. Clones containing the A2051C mutation replicated more efficiently than the wild type in association with enhanced stability of core protein dimerization. In chimeric mice with human hepatocytes carrying BCP/PC/2051 mutant but not with wild-type virus, liver fibrosis was induced in association with high levels of serum HBV DNA and hepatitis B surface antigen. Interestingly, microarray analysis and validation study showed that five genes associated with cell proliferation or carcinogenesis, v-myc avian myelocytomatosis viral oncogene homolog, Grb2-associated binding protein 2, bradykinin receptor B2, follistatin, and mitogen-activated protein kinase kinase kinase 8, were significantly up-regulated in human hepatocytes infected with genotype F1b, particularly the BCP/PC/2051 mutant, compared with other genotypes. Conclusion: We have identified an association between Alaska-specific core mutations and HCC development in AN people infected with genotype F1b; accumulation of these core mutations during the course of chronic infection with genotype F1b would contribute to HCC development in AN people earlier in life.

Widespread geographical disparities in chronic hepatitis B virus infection in Algeria

Algeria is the largest country of Africa, with a population of 40 million inhabitants living in disparate environments from the Sahara to the large cities of the Mediterranean coast. The molecular epidemiology of hepatitis B virus (HBV) variants has been partially described, but variations in the seroprevalence of HBV surface antigen (HBsAg) throughout the Algerian territories are still poorly described. We analyzed demographic features of new cases of chronic infection collected in 41 administrative regions (covering 92% of the population) in 2013. The mean age of the 1876 HBsAg(+) patients was 36.8 ± 14.2 years, with a slight excess of males (54%). The seroprevalence of HBV early antigen (HBeAg) was 9.3%, and the mean virus load was 3.2 ± 1.8 log IU/ml. A subset of 15.2% of patients was already cirrhotic at disease discovery. An important heterogeneity was observed throughout the country, with nine regions displaying a significant excess of cases. These regions formed four distinct foci located in distant parts of the country: Adrar-Bechar (southwest), El-Oued-Tebessa (east), M'Sila-Sétif (north central) and Oran-Aïn Temouchent (northwest). An excess of cases was found as well in the national capital Algiers. Patients from southern regions with an excess of cases (Bechar, Adrar, El Oued) were significantly younger (32.0 ± 10.7 years), as were patients from the regions of Bejaia and Bouira (32.1 ± 10.6). The southwestern regions were also marked by a significant imbalance of the sex ratio (58 vs 39% of female cases, P = 4.5 E-5). The highest HBeAg seroprevalence was observed in Setif (26.4 vs. 7.6%, OR = 4.3, 95% CI 2.6-6.5, P = 1.1 × 10^-11) in accordance with the higher virus loads observed in the patients (3.9 ± 2.3 vs. 3.1 ± 1.6, P = 0.0002). In conclusion, we observed heterogeneity in HBsAg seroprevalence, demographic traits, and disease evolution in Algeria. Further studies are now warranted to shed light on these differences, which are presumably due to variability in transmission routes or in the infectivity of viral isolates.

Distribution of hepatitis B virus genotype and cancer predicting precore and basal core promoter mutations

BACKGROUND

Chronic hepatitis B (CHB) infection which is associated with an increased risk of developing liver disease including cirrhosis and hepatocellular carcinoma. Viral factors that may increase the risk for HCC development include HBV DNA level, genotypes, and naturally occurring mutations such as hepatitis B virus precore (PC) (G1896A) and basal core promoter (BCP) A1762T/G1764A double mutations. HBV genotypes and subgenotypes can significantly influence HBeAg seroconversion rates, viremia levels, mutational patterns that could significantly influence the heterogeneity in clinical manifestations and even response to antiviral therapy.

METHOD

94 CHB infected individuals with detectable serum HBV DNA levels were studied. HBsAg, HBeAg, anti-HBc IgM antibody estimations were done by ELISA. HBV DNA estimation was done. The HBV genotypes were determined by TSP-PCR and 10 samples randomly selected for DNA sequencing. PC and BCP mutations were determined by DNA sequence analysis of core region.

RESULT

Of 94 study participant samples with detectable serum HBV DNA levels, 75 were successfully genotyped and sequenced for BCP/PC region. 30/75 (40%) harbored PC and BCP mutations. The total Double mutations of BCP at A1762T/G1764A nucleotide positions, and PC mutation at G1896A nucleotide position were seen in 29.3% and 21.3%, respectively. All 75 isolates were subtype D using TSP-PCR. However, by sequencing 2/10 were subtype A, while 8 were subtype D.

CONCLUSION

Our study reinforces that D is the predominant genotype in Indian population. It reveals that Indian CHB subjects have increased prevalence of BCP & PC mutations, which possibly may lead to development of HCC.

Immune-driven adaptation of hepatitis B virus genotype D involves preferential alteration in B-cell epitopes and replicative attenuation--an insight from human immunodeficiency virus/hepatitis B virus coinfection

An important driving force behind the sequence diversity of hepatitis B virus (HBV) is viral adaptation to host immune responses. To gain an insight into the impact of host immunity on genetic diversification and properties of HBV, we characterized HBV of genotype D from treatment-naive hepatitis B e antigen-positive (EP) and hepatitis B e antigen-negative (EN) patients with chronic hepatitis B (CHB), where HBV is under stronger immune pressure, with that of HBV derived from human immunodeficiency virus (HIV)/HBV-coinfected individuals, where HIV infection has significantly weakened the immune system. Full-length sequence analysis showed that HBV heterogeneity was most extensive in EN-CHB followed by EP-CHB and HIV/HBV coinfection. The relative magnitude of non-synonymous changes within B-cell epitopes was greater than that in T-cell epitopes of HBV open reading frames (ORFs) in both EP-CHB and EN-CHB. Nine amino acid substitutions were identified in B-cell epitopes and one in a T-cell epitope of HBV in EN-CHB, most of which resulted in altered hydrophobicities, as determined using the Kyte and Doolittle method, relative to wild-type residues found in HBV from the HIV-positive group. Additionally, 19 substitutions occurred at significantly higher frequencies in non-epitope regions of HBV ORF-P in EN-CHB than HIV/HBV-coinfected patients. In vitro replication assay demonstrated that the substitutions, particularly in reverse transcriptase and RNaseH domains of ORF-P, resulted in a decline in replication capacity of HBV. Hence, our results indicate that HBV adapts to increasing immune pressure through preferential mutations in B-cell epitopes and by replicative attenuation. The viral epitopes linked to immune response identified in this study bear important implications for future HBV vaccine studies.

HBV endemicity in Mexico is associated with HBV genotypes H and G

Hepatitis B virus (HBV) genotypes have distinct genetic and geographic diversity and may be associated with specific clinical characteristics, progression, severity of disease and antiviral response. Herein, we provide an updated overview of the endemicity of HBV genotypes H and G in Mexico. HBV genotype H is predominant among the Mexican population, but not in Central America. Its geographic distribution is related to a typical endemicity among the Mexicans which is characterized by a low hepatitis B surface antigen seroprevalence, apparently due to a rapid resolution of the infection, low viral loads and a high prevalence of occult B infection. During chronic infections, genotype H is detected in mixtures with other HBV genotypes and associated with other co-morbidities, such as obesity, alcoholism and co-infection with hepatitis C virus or human immunodeficiency virus. Hepatocellular carcinoma prevalence is low. Thus, antiviral therapy may differ significantly from the standard guidelines established worldwide. The high prevalence of HBV genotype G in the Americas, especially among the Mexican population, raises new questions regarding its geographic origin that will require further investigation.

Molecular biology of the hepatitis B virus for clinicians

Hepatitis B virus (HBV) infection is one of the major global health problems, especially in economically under-developed or developing countries. HBV infection can lead to a number of clinical outcomes including chronic infection, cirrhosis and liver cancer. It ranks among the top 10 causes of death, being responsible for around 1 million deaths every year. Despite the availability of a highly efficient vaccine and potent antiviral agents, HBV infection still remains a significant clinical problem, particularly in those high endemicity areas where vaccination of large populations has not been possible due to economic reasons. Although HBV is among the smallest viruses in terms of virion and genome size, it has numerous unique features that make it completely distinct from other DNA viruses. It has a partially double stranded DNA with highly complex genome organization, life cycle and natural history. Remarkably distinct from other DNA viruses, it uses an RNA intermediate called pregenomic RNA (pgRNA) and reverse transcriptase for its genome replication. Genome replication is accomplished by a complex mechanism of primer shifting facilitated by direct repeat sequences encoded in the genome. Further, the genome has evolved in such a manner that every single nucleotide of the genome is used for either coding viral proteins or used as regulatory regions or both. Moreover, it utilizes internal in-frame translation initiation codons, as well as different reading frames from the same RNA to generate different proteins with diverse functions. HBV also shows considerable genetic variability which has been related with clinical outcomes, replication potential, therapeutic response etc. This review aims at reviewing fundamental events of the viral life cycle including viral replication, transcription and translation, from the molecular standpoint, as well as, highlights the clinical relevance of genetic variability of HBV.

Molecular characterization of hepatitis B virus X gene in chronic hepatitis B patients

Background

HBV-X protein is associated with the pathogenesis of HBV related diseases, specially in hepatocellular carcinomas of chronic patients. Genetic variability of the X gene includes genotypic specific variations and mutations emerging during chronic infection. Its coding sequence overlaps important regions for virus replication, including the basal core promoter. Differences in the X gene may have implications in biological functions of the protein and thus, affect the evolution of the disease. There are controversial results about the consequences of mutations in this region and their relationship with pathogenesis. The purpose of this work was to describe the diversity of HBV-X gene in chronic hepatitis patients infected with different genotypes, according to liver disease.

Methods

HBV-X gene was sequenced from chronic hepatitis B patient samples, analyzed by phylogeny and genotyped. Nucleotide and aminoacid diversity was determined calculating intragenetic distances. Mutations at 127, 130 and 131 aminoacids were considered in relation to liver disease.

Results

The most prevalent genotype detected in this cohort was F (F1 and F4), followed by D and A. Most of the samples corresponding to genotypes A and F1 were HBeAg(+) and for genotypes D and F4, HBeAg(−) samples were represented in a higher percentage. Intragenetic distance values were higher in HBeAg(−) than in positive samples for all genotypes, and lower in overlapped regions, compared to single codification ones. Nucleotide and aminoacid diversities were higher in HBeAg(−), than in HBeAg(+) samples.

Conclusions

Independently of the infecting genotypes, mutations at any of 127, 130 and/or 131 aminoacid positions and HBeAg(−) status were associated with mild liver disease in this cohort.

Variations in the functional domain of basal core promoter of hepatitis B virus among Eastern Indian patients with prevalence of genotypes A, C, and D among the same ethnic population

Mutations in the basal core promoter (BCP) and precore (PC) regions are associated with persistent and intermittently high hepatitis B virus (HBV) replication in several patients. The variability in the functional domains of BCP and PC region of HBV and their association with disease progression and clinical outcome were assessed in Eastern India, an unique region where three HBV genotypes, A, D, and C are prevalent among the same ethnic group. PCR amplification and direct sequencing of BCP and PC region was done on sera obtained from 130 HBsAg positive subjects with different clinical presentations. Associations of the apparent risk factors with clinical advancement were evaluated by statistical methods including multiple logistic regression analyses (MLR). HBV genotype A was present in 33.08%, C in 25.38%, and D in 41.54% cases. Genotypes A and C were associated with higher rate of T1762/A1764 mutations than the most predominant genotype D. HBeAg negative state was associated with considerably higher rate of C1753 mutation. T1762/A1764 along with C1753 was common among cirrhosis and T1762/A1764 without C1753 was frequent among chronic liver disease cases. No significant association was found between A1896 point mutation and clinical status. Multivariate analysis revealed that T1762/A1764 double mutation, HBV/A, age ≥25 years, C1753 and A1899 were critical factors for clinical advancement while age ≥25 years and C1753 as significant predictor for cirrhosis in comparison with chronic liver disease. In conclusion, the analysis of the BCP variability may help in monitoring the progression towards advanced liver disease in Eastern Indian patients.

A genetic variant of hepatitis B virus divergent from known human and ape genotypes isolated from a Japanese patient and provisionally assigned to new genotype J

Hepatitis B virus (HBV) of a novel genotype (J) was recovered from an 88-year-old Japanese patient with hepatocellular carcinoma who had a history of residing in Borneo during the World War II. It was divergent from eight human (A to H) and four ape (chimpanzee, gorilla, gibbon, and orangutan) HBV genotypes, as well as from a recently proposed ninth human genotype I, by 9.9 to 16.5% of the entire genomic sequence and did not have evidence of recombination with any of the nine human genotypes and four nonhuman genotypes. Based on a comparison of the entire nucleotide sequence against 1,440 HBV isolates reported, HBV/J was nearest to the gibbon and orangutan genotypes (mean divergences of 10.9 and 10.7%, respectively). Based on a comparison of four open reading frames, HBV/J was closer to gibbon/orangutan genotypes than to human genotypes in the P and large S genes and closest to Australian aboriginal strains (HBV/C4) and orangutan-derived strains in the S gene, whereas it was closer to human than ape genotypes in the C gene. HBV/J shared a deletion of 33 nucleotides at the start of preS1 region with C4 and gibbon genotypes, had an S-gene sequence similar to that of C4, and expressed the ayw subtype. Efficient infection, replication, and antigen expression by HBV/J were experimentally established in two chimeric mice with the liver repopulated for human hepatocytes. The HBV DNA sequence recovered from infected mice was identical to that in the inoculum. Since HBV/J is positioned phylogenetically in between human and ape genotypes, it may help to trace the origin of HBV and merits further epidemiological surveys.

Hepatitis B virus genotype G epidemiology and co-infection with genotype A in Canada

Hepatitis B virus (HBV) genotype G (HBV/G) is an unusual variant, and little is known about its epidemiology and natural history, particularly the requirement for a co-infecting HBV genotype and their relationship during infection. This study investigated the quasispecies nature of co-infecting genotypes in 39 samples collected over a 6 year period from 13 HBV/G-infected patients. HBV/G infections were found to occur predominantly in males (92 %) and were primarily associated with male homosexual sex (67 %). All patients were infected with HBV/G and HBV/A, or a recombinant HBV/A/G strain. Co-infecting genotypic prevalence was often observed to fluctuate over time, with periods of HBV/G monoinfection in some patients. The average sequence divergence among Canadian HBV/G strains was 1.57+/-0.62 %. Thus, all HBV/G infections in Canada occur in the context of co-infection or recombination with HBV/A, and strains display increased sequence divergence compared with all known HBV/G sequences described to date.

Genotype D amongst injection drug users with acute hepatitis B virus infection in British Columbia

The eight genotypes of hepatitis B virus (HBV) exhibit distinct geographical distributions. This study identified HBV genotypes and transmission modes associated with acute infection in British Columbia (BC), Canada, from 2001 to 2005. Seventy cases of acute HBV in BC were identified from laboratory reports using a standardized case definition. Interviews for risk factors and hepatitis history were conducted for each case. HBV genotypes were determined by BLAST comparison analysis of the surface (S) or preS gene sequence. To illustrate the distribution of genotypes identified amongst acute cases in BC, an annotated map was produced showing the global occurrence of HBV genotypes. The majority of acute HBV cases occurred in Caucasian, Canadian-born males, with 30% of cases reporting injection drug use (IDU) and 21% reporting incarceration. The most common genotype observed was genotype D (62.9%), followed by genotypes A (18.6%), C (11.4%), B (4.3%), and E (1.4%). A significant association was observed between Genotype D and IDU (P = 0.0025) and previous incarceration (P = 0.0067). Phylogenetic analysis of the S gene sequence demonstrated identical or high genetic relatedness amongst genotype D viral strains (86% sub-genotype D3), thus verifying transmission clustering amongst BC injection drug users. The association between acute HBV genotype and reported transmission modes has not been previously described in North America. Tracking of genotypes can help identify disease transmission patterns and target at-risk populations for preventive immunization.

A low steady HBsAg seroprevalence is associated with a low incidence of HBV-related liver cirrhosis and hepatocellular carcinoma in Mexico: a systematic review

To address the relationship between hepatitis B virus (HBV) endemicity and HBV-related liver diseases in Mexico. Research literature reporting on HBsAg and antibody to hepatitis B core antigen (anti-HBc) prevalence in Mexican study groups were searched in NLM Gateway, PubMed, IMBIOMED, and others. Weighted mean prevalence (WMP) was calculated from the results of each study group. A total of 50 studies were analyzed. Three nationwide surveys revealed an HBsAg seroprevalence of less than 0.3%. Horizontal transmission of HBV infection occurred mainly by sexual activity and exposure to both contaminated surgical equipment and body fluids. High-risk groups exposed to these factors included healthcare workers, pregnant women, female sex workers, hemodialysis patients, and emergency department attendees with an HBsAg WMP ranging from 1.05% (95% confidence interval [CI], 0.68-1.43) to 14.3% (95% CI, 9.5-19.1). A higher prevalence of anti-HBc in adults than those younger than 20 years was associated with the main risk factors. Anti-HBc WMP ranged from 3.13% (95% CI, 3.01-3.24) in blood donors to 27.7% (95% CI, 21.6-33.9) in hemodialysis patients. A heterogeneous distribution of HBV infection was detected, mainly in native Mexican groups with a high anti-HBc WMP of 42.0% (95% CI, 39.5-44.3) but with a low HBsAg WMP of 2.9% (95% CI 2.08-3.75). Estimations of the Mexican population growth rate and main risk factors suggest that HBsAg seroprevalence has remained steady since 1974. A low HBsAg prevalence is related to the low incidence of HBV-related liver cirrhosis and hepatocellular carcinoma (HCC) previously reported in Mexico.

An overview of molecular epidemiology of hepatitis B virus (HBV) in India

Hepatitis B virus (HBV) is one of the major global public health problems. In India, HBsAg prevalence among general population ranges from 2% to 8%, placing India in intermediate HBV endemicity zone and the number of HBV carriers is estimated to be 50 million, forming the second largest global pool of chronic HBV infections. India is a vast country, comprised of multiracial communities with wide variations in ethnicity and cultural patterns, which is attributable to its geographical location, gene influx due to invasion and/or anthropological migrations in the past. Moreover, recent increase in trade, trafficking and use of illicit drugs has also considerably influenced the epidemiology of HBV, specifically in the eastern and north eastern parts of India. However, data on the molecular epidemiology of HBV in India is scanty. HBV genotypes A and D have been well documented from different parts of mainland India. Interestingly, in addition to genotypes A and D, genotype C having high nucleotide similarity with south East Asian subgenotype Cs/C1 strain, have been detected exclusively from eastern Indian HBV carriers, suggesting a recent introduction. Thus, compared to other parts of India, the molecular epidemiology of HBV is naturally distinct in eastern India. Very recently, taking the advantage of circulation of three distinct HBV genotypes within the population of eastern India, different aspects of HBV molecular epidemiology was studied that revealed very interesting results. In this study, the clinical significance of HBV genotypes, core promoter and precore mutations, possible routes of introduction of HBV genotype C in eastern India, the clinical implications of x gene variability, prevalence of the AFB₁ induced p53 gene codon 249 mutation, the transmission potentiality of HBV among asymptomatic/inactive or occult HBV carriers and the genetic variability of HBV persisting in the PBL was investigated. In this manuscript, the information available on the molecular epidemiology of HBV in India has been reviewed and the results of studies among the eastern Indian population have been summarised.

Transmission of hepatitis B virus (HBV) genotypes among Japanese immigrants and natives in Bolivia

Hepatitis B virus genotypes are associated with transmission pattern, virological and clinical features and outcome of the chronic infection course. HBV genotypes other than Genotype F (HBV/F) are considered a reflection of human migration into South America. A total of 487 individuals in Bolivia, including Japanese immigrants (n=287) and natives (n=200), were screened for HBV serological markers. Overall 22/487 (4.5%) of the subjects were positive for HBsAg, 217/487 (44.5%) for anti-HBc and 162/487 (33.3%) for anti-HBs. Genotypes were determinable in 22 cases by EIA, followed by sequencing and phylogenetic analysis in 17 cases. HBV genotype distribution in Japanese and Bolivians was HBV/F (4 and 8); HBV/C (5 and 3); and HBV/B (1 and 1), respectively. Phylogenetic analyses of nine complete and eight partial (HBsAg/pre-core/core region) genomes, revealed that HBV/F strains cluster with previously reported regional strains, whereas HBV/B and HBV/C strains belonged to Asian subgenotype B2 (Ba) and C2 (Ce), respectively. Japanese immigrants might have introduced HBV/B and HBV/C to natives in Bolivia, conversely, exposed to the indigenous HBV/F. This report provides evidence of an inter-communities transmission of HBV revealed by its genotypes. Further study is required to investigate peculiarities of the genotypes in different ethnic groups in Bolivia.

Dengue virus evolution and virulence models

Dengue virus transmission has increased dramatically in the past 2 decades, making this virus one of the most important mosquito-borne human pathogens. The emergence of dengue hemorrhagic fever in most tropical countries has made its control a public health priority, but no vaccines or treatments exist. Little is understood about dengue virus pathogenesis, because no other animals develop symptoms of disease, and research, therefore, has been limited to studies involving patients. Although epidemiologic and evolutionary studies have pointed to host and viral factors in determining disease outcome, only recently developed models could prove the importance of viral genotypes in causing severe epidemics. The influence of host immune status and mosquito vectorial capacity are also being tested in mathematical models to determine virus population dynamics. Therefore, new technologies are allowing us to better understand how specific virus variants cause more disease than others, and these virus variants should be targeted for detection, control, and treatment.