Genetic variability in hepatitis B viruses

Epidemiology of HBV genotypes by nested PCR with multi-paired primers

AIM: To investigate the epidemiology of HBV genotypes among HBV-infected persons in northern China.

METHODS: The HBV DNA in 801 sera samples collected from hepatitis patients (594), healthy controls (154), and HCV-infected patients (53) were tested by nested PCR, the positive sera were then genotyped by nested PCR with six pairs of HBV genotype-specific primers (A to F).

RESULTS: 464 samples (57.9%) were HBV DNA positive among the 801 samples. Among 594 cases with various hepatitis B clinical manifestations, 74.4% (442/594) were HBV-DNA positive, while 8.4% (13/154) of healthy controls were HBV-DNA positive. There was significant difference between the hepatitis patients and healthy controls (P < 0.01). 17% (9/53) of HCV-infected patients were HBV-DNA positive, too. Among the 464 HBV-DNA positive samples, the persentage of genotype A was 5.2% (24/464), genotype B 7.1% (33/464), and type C 77.2% (358/464), type D 2.4% (11/464), while none of type E and F had been found in those samples. 14 samples (3%) were both type B and C positive. The 24 samples could not be genotyped in this study.

CONCLUSION: The HBV genotypes prevailed among HBV-infected persons in northern China are types A, B, C, and D, and the major genotype is type C (77.2%). Type C is also the major genotype among the clinical groups. There is no statistical difference between the groups.

Clinical significance of hepatitis B virus genotypes, variants, and mutants

Emerging evidence suggests that hepatitis B virus (HBV) genotypes may influence the rate of spontaneous and interferon-induced hepatitis B e antigen (HBeAg) seroconversion as well as the natural history of liver disease. In contrast, the dinical significance of precore and core promoter variants associated with HBeAg negative liver disease is less certain in light of the many competing host and virologic factors noted in reported studies. HBV surface mutants are primarily associated with prior vaccine or hepatitis B immune globulin exposure and do not appear to have untoward virulence or association with occult HBV infection. Polymerase mutants with reduced drug sensitivity and phenotypic resistance are commonly detected in patients receiving prolonged antiviral therapy and have a variable impact on disease outcomes. The introduction of additional nucleoside/nucleotide analog agents will likely lead to the development of further unique polymerase mutants with varying pathogenicity and cross-resistance to existing drugs.

Critical overview and outlook: pathogenesis, prevention, and treatment of hepatitis and hepatocarcinoma caused by hepatitis B virus

Viral hepatitis B is an enigmatic disease in which the host's own immune response to persistent viral infection may bring about host destruction through antiviral inflammatory responses which might otherwise present as a benign or inapparent disease. The simple solution to the hepatitis B problem is by immunoprophylaxis using the vaccine licensed in 1981, which prevents both infection and the late sequelae of liver cirrhosis and hepatocarcinoma. Immunotherapeutic vaccines against persistent hepatitis B infection have not been successful and new explorations are being directed to therapies which include antisense, ribozymes, gene silencing by RNA interference (RNAi) and aptamer approaches. Limited benefits from nucleoside therapy and limitations in opportunity for liver transplantation have left a large void of curative treatments. Findings with respect to e antigen tolerance provide a basis for exploration to determine whether passively administered e antigen might suppress cell-mediated immunity, creating a commensal state in which virus persists but without pathologic damage to the host. Therapy of hepatocarcinoma by conventional chemotherapy, radiation, or surgical resection and ablation gives little hope for restoration of health unless the tumor is detected very early. The large engagement of the world medical science community to develop therapeutic vaccines against cancer is now in major clinical trials to determine the hope and credibility for the immunization approach. Vaccines based on tumor peptides which are linked to heat shock proteins and directed to host dendritic cells give reason for excitement and may be the "best show in town". A new era of tumor therapy will need to be based on new discoveries in immune function which are required to pursue immunotherapy on a more rational basis. The many facets of current hepatitis B virology, pathogenesis, immunoprophylaxis, immunotherapeusis, chemotherapy, and tumor pathogenesis and therapy are discussed here, in depth, but in keeping with needed brevity.

Molecular epidemiology of hepatitis B and C virus infections in Asia

The present paper provides a review of the current literature regarding the molecular-based epidemiology of hepatitis B virus (HBV) and hepatitis C virus (HCV), which are very important viruses underlying the etiology of blood-borne infectious diseases worldwide. Particularly, both HBV and HCV are widespread on the Asian continent and are associated with acute and chronic liver diseases, including hepatocellular carcinoma. HBV has been classified into genotypes A through G and shown to have a distinct geographic distribution. In Asia, genotypes B and C of HBV prevail, and genotype C has been shown to cause more serious liver disease than genotype B. High prevalence of HBV mutants with various forms, such as the pre-S mutant, basal core promoter mutant, YMDD motif mutant and vaccine escape mutant, were seen in Asia and these were found to be related to the severity of liver disease and sensitivity to therapy. HCV has also been classified into multiple genotypes and associated with geographic distribution. HCV genotype 1 is less sensitive to interferon therapy and may be associated with the presence of more serious liver disease than the other genotypes. Data on the relation among the HBV/HCV genotypes, their pathogenicity in chronic liver diseases including hepatocellular carcinoma and their effect on therapy are awaited with great interest, especially in Asia, which is an endemic region of blood-borne hepatitis viruses.

Genotype C of hepatitis B virus can be classified into at least two subgroups

A genomic characterization of hepatitis B virus (HBV) was done for 56 pre-S1/pre-S2 genes and 10 full-length HBV genotype C isolates from five Asian countries. Phylogenetic analysis of the pre-S1/pre-S2 genes revealed two major groups within genotype C: one for isolates from southeast Asia including Vietnam, Myanmar and Thailand (named HBV/C1) and the other for isolates from Far East Asia including Japan, Korea and China (named HBV/C2). This finding was confirmed by phylogenetic analysis based on the full-length sequence of 32 HBV genotype C isolates, including 22 from database entries. Two isolates from Okinawa, the island off the southern end of Japan, formed a different branch. Specific amino acid sequence changes were identified in the large S protein (amino acids 51, 54, 60, 62 and 73) and P protein (amino acids 231, 233, 236, 248, 252 and 304). Our results indicate that genotype C of HBV can be classified into at least two subgroups.

A multiplex-PCR to identify hepatitis B virus--enotypes A-F

Eight genotypes (A-H) of hepatitis B virus (HBV) are known with variations in nucleotide sequences greater than 8%. Several recent publications found that the clinical course and outcome of antiviral therapy depended on the genotype of the infecting HBV strain. Large epidemiological studies will require the availability of a system which is rapid, reliable and can be performed on a large number of samples. We have developed a multiplex-PCR assay which uses genotype-specific primer pairs for HBV genotypes A-F. These primer pairs specifically amplified HBV DNA of the respective genotype, either in single or in multiplex-PCR. Sensitivity of the assay was in the range of 10(4) genome equivalents.

A treatment algorithm for the management of chronic hepatitis B virus infection in the United States

BACKGROUND AND AIMS

Chronic hepatitis B is an important public health problem worldwide and in the United States. A treatment algorithm for chronic hepatitis B virus (HBV) infection was developed by a panel of US hepatologists based on new developments in the understanding of the virology of HBV, availability of more sensitive molecular diagnostic testing, and advantages and disadvantages of currently approved therapies.

METHODS

This algorithm is based on available evidence, but where data are lacking, the panel relied on clinical experience and consensus expert opinion.

RESULTS

Serum HBV DNA can be detected at levels as low as 100-1000 copies/mL by using molecular assays and should be determined to establish a baseline level before treatment, monitor response to antiviral therapy, and survey for the development of drug resistance. The primary aim of antiviral therapy is durable suppression of serum HBV DNA to the lowest level possible. The threshold level of HBV DNA for determination of candidacy for therapy is >/=10(5) copies/mL for patients with hepatitis B e antigen (HBeAg)-positive chronic hepatitis B. A lower serum HBV DNA threshold is appropriate for patients with HBeAg-negative chronic hepatitis B and those with decompensated cirrhosis, and the panel recommends thresholds of 10(4) copies/mL and 10(3) copies/mL, respectively.

CONCLUSIONS

Interferon alfa-2b, lamivudine, and adefovir dipivoxil are all approved as initial therapy for chronic hepatitis B and have certain advantages and disadvantages. Issues for consideration include efficacy, safety, incidence of resistance, method of administration, and cost. Studies are under way to explore the safety and efficacy of combination therapy, which may prove to be more effective than monotherapy in suppressing viral replication and may decrease or delay the incidence of drug resistance.

Viral features of lamivudine resistant hepatitis B genotypes A and D

Viral differences among lamivudine resistant hepatitis B (HBV) genotypes have not been yet investigated. Therefore, we analyzed the characteristics of these viral strains in vivo. Forty-one patients carrying lamivudine resistant HBV were enrolled. Twenty-six patients (63%) carried resistant HBV genotype A (group A) and 15 patients (37%) carried resistant HBV genotype D (group D). The rate of reverse transcriptase 204I mutants was significantly higher in group D (67%) compared with group A (19%), whereas rt204V mutants (81% in group A vs 33% in group D; P =.006) and rt180M mutants (81% in group A vs 40% in group D, P =.015) prevailed in group A. The median time of shift from rt204I to rt204V mutants was significantly shorter in group A (4 months in group A, >12 months in group D, P <.001). Additional resistance associated mutations were detected exclusively in group D (P =.004). In a multivariate analysis, HBV genotype (P =.039) and pretreatment serum HBV DNA (P =.001) were independently associated with emerging rt204I or rt204V mutants, respectively. Serum HBV copy numbers after emergence of resistance were higher in group A (mean log(10) 6.99 copies/ml; range 3-9) compared with group D (mean log(10) 6.1 copies/ml; range 3.3-8; P =.04). There was no difference between both groups regarding core promoter/precore mutations, viral turnover, and number of flares or disease progression during follow-up. In conclusion, the mutational pattern during selection of lamivudine resistant HBV strains differs between genotypes A and D. This may have consequences for a salvage regimen initiated for treatment of lamivudine resistant HBV.

Determinación del genotipo del virus de la hepatitis B y detección de mutaciones de resistencia al tratamiento con lamivudina

OBJECTIVES

To determine hepatitis B virus (HBV) genotypes in southern Seville (Spain) and investigate the development of lamivudine-resistance mutations by using a hybridization technique with specific probes and by comparing the results with those of the direct sequencing technique. To evaluate the temporal relationship between variations in the level of HBV-DNA and detection of mutant variants. To analyze the influence of several genotypes on the pattern of mutations developed and on values of viral load and alanine aminotransferase (ALT) after their development.

PATIENTS AND METHOD

In 37 patients with chronic HBV infection, HBV genotype was determined using the LiPA technique. In 10 of these patients undergoing lamivudine treatment for a mean of 19.2 months, the development of lamivudine-resistant mutations was investigated. In these 10 patients, the LiPA technique was compared with direct sequencing. During lamivudine treatment, we determined HBV-DNA by polymerase chain reaction (PCR) and ALT every 3-6 months.

RESULTS

The most frequent genotypes were D (45.9%) and A (18.9%); 2 patients were genotype B while 18.9% had mixed genotypes. Sequencing showed identical results except in one mixed genotype. Mutations were found in 60% of the cases. The results of sequencing were in agreement, except in the detection of mixed populations composed of mutants and wild-type (WT). Patients with genotype A showed the pattern M204I+WT in the first 12 months and those with genotype D showed the pattern L180M+M204V with or without WT at 18 months. In 5/6 cases, an increase of > 1 log10 in HBV-DNA was observed 3-8 months before the mutation was detected by LiPA. In patients with genotype B, levels of HBV-DNA and ALT after the development of mutations was lower than basal levels and was also lower than those in patients with genotypes A and D.

CONCLUSIONS

The LiPA technique for determination of HBV genotype and detection of lamivudine-resistance mutations shows excellent correlation with the most complex sequencing technique. Genotype D predominates in southern Seville. During lamivudine treatment, an increase in the level of HBV-DNA detected by PCR predicts the development of mutations before these are demonstrated by LiPA.

Complete genome sequence and phylogenetic analysis of hepatitis B virus (HBV) isolates from patients with chronic HBV infection in Korea

Although there is a report of high rate of hepatitis B virus (HBV) infection in South Korea, only a few entire genome sequences of HBV isolates from Korea have been reported. To obtain the complete nucleotide sequence of the Korean HBV, viral DNA was extracted from sera of Korean patients with chronic HBV infection who have not been exposed to any antiviral treatment. Complete genomic sequences were determined on three Korean HBV isolates. The entire genomic length of Korean HBV isolates, designated as KUHB84, KUHB81, and KUHB95, was 3,215 base pairs. No deletions and insertions were observed. Core promoter mutations (T1762/A1764) were detected in two isolates, KUHB84 and KUHB95. Phylogenetic analysis based on the entire genomic sequences showed that the Korean HBV isolates were genotype C and related closely to the Japanese HBV.

Rapid and sensitive assays for determination of hepatitis B virus (HBV) genotypes and detection of HBV precore and core promoter variants

Hepatitis B virus (HBV) genotypes may influence HBeAg seroconversion rates, mutational patterns in the precore (PC) and core promoter (CP) regions, severity of liver disease, and response to antiviral treatment. Development of rapid, simple, and standardized assays to detect viral genotypes and common mutations in the PC and CP regions can accelerate research on the clinical significance of these variants. We aim to assess the accuracy of a line probe assay in determining HBV genotypes and detecting HBV PC and CP variants. HBV genotypes in 701 patients and PC and CP variants in 600 patients with chronic HBV infection from China and the United States were studied using the INNO-LiPA assay. All but one (99.9%) sample were classified by the genotyping assay. All eight genotypes, i.e., A to H, were found. The INNO-LiPA genotyping assay results were completely concordant with those of sequencing. Using the INNO-LiPA PC assay, 99.8 and 94.7% samples were classifiable in the PC and CP regions, respectively. The PC assay results were completely concordant with those of sequencing in all samples that showed either wild-type or variant sequence. The line probe assay was more sensitive in detecting mixtures than was direct sequencing. By INNO-LiPA, only 50 and 27% of the samples, with mixed wild-type and variant sequence in the PC and CP region, respectively, showed mixed sequence by direct sequencing. INNO-LiPA is rapid, sensitive, and reliable-thus enabling accurate determination of HBV genotypes and detection of PC and CP variants in a large population of patients.