Novel hepatitis B virus strain developing due to recombination between genotypes H and B strains isolated from a Japanese patient

Evolutionary history of hepatitis B virus genotype H

Hepatitis B virus genotype H (HBV-H) molecular evolution was studied by comparing all published whole-genome sequences. Bayesian coalescent analysis was performed to estimate phylogenetic relationships, time to the most recent common ancestor (tMRCA), and viral population dynamics along the time. Phylogenetic tree demonstrated two main clades or lineages: HBV-H I (with sequences from Central and North America) and HBV-H II (with sequences from North and South America, and Asia). HBV-H II had more genome sequences (n = 26; 83.9%), including one specific subclade with all sequences outside of the Americas. Overall HBV-H tMRCA dated back to 1933 (95% highest posterior density interval [HPD 95%]: 1875-1957) with a very probable origin in Mexico and posterior dissemination to other American and Asian countries. The temporal analysis demonstrated that HBV-H I spread only in Mexico and the neighbor country of Nicaragua probably in the 1960s to the 1970s (1968; HPD 95%: 1908-1981), while HBV-II disseminated to other American and Asian countries around one decade later (1977; HPD 95%: 1925-1985). The phylogeographic analysis reinforced the Mexican origin of this genotype. The whole HBV-H population increased from the 1980s to the 2000s. In conclusion, HBV-H has two main lineages with a common origin in Mexico approximately nine decades ago.

Chronic hepatitis caused by hepatitis C virus showing a discrepancy between serogroup and genotype because of intergenotypic 2b/1b recombination: A pitfall in antiviral therapy with direct-acting antivirals

A 40-year-old male patient with virologic relapse after daclatasvir plus asunaprevir therapy for a serogroup 1 hepatitis C virus (HCV) infection visited our hospital for retreatment. Virologic examinations revealed that a genotype 2b HCV strain carrying both NS3-S122N / D168A and NA5A-R30Q / L31M / Q54H / Y93H mutations had relapsed. The patient received sofosbuvir plus ribavirin therapy, but virologic relapse occurred once again. Sequencing of the HCV genome clarified an intergenotypic recombination of 2b and 1b with an estimated crossover point between nucleotides 3114 and 3115, corresponding to the N-terminal end of the NS3 region (DDBJ/EMBL/GenBank databases accession no. LC273304). The NS5B-S282T mutation was not detected in the HCV strain, and resistance-association substitutions in the NS3 and NS5A regions were similar to those at baseline. Direct sequencing of the core and NS4A regions corresponding to the targeting sites of genotyping and serogrouping, respectively, is useful to determine the combination of direct-acting antivirals when a discrepancy is observed between the serogroup and genotype of HCV strains.

Estimating numbers of persons with persistent hepatitis B virus infection transmitted vertically and horizontally in the birth cohort during 1950-1985 in Japan

AIM

We estimated numbers of persons, born between 1950 and 1985 in Japan, who were persistently infected with hepatitis B virus (HBV) through vertical and horizontal infections.

METHODS

HBV carrier rates with vertical and horizontal infections were computed using sex- and age-specific prevalence rates of hepatitis B surface antigen (HBsAg) and hepatitis B e-antigen (HBeAg) by mathematical model. Probabilities of vertical HBV transmission in babies born to carrier mothers with and without HBeAg were presumed to be 90% and 10%, respectively.

RESULTS

HBV carrier rates with vertical infection stayed contrast at approximately 0.3% in birth cohorts through 36 years (1950-1985), both in men and women. By a remarkable constant, HBV carrier rates with horizontal infection decreased steadily from 1.43% to 0.10% in men and from 0.95% to 0.03% in women. The estimated total number of HBV carriers born between 1950 and 1985 was 522 500 (355 488-693 606). Of them, the numbers of HBV carriers with vertical and horizontal infections were 197 574 (149 505-288 709) and 324 926 (205 983-404 896); they accounted for 37.81% and 62.19%, respectively, with a ratio of 1:1.64. The ratio between vertical and horizontal infections was 1:2.20 in men and 1:1.06 in women.

CONCLUSION

Vertical HBV infection had stayed constant until immunoprophylaxis of mother-to-baby transmission was implemented in 1986 in Japan. In contrast, horizontal HBV infection decreased over years. The decrease would be due to many factors, including improved socioeconomic environments, advanced medical maneuvers and equipment, and careful vaccination procedures.

Molecular epidemiology of hepatitis B virus in Asia

Although safe and effective vaccines against hepatitis B virus (HBV) have been available for three decades, HBV infection remains the leading cause of chronic hepatitis, cirrhosis and hepatocellular carcinoma (HCC) worldwide, especially in Asian countries. HBV has been classified into at least 9 genotypes according to the molecular evolutionary analysis of the genomic DNA sequence and shown to have a distinct geographical distribution. Novel HBV genotypes/subgenotypes have been reported, especially from Southeast Asian countries. The clinical characteristics and therapeutic effectiveness of interferon (IFN) and nucleos(t)ide analogues vary among different HBV genotypes. Mutations at T1653C in subgenotype C2 from Japan and South Korea, C/A1753T and C1858T in subgenotype C1 from Vietnam, and C1638T and T1753V in subgenotype B3 from Indonesia were reported to be associated with advanced liver diseases including HCC. Genotype distribution in Japan has been changed by an increasing ratio of subgenotype A2 in chronic hepatitis B. While a large number of epidemiological and clinical studies have been reported from Asian countries, most of the studies were conducted in developed countries such as Taiwan, China, South Korea and Japan. In this review, the most recent publications on the geographical distribution of genetic variants of HBV and related issues such as disease progression and therapy in Asia are updated and summarized.