4,5 Accordingly, HBV genotyping is still not CHIR-99021 research buy recommended as part of the management of chronic hepatitis B in regional guidelines.6–8 In this article, we describe recent advances in the impact of HBV genotype on the clinical outcomes and responses to antiviral treatments in chronic hepatitis B patients. In addition, the interactions between HBV genotype and other viral factors, such as viral load and viral mutants, will be reviewed. According to the homogeneity
of virus sequences, at least 10 HBV genotypes (A to J) and several subtypes have been defined by divergence in the entire HBV genomic sequences, respectively, >8% for genotypes and 4–8% for subtypes.9–11 Except for the newly identified genotypes I and J, the geographic and ethnic distributions of HBV genotypes and subtypes are well characterized (Table 1). Genotype A is highly prevalent in sub-Saharan Africa (subtype A1), Northern Europe (subtype A2), and Western Africa (subtype A3). Genotypes B and C are common in Asia. At present, genotype B is divided into B1–B6 subtypes. Among them, B1 is isolated in Japan, B2–5 are found in East Asia, and B6 is found in indigenous populations living in the Arctic, such as Obeticholic Acid nmr Alaska, Northern Canada and Greenland. Genotype C, including subtypes C1–C5, mainly
exist in East and Southeast Asia. Genotype D with subtypes D1–D5 is prevalent in Africa, Europe, the Mediterranean region and India. Genotype E is restricted to West Africa. Genotype F with 4 subtypes (F1–F4) is found in Central and South America. Genotype G has been reported in France, Germany and the United States. The eighth genotype, H, is found in Central America.4,9–13 Recently, genotype I, a novel inter-genotypic recombination among genotypes A, C, and G was isolated in Vietnam and Laos.14–16 The newest HBV genotype,
J, was identified in the Ryukyu islands in Japan, and this genotype has a close relationship with gibbon/orangutan genotypes and human genotype C.17 The correlation of HBV genotype distribution with modes of transmission was selleck products commented upon in our original landmark review in the Journal of Gastroenterology and Hepatology.4 For example, genotypes B and C are prevalent in highly endemic areas, such as Asian countries, where perinatal or vertical transmission plays an important role in spreading HBV, whereas the remaining genotypes are frequently found in areas where horizontal transmission (close personal conduct between young children, blood or sexual contamination between adults) is the main mode of transmission. Accordingly, genotyping HBV can serve as an epidemiologic tool for the investigation of maternal transmission, familial clustering and geographic distribution of HBV strains.18 The results of several studies indicate that HBV genotype can influence the short- and long-term outcomes of HBV infection (Table 2). Recent studies suggested that acute infection with HBV genotype A may increase the risk of progression to chronic infection.