Kramvis A
Hepatitis Virus Diversity Research Unit, Department of Internal Medicine, School of Clinical Medicine, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa.
S Afr Med J. 2018 Aug 8;108(8b):17-21. doi: 10.7196/SAMJ.2018.v108i8b.13495.
Hepatitis B virus (HBV), a DNA virus, replicates via an RNA intermediate, through reverse transcription catalysed by the viral polymerase that lacks proof reading ability. Thus sequence heterogeneity is a feature of HBV being classified into at least 9 genotypes and over 35 subgenotypes. Africa has a high diversity of genotypes/subgenotypes, with distinct geographical distributions. Genotype A is found mainly in south-eastern Africa, E in western and central Africa and D prevailing in northern Africa. Outside Africa, subgenotype A2 prevails and A1 in Africa, which was the most probable source of its dispersal to Asia and Latin America, as a result of slave and trade routes. Genotype E is also an African strain with low genetic diversity, intimating a recent emergence of 200 years or less, with its dispersal outside Africa occurring as a result of modern human migrations. Carriers of subgenotype A1 and genotype E display unique clinical features. A1-infected individuals have low viral loads, low frequency of HBeAg-positivity, horizontal transmission of HBV, higher levels of liver damage and a higher risk of developing hepatocellular carcinoma. In contrast, individuals infected with genotype E have high viral loads, high frequency of HBeAg-positivity and transmit HBV perinatally. Although 15% of HBV infections in HIV-infected Africans are HBsAg-negative, the true occult phenotype of low viral loads is found in only 7% and 65% of individuals infected with subgenotype A1 and genotypes E (or D), respectively. Molecular and functional characteristics of these African HBV strains can account for their different clinical manifestations.
乙型肝炎病毒（HBV）是一种DNA病毒，通过RNA中间体进行复制，由缺乏校对能力的病毒聚合酶催化逆转录。因此，序列异质性是HBV的一个特征，它至少可分为9个基因型和35个以上的亚基因型。非洲的基因型/亚基因型具有高度多样性，且有明显的地理分布。A型主要见于非洲东南部，E型见于非洲西部和中部，D型在北非占主导。在非洲以外，A2亚基因型占主导，而在非洲A1亚基因型占主导，由于奴隶贸易路线，它很可能是传播到亚洲和拉丁美洲的源头。E基因型也是一种非洲毒株，遗传多样性较低，表明它是在近200年或更短时间内出现的，其传播到非洲以外地区是现代人类迁徙的结果。A1亚基因型和E基因型的携带者表现出独特的临床特征。感染A1的个体病毒载量低，HBeAg阳性频率低，HBV水平传播，肝损伤程度较高，患肝细胞癌的风险也较高。相比之下，感染E基因型的个体病毒载量高，HBeAg阳性频率高，且通过母婴传播HBV。尽管在感染HIV的非洲人中，15%的HBV感染是HBsAg阴性，但真正病毒载量低的隐匿表型仅分别见于7%感染A1亚基因型和65%感染E（或D）基因型的个体中。这些非洲HBV毒株的分子和功能特征可以解释它们不同的临床表现。
