Molecular characteristics and clinical relevance of African genotypes and subgenotypes of hepatitis B virus
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.
A Kramvis, Hepatitis Virus Diversity Research Unit, Department of Internal Medicine, School of Clinical Medicine, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, South Africa
Full TextPDF (344KB)
Cite this article
Date published: 2018-08-08
Full text views: 551