Hepatitis B is a potentially life-threatening liver infection caused by the hepatitis B virus (HBV). Despite being preventable with a vaccine, hepatitis B remains a significant public health concern, particularly in low- and middle-income countries, including those on the African continent. To better understand the distribution and prevalence of HBV genotypes on the African continent, a systematic review with meta-analysis was conducted, covering data from 1997 to 2021. In this article, we explore the findings of this study, which shed light on the genetic diversity of HBV and have important implications for diagnosis, treatment, and prevention measures in Africa.
Hepatitis B virus (HBV) is a major public health concern worldwide, with approximately 250 million people chronically infected and at risk of developing liver cirrhosis and hepatocellular carcinoma (HCC). HBV is a highly diverse virus with eight distinct genotypes (A-H) that differ by more than 8% at the nucleotide level. The geographic distribution of HBV genotypes is complex and reflects the ancient and recent patterns of human migration and dissemination.
Several studies have investigated the distribution and diversity of HBV genotypes in different populations and regions. A study by Matsuura et al. found that the distribution of HBV genotypes among patients with chronic infection in Japan is shifting toward an increase of genotype A. Similarly, a study by Wolf et al. showed that genotype A is spreading in Brazil and the Americas. In West Africa, a phylogenetic analysis of the precore/core gene of HBV genotypes E and A revealed new subtypes, mixed infections, and recombinations.
In Indonesia, Thedja et al. discovered a new subgenotype, B9, and Toyé et al. identified an expanding clade of subgenotype A4. In China, Liu et al. characterized a novel HBV subgenotype, B10, among chronic hepatitis B patients in Yunnan. Furthermore, Lin et al. and Li et al. used phylodynamic analysis to trace the origin and dispersal of HBV genotype C in East Asia and globally, respectively. Yuen et al. used HBV genomes to trace ancient human migrations into Sahul, which includes Australia and New Guinea, and to study the phylogeography of HBV in the region.
Other studies have investigated the diversity and evolution of HBV genotypes in specific populations such as Papua, Indonesia, and the primitive tribes of Arunachal Pradesh in India. Haldipur et al. found that genotype I of HBV circulates in east Xishuangbanna, China, and Tatematsu et al. identified a genetic variant of HBV divergent from known human and ape genotypes isolated from a Japanese patient. In addition, Velkov et al. examined the global occurrence of clinically relevant HBV variants and the distribution of HBV genotypes worldwide.
The geographic distribution of HBV genotypes has important clinical implications. For example, some studies have shown that genotype B is associated with a better response to interferon therapy than genotype C in patients with chronic hepatitis B. Similarly, the prognosis of chronic hepatitis B and the risk of HCC vary among different HBV genotypes and subgenotypes. Patients infected with genotype A and its subgenotypes have a higher risk of HCC than patients infected with other genotypes, whereas patients infected with genotype D and its subgenotypes have a higher risk of cirrhosis and HCC than patients infected with other genotypes. Therefore, the determination of HBV genotypes and subgenotypes is essential for the management and treatment of chronic hepatitis B.
Current clinical practice guidelines recommend the use of antiviral therapy for patients with chronic hepatitis B who meet certain criteria, regardless of the HBV genotype. However, the choice of antiviral therapy may depend on the HBV genotype and drug resistance profile. Therefore, the accurate determination of HBV genotypes and subgenotypes is crucial for guiding the selection and monitoring of antiviral therapy.
In conclusion, the geographic distribution and diversity of HBV genotypes and subgenotypes reflect the complex and dynamic patterns of human migration and dissemination. The determination of HBV genotypes and subgenotypes has important clinical implications for the management and treatment of chronic hepatitis B. Further studies are needed to improve our understanding of the diversity and evolution of HBV and to develop more effective strategies for the prevention and control of HBV infection and its associated diseases.
