Hepatitis B Viruses

About 2 billion people have been infected with hepatitis B virus (HBV) worldwide. Among them, 240 million are chronic HBV carriers. Overall, almost half the global population still lives in areas where HBV infection is highly endemic, such as in Asia and Africa. The prevalence of chronic HBV infection has declined dramatically in past decades as the result of universal vaccination programs. In Latin America (LA), most countries have middle or low prevalence, despite the persistence of areas of high prevalence such as in the Amazon region and some isolated Afro-descendant communities. HBV is the prototype of the Hepadnaviridae family, the sole family that comprises partially double-stranded circular DNA viruses of animals that replicate through their reverse transcription. HBV isolates have been classified into at least eight genotypes (HBV/A to HBV/H), most of them subdivided into sub-genotypes. HBV genotypes have a distinct geographic distribution around the world. Two genotypes, HBV/F and HBV/H, originated from the Amerindian population, circulate in LA. The other HBV genotypes circulating in LA were introduced by European colonizers (HBV/A2 and HBV/D) and African slaves (HBV/A1). These genotypes/sub-genotypes may have differential biological behaviors when compared to HBV genotypes from other parts of the world. The fact that HBV/H and HBV/F are the most divergent among human genotypes justifies deeper epidemiological studies, which could contribute to the understanding of HBV features of importance for clinical outcome, response to treatment, and immunization strategies.