Hepatitis B Virus, Genotypes and Subtypes

Abstract

Hepatitis simply means inflammation of liver. This word came from heap: the Latin for liver and “titis” means inflammation. In addition to viruses, many varieties of agents can cause hepatitis such as bacteria, parasites, fungi and chemical agents including drugs, toxins and alcohol. Hepatitis B virus is classified as an Orthohepadna virus (Genera) within the family Hepadnaviridae. This family Includes the wood chuck hepatitis virus WHV, the duck hepatitis virus DHBV, and several other avian and mammalian variants. The human HBV has been shown to infect chimpanzees, Barbary macaques and tree shrews. All hepadnaviridae have similar to hepatotropism and life cycles in their hosts. HBV infection is a global health problem which is 50–100 times more infectious than HIV. Approximately 400 million people are carriers of chronic liver disease every year due to consequences of the disease. Not only HBV can infect hepatocytes but also infects in extrahepatic sites including lymph nodes, bone marrow, circulating lymphocytes, spleen and pancreas. Hepatitis B virus can occur as an acute or chronic disease. Previously, HBV genotypes have been classified into eight genotypes (A-H) and because of genome diversity is a hallmark of HBV virus allowed its classification into (10) genotypes (A–J). The clinical relevance of such genotype is yet unclear. Detection of HBV genotype is very important to clarify the pathogenesis, rout of infection and virulence of the virus. The major classification of HBV subtype is sorted into 4 subtypes or serotypes (adr, adw, ayr, and ayw). The four possible combinations define the major subtypes and additional amino acids contribute to immunogenicity. These subtypes can be further classified into (9) serotypes (adw2, adw4q-, adrq+, adrq-, ayw1, ayw2, ayw3, ayw4 and ayr). Epidemiologic studies found that the prevalence of these serotypes varies in different parts of the world.