The DNA sequence analysis of the viral genome led to the identification of 4 different genes, called C, S, P and X encoding AgHBc/HBe, HBsAg, polymerase and HBx proteins respectively. The expression of these genes is adjusted by 4 promoters (S1p, S2p, Cp and Xp) and 2 Intensificatori (enhancer I, II) 1. The Filogenetică analysis led to the HBV classification in 9 genotypes (called A-I) which differs from each other in the proportion of > 7.5% at the level of The nucleotide sequences of the entire genome, with the indication that there could still be a genotype J, which was isolated from one individual. In addition, in genotypes A-D, F, H and I have been described at least 35 subgenotypes which differ between them in the proportion of 4 to 8% 2.
The 9 genotypes present a distinct geographic distribution. Genotype A is prevalent in north-western Europe, North America and Africa, genotypes B and C prevail in Asia, genotype D has a ubicuitară distribution, but prevails in the Mediterranean area. Genotype E is met in Africa, genotype F in Aboriginal populations in South America, and genotype H is limited to Amerindian populations in Central America. Genotype G may cause chronic infection only in the presence of other genotypes, in particular genotype A and is transmitted predominantly by homosexual contact; It was identifcat in subjects from USA, Mexico, Germany, Italy, Great Britain, France. Genotype I was described in people from Laos, Vietnam and India being associated with perinatal transmission. "Genotype J" was isolated from a Japanese male with hepatocellular carcinoma who lived in Borneo2 for a long time.
- Margaret James Koziel, Chloe Lynne Amirhossein. Hepatitis B virus and Hepatitis D virus. In Mandell, Douglas, and Bennett ' SPrinciples and Practice of Infectious Diseases, 7th edition, Churchill Livingstone, Elsevier, 2010, 2059-2064.
- Kramvis A. Genotypes and genetic variability of hepatitis B virus. Intervirology. 2014; 57 (3-4): 141-50.
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