Hepatitis B virus genotypes: comparison of genotyping methods.

There are eight genotypes of HBV designated A to H based on greater than 8% nucleotide variation over the entire genome. Hepadnaviruses infecting primates like the chimpanzee, orangutan and gibbon are very similar and can be regarded as genotypes of HBV. The eight genotypes of HBV show a distinct geographical distribution and influence the course of disease and the prognosis of treatment. Due to the variability of HBV, diagnostic procedures risk giving false-negative results or reporting an inaccurately low quantitative result. Thus, the variability of HBV genotypes can influence the interpretation of diagnostic data and the therapeutic decisions thereof in an unwanted way. HBV genotypes differ in the length of their genomes. The old system of numbering HBV nucleotides from the start of a non-conserved EcoRI site in the genome leads to difficulties in comparing nucleotide positions between genotypes. A numbering system is presented which avoids this problem. In addition we discuss the currently available methods for genotyping HBV.