Laboratoire d’expertise en virologie, Centre national de référence pour les hépatites B et C en transfusion, Institut national de la transfusion sanguine, 6, rue Alexandre Cabanel, 75015 Paris
The genetic diversity of hepatitis B virus (HBV) was defined on the basis of the characterisation of the major determinants in the antigenic loop of HBs antigen (Ag). Historically, nine subtypes were defined. Recently, based on sequence analysis, HBV genomes have been classified into eight genotypes (A-H) which present distinct geographical distributions. Genetic mutants may have a selective advantage in patients treated with passive or active immunization (hepatitis B immune globulin or vaccine). Anti-viral treatment can be responsible for the emergence of escape mutants with resistant mutations in the polymerase gene. These substitutions can lead to changes on HBsAg structure. The lack of detection of several envelope mutant viruses by some commercial HBsAg assays has been demonstrated. Substitutions involving precore/core region have also been found to prevent HBeAg synthesis.