Genetic heterogeneity of hepatitis viruses and its clinical significance.

The genetic heterogeneity of hepatitis B virus (HBV) (8 genotypes A-H) has been applied for tracing the route of HBV transmission and the geographical migration of HBV carriers but it also appeared to have clinical implications. The secondary structure of e encapsidation signal could explain why the precore mutant virus prevails in Mediterranean countries, where genotype D is most prevalent, while the wild type virus is frequent in Western countries, where genotype A is most prevalent. There is increasing evidence that patients infected with genotype C have more severe outcome of chronic liver disease than those infected with genotype B. Genotype B was associated with fulminant hepatitis and more severe episodes of acute exacerbation of chronic HBV infection. Patients infected with genotype B appeared to seroconvert earlier than those infected with genotype C. The hepatitis delta virus (HDV) has 3 genotypes (I, II, III) which are associated with different disease patterns. Genotype III is the most distantly related HDV genotype and is associated with the most severe outcome while genotype II with relatively mild liver disease. The most geographically widespread genotype is I and is associated with a broad spectrum of chronic liver disease. The hepatitis C virus (HCV) displays high genetic heterogeneity with six genotypes (1-6), multiple subtypes and quasispecies. This viral diversity has epidemiological and clinical implications and has been associated with the severity of liver disease, prognosis, response to treatment and failure to generate an effective protective vaccine. HCV genotype 1 is the predominant genotype in Western countries and has been associated with a low response rate to interferon-alpha (IFN-alpha) or to the combination of ribavirin and IFN-alpha. Consequently the duration of treatment has been tailored according to HCV genotype.