Abstract Advances in molecular diagnostic technology make it possible to accurately measure viral loads and this has allowed the detailed study of viral dynamics of HIV, hepatitis C virus (HCV) and hepatitis B virus (HBV). Following antiviral therapy, there are at least two phases of viral load decay: one corresponding to clearance of free virions and a second, slower phase corresponding to eradication of infected cells. Application of mathematical models allows for the assessment of antiviral efficacy and improved design of therapeutic regimens. The clinical application of these tools should help optimize patient outcome. Another advantage of molecular diagnostics is characterization of the heterogeneity of viruses in particular patient populations under selective pressure situations. The HBV can be classified into seven major genotypes (A–G) that have mainly a geographic distribution. Recent genotypic studies have revealed the clinical and therapeutic relevance of viral genotyping in HBV infections.
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