Phenotypic and genotypic testing of HSV-1 resistance to antivirals.

Resistance testing of antivirals to herpes simplex virus type 1 can be done by phenotypic and genotypic methods. The determination of a resistant phenotype is based on the calculation of inhibitory concentrations for the antiviral drug, which should be tested. The main advantage is a clear interpretation of laboratory findings, but the method is time consuming and a considerable experience is required for handling infectious virus. Genotypic resistance testing is based on the detection of resistance-related mutations in viral genes encoding the thymidine kinase and DNA polymerase by means of amplification and sequencing. This approach has the advantage of being faster, but only frameshift mutations and stops of translation can be interpreted without doubt and numerous amino acid substitutions are diagnostically less conclusive.