Background: The thymidine kinase (TK) and DNA polymer- ase (pol) genes of herpes simplex virus type-1 (HSV-1) and type-2 (HSV-2) are important targets for genotypic determination of HSV resistance to antiviral drugs

Background: The thymidine kinase (TK) and DNA polymerase (pol) genes of herpes simplex virus type-1 (HSV-1) and type-2 (HSV-2) are important targets for genotypic determination of HSV resistance to antiviral drugs. The knowledge of gene polymorphism is an absolute requirement for the correct interpretation of genotypic findings. Methods: In this study, the natural polymorphism of TK and DNA pol genes was examined by DNA sequencing in 56 HSV-1 and 12 HSV-2 strains sensitive to acyclovir. Results: In 56 HSV-1 strains, 26 different nonsynonymous polymorphism-associated mutations were detected in the TK gene. To our knowledge, 8 of them have never been reported in the literature. In the TK gene of 12 HSV-2 strains, 6 polymorphism-related non-synonymous mutations were observed, whereas there was 1 novel mutation in 1 strain. The DNA pol gene of 53 HSV-1 isolates contained 47 distinct polymorphism-associated amino acid substitutions and 11 substitutions were found in the DNA pol gene of 12 HSV-2 strains. Altogether, 31 novel substitutions could be identified in the DNA pol gene of HSV-1 and 3 in HSV-2 strains. In these strains, any resistance to foscarnet was excluded. Conclusions: The 43 novel non-synonymous mutations enrich the knowledge about the natural genetic polymorphism of TK and DNA pol in clinical HSV strains. The findings have to be considered for genotypic analysis of HSV in case of clinical resistance.