Characterisation of acyclovir-resistant and -sensitive clinical herpes simplex virus isolates from an immunocompromised patient.

A detailed study was made of herpes simplex virus type 1 (HSV-1) isolates from an immunocompromised patient whose infection became resistant to acyclovir (ACV) during a prolonged course of oral treatment. Three HSV isolates and 33 virus clones derived from them were characterised. The development of clinical resistance correlated with the emergence of thymidine kinase (TK) defective strains. The ACV-sensitive strains studied contained a small proportion of insensitive virus. The resistant isolate contained 0.6% of TK-positive virus which was sensitive to a relatively low concentration of ACV.