Varicella zoster virus deoxythymidine kinase is present in serum before the onset of varicella.

A sensitive enzyme assay with 125I-iododeoxyuridine as substrate and cytidine triphosphate as phosphate donor was used for the direct detection of varicella zoster virus (VZV) deoxythymidine kinase (TK) in human serum. Sera sampled during the incubation period of varicella from 2 patients, a 42-year-old man and his 11-year-old son, have been analysed for TK activity. A simultaneous increase in cellular and VZV TK activity, starting 5 to 3 days before the onset of clinical varicella, was observed.