The DNAs of 20 strains of varicella-zoster virus (VZV) isolated from epidemiologically unrelated individuals, and of 15 strains isolated from vesicles of vaccinees with varicella or zoster after vaccination, were compared by restriction enzyme cleavage using I. Differences were found in the sizes of the I-F, -G and -K fragments of the wild strains. The gel migration patterns of the I-F and -G fragments, but not of the I-K fragment, were polymorphic in the different strains isolated from the vaccinees. The effects of serial passages and in humans on the genome stability of VZV were investigated by I analysis. The DNA profiles of the I-K fragments from six isolates recovered from room-mates infected in a single outbreak were identical, but the mobilities of their I-F and -G fragments varied. The DNA profiles of the Oka vaccine virus after 10 and 85 passages in human embryo cells differed only in the I-F fragment. The profiles of these fragments in DNA derived from two isolates obtained at different times from a vaccinee with varicella followed by zoster were compared with those of the Oka (parental) and Oka (vaccine) strains, and identical results were obtained for the two viruses. In addition, the same DNA profiles of I fragments were obtained from three sequential isolates from one person and also from two isolates from another with varicella and zoster. Thus, it was concluded that: (i) three variable fragments (I-K, -F and -G) were not changed in the DNAs of isolates derived from the same patient; (ii) I-K was stable both on passage and after human transmission in the case of the same outbreak, but was different among all wild-type strains isolated in epidemiologically unrelated outbreaks; (iii) I-F was very unstable both on passage and in human infections by either vaccine or wild-type strains; (iv) I-G was not influenced by passage but varied among wild-type strains. Using physical maps of VZV DNA established by others, three variable regions on the viral genome were identified. One was located near the 0.16 coordinate, which is covered by I-K (variable region I, VRI). Another was represented by I-F (VRII), the most unstable fragment, and mapped at about the 0.35 coordinate. The third was VRIII near the right terminus, covered by I-G.


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