Recombination in Tissue Culture Between Varicella-zoster Virus Strains

Several clinical varicella-zoster virus isolates obtained during testing of a live varicella vaccine had DNA restriction fragment patterns resembling neither vaccine nor wild-type virus [Gelb et al., J Infect. Dis. 155, 633-640, 1987]. One explanation for these isolates was recombination in vivo. To determine if such recombination is likely, two strains of varicella-zoster virus, distinguishable by restriction endonuclease fragment size differences (wild-type strain EF and the OKA vaccine strain), were grown together in tissue culture. After three passages, the mixed infection virus was plaque-purified. DNA from about 13% of the plaque-purified isolates had one or more BglI fragments found in neither parental virus. Hybridization studies showed that isolates containing one of the new BglI fragments were recombinants of the two parental strains. The BglI restriction fragment pattern of these recombinants resembled those of the unusual varicella isolates from individuals either vaccinated with the live attenuated OKA varicella vaccine and later exposed to natural varicella, or simultaneously exposed to both a recent recipient of the vaccine and natural varicella.