Improved yields of cell-free varicella-zoster virus

Systematic studies on the replication of varicella-zoster virus in infected human fetal diploid lung cells have defined more optimal conditions for infection and harvesting of cultures and have led to the production of cell-free virus preparations with infectivity titers of greater than or equal to 10(6) plaque-forming units per ml. The highest yields of cell-free virus were obtained by (i) sonic treatment of the cellular phase of cultures inoculated with trypsin-dispersed infected cells at ratios of 1 infected cell to 6 to 10 uninfected cells in the monolayer and (ii) harvesting cells after 24 to 36 h of incubation at 36 degrees C. At this time the cultures showed minimal viral cytopathic effect. Spread of infectivity occurred much more rapidly in cultures inoculated with whole infected cells than in those infected with cell-free virus. Complement-fixing antigens with improved titers of greater than or equal to 1:128 were prepared from varicella-zoster virus-infected cell cultures in the same manner as cell-free virus, but harvested after 3 to 4 days of incubation when the cultures showed an advanced cytopathic effect.