Improved yields and assay of simian varicella virus, and a comparison of certain biological properties of simian and human varicella viruses

Abstract

Studies were performed to define conditions under which propagation, assay and stabilization of the Delta herpesvirus (DHV) strain of simian varicella virus might be improved, and to compare biological properties of DHV with those of human varicella zoster virus (VZV). A mycoplasma contaminant was successfully eliminated from the DHV seed virus by treatment with a specific anti-serum. DHV was found to replicate more efficiently in the BS-C-1 line of African green monkey kidney cells than in Vero cells, and seed virus preparations in the form of virus-infected cells were produced which had infectivity titers greater than or equal to 1 X 10(6) p.f.u./ml. Greater yields of virus were produced in cultures infected as dispersed cells than as preformed monolayers. Infectious DHV could be released from host cells by sonic treatment of heavily infected cultures at 48 h post infection. Certain agents reported to enhance replication of herpes viruses (caffeine, carbaryl, the tumor promoter 12-0-tetra-decanoyl-phorbol-13-acetate, and DEAE-dextran) had no enhancing effect on replication of DHV. However, DEAE-dextran in the maintenance medium enhanced spontaneous release of DHV into culture fluids. Plaquing efficiency and plaque size of DHV were greater in BS-C-1 than in Vero cells, and plaque assays and plaque reduction neutralization tests were developed in this cell system using a solid overlay medium with neutral red vital stain. Neutralization of DHV was markedly enhanced by fresh guinea pig complement. The newly developed neutralization test demonstrated more vigorous antibody responses to DHV in active and latent VZV infections than were demonstrated with previous procedures. In addition to their preferential growth in monkey and human cells respectively, DHV and VZV were found to differ markedly in their rates of attachment to host cells, with DHV requiring over 6 h of adsorption, while VZV adsorption was essentially complete at 1 h. Also, cell-free DHV was much more resistant than cell-free VZV to repeated cycles of freezing and thawing.