PLAQUE DIFFERENTIATION AND REPLICATION OF VIRULENT AND ATTENUATED STRAINS OF MEASLES VIRUS

Abstract

Plaque formation by strains of measles virus in a stable line of African green monkey kidney cells (BSC-1) is characterized by development of large plaques (> 1 mm) within 4 days after inoculation of the cultures with the virulent Edmonston strain or by small plaques (<1 mm) after inoculation with the attenuated Edmonston strain of virus. Plaque formation by measles virus is not influenced by iodo-deoxyuridine, cytosine arabinoside, isatinthiosemicarbazone, strep-tonigrin, actinomycin D, or mitomycin C. The predominant cytopathic effect observed with both strains is the formation of large, multinu-cleatedgiantcells. Development of the giant cells is correlated with development of virus antigen and synthesis of infectious virus. Synthesis of virus is similar at 34 and at 37 C. Appearance of intra-cellular virus precedes release, and is later in the attenuated virus-infected cells than in cells infected with the virulent strain. With the virulent strain, equal concentrations of intra- and extracellular virus are found but, with attenuated virus, only a small fraction reaches the extracellular fluids, and more than 95% of the newly synthesized virus remains cell-associated.