Synthesis of coreless, probably defective virus particles in cell cultures infected with rotaviruses.

PK-15 cells infected with pig and lamb rotavirus strains which were not adapted to serial growth in cell cultures were examined by electron microscopy. A major difference between virus morphogenesis in the initial passage in PK-15 cells and in intestinal epithelial cells was the generation of large numbers of coreless virus particles in PK-15 cells. The numbers of coreless particles increased with increasing multiplicity of infection. Infectious virus was synthesized in PK-15 cells, but a variable decrease in infectivity titre occurred between 12 and 24 hours after infection. It is suggested that synthesis of defective interfering particles or an inhibitory substance such as interferon might account for this decrease.