Some characteristics of persistent rabies virus infection in cell cultures.

Fixed rabies virus strain M512 was shown to propagate in BHK cell cultures without interfering with cell growth. Virus specific antigen was detected in the cytoplasm of cells by immunofluorescence technique. A small amount of virus was detected in the supernatant fluid throughout a series of subcultures. The infectivity of the intracellular virus was not affected by the addition of antirabies serum in culture fluid through the extracellular spread of virus was inhibited at the 40th transfer of the infected BHK Cells suggesting the establishment of the persistent M512 infection. Ninety five percent or more cells after cloning from persistently infected cells possessed viral antigen. Based on cytopathic effect, BHK-M512 cells were resistant to superinfection with the homologous virus but were susceptible to the heterologous virus. Interferon was not detected in BHK-M512 cell cultures. The serially passaged BHK-M512 virus gradually decreased the virulence for mice after 40th subculture.