[Acute and chronic Lassa virus infection of Vero cells]

Acute and persistent infections of Vero cells with a cloned Lassa virus were studied. After acute infection at a multiplicity of 2 PFU/cell the latent period was 12-16 hrs and the maximum yield of virus particles in the growth medium was obtained 28-32 hours postinfection. A persistently infected cell line was established by inoculating Vero cells with the cloned Lassa virus followed by subcultivation of the infected cells. The infected cells underwent 36 passages. Lassa virus production by the infected cells followed a cyclic pattern varying from 10(2) to 10(5) PFU/ml. Neither the plating efficiency of the virus nor its growth curves changes at 35 degrees C and 39 degrees C. The replication of the cloned virus in infected cells (superinfection) was markedly depressed in comparison to that of normal Vero cells infected with Lassa virus. The role of defective interfering particles in the establishment of persistent infection is discussed.