Establishment and maintenance of persistent infection by the Phlebovirus Toscana in Vero cells.

Persistent infections were established by serial undiluted passages of the Toscana virus of the genus Phlebovirus in Vero cells. Persistence was maintained through more than 70 passages over a period of 2 years. The persistently infected cells were morphologically similar to the parental Vero cells and released variable amounts of infectious virus. A small percentage of the persistently infected cells produced infectious virus while a larger percentage was shown to possess viral antigens by fluorescent antibody staining. Temperature sensitivity and host cell interferon production were not involved in establishment or maintenance of persistence. The persistently infected cultures were resistant to superinfection with homologous Toscana virus, but they were susceptible to superinfection with heterologous viruses of different genera or families. Toscana virus persistently infected cells showed a selective graded resistance to the replication of other Phleboviruses. Additionally, the virus from persistently infected cells interfered with the replication of standard Toscana virus when they co-infected normal cells. The characteristics of the persistently infected cultures are compatible with some of the characteristics described for the persistence mediated by defective-interfering particles of other viruses.