Adaptation of the lapinized rinderpest virus to in vitro growth and attenuation of its virulence in rabbits.

A lapinized rinderpest virus, the L strain, which is virulent in rabbits and had been grown only in rabbits, was adapted to grow in Vero cells by the fusion of Vero cells with virus-infected rabbit spleen cells in the presence of polyethylene glycol, and subsequently passaged in Vero cells by co-culture technique. After several passages, free virus was produced at high titre. The Vero cell-adapted virus acquired the ability to infect several cell lines which were non-permissive to the unadapted virus. Analysis of virus proteins by immunofluorescence using monoclonal antibodies revealed that marked changes occurred in F, P, NP and M proteins by passage in Vero cells. In parallel to the adaptation to cell culture in vitro, the virulence of the virus measured in terms of clinical signs and histological lesions in the lymphoid tissues decreased in its severity whereas its immunosuppressive capacity was maintained unaltered. Thus, rinderpest virus with different degrees of virulence is now available for study in vitro.