Heterologous resistance to superinfection by louping ill virus persistently infected cell cultures

Louping ill virus, a tick-borne arbovirus readily established a persistent infection in porcine kidney (PS) cells after initially inducing minor cytopathic changes. Nucleotide sequence analysis of the envelope glycoprotein of the viral RNA recovered from the persistently infected cells showed no changes as compared with the virus used to establish persistent infections. More than 80 per cent of the cells contained virus specific antigen when analysed by indirect immunofluorescence microscopy. This persistently infected cell line resisted superinfection with either homologous or most heterologous flaviviruses. However, the yellow fever French neurotropic virus (YF FNV) multiplied in the persistently infected cells and evidence of dual infections in these cells was obtained using specific monoclonal antibodies in double labelling immunofluorescence tests. The relevance of these observations is discussed in the light of other evidence that tick-borne viruses can survive for long periods in wild animal species.