Evaluation of orf virus (ORFV) isolation in continuous lamb testis cells (OA3.Ts) and development of a co-culture method with infected cells to increase infectivity

Continuous foetal lamb testis cells OA3. Ts was used to compare the isolation of a vaccine orf virus (ORFV) strain that had been adapted to primary lamb testes cells, with scab derived wild-type/field ORFV isolates. The wild type virus showed an accelerated and exaggerated cyto-pathic effect (CPE) than the vaccine virus as has been demonstrated by immunofluorescent detection of viral antigen using ORFV monoclonal antibodies. ORFV could be successfully isolated in OA3. Ts foetal lamb testes cells and can be used for direct isolation of the virus from clinical samples. Two different methods of cell culture infection were also compared during sub-culture, one using infected supernatant as the inoculum and the other using infected cells as a modified method for infecting healthy culture cells. The present study also indicates that a higher infection can probably be achieved with inoculating infected cells together with healthy ones as a co-culture method during propagation of ORFV. This has been revealed as visibly pronounced CPE and presence of larger and multiple aggregates of cytoplasmic inclusions than cells infected with infected supernatant alone.