Newcastle disease virus passage in MDBK cells as an aid in detection of a virulent subpopulation.

Newcastle disease virus strains (NDV) La Sota, Texas GB (GB), and mixtures of the two strains were serially passaged in embryonated chicken eggs or the MDBK cell line, a more restrictive culture system than eggs for NDV. The two culture systems were compared by evaluating culture harvests for pathogenicity in inoculated chickens; the harvests were identified by hemagglutination-inhibition tests against monoclonal antibodies that can differentiate La Sota and GB cultures. Both viruses, inoculated alone or as mixtures, were propagated by passage in chicken eggs. La Sota strain failed to propagate by continuous passage in MDBK cells, and only GB was identified in culture harvests propagated in MDBK cells that had been inoculated with GB or mixtures of GB and La Sota. The results indicate that the MDBK cell line is a more selective substrate than chicken eggs and suggest that passage in MDBK cells may aid in selecting for more virulent subpopulations of NDV in a mixed culture. Other reference NDV strains, pigeon NDV isolates, and recent lentogenic NDV isolates from chickens were also passaged in MDBK cells; all strains except those that are classified as lentogens like La Sota could be serially propagated in MDBK cells.