CHARACTERIZATION OF IVRI-CSF-BS CELL CULTURE ADAPTED VACCINE STRAIN FOR NEWCASTLE DISEASE VIRUS EXALTATION (END) AND CORRELATION OF VIRUS TITER BY END METHOD WITH FAT

The classical swine fever (CSF) viruses are generally non-cytopathic in nature and hence titrations of these viruses are mostly done by immunological methods such as fluorescent antibody technique (FAT). Although FAT is a gold standard and virus titration can be done very accurately, it involves tedious steps and demand skilful technological interventions. Exaltation of NDV (END method) has been used in the past to detect some of the CSF viruses in cell culture wherein Newcastle Disease Virus (NDV) readily proliferates in presence of CSFV and produces cytopathic changes. In the present study, a newly developed CSF vaccine virus strain (IVRI-CSF-BS) has been characterized for NDV exaltation and the virus has been found to be END+. This feature has been exploited for titration of the vaccine virus in PK-15 cells. The virus titre obtained by the END method has been correlated with the titres obtained by FAT and a linear correlation has been established as the titre obtained by END method was always 2 log10 lesser than the FAT titre.