Characterization of defective interfering (DI) particles of Pestedes petitsruminants vaccine virus Sungri/96 strain-implications in vaccine upscaling.

The present investigation deals with the characterization of defective interfering (DI) particles of Peste-des-petits ruminants (PPR) vaccine Sungri/96 strain generated as a result of high MOI in Vero cells. During the serial 10 passages, infectivity titres drastically reduced from 6.5 to 2.25 log10TCID50/ml at high MOI. Further, attenuation of CPE with high MOI indicated generation of DI particles that resulted in no/slow progression of CPE during the late passages. Monoclonal antibody based cell ELISA indicated normal protein (N & H) packaging in samples with DI activity. At genomic level, inconsistency in amplicon intensity of H gene was observed in RT-PCR, indicating a possible defect of H gene. Further analysis of copy number of PPRV by RT-qPCR indicated intermittent fluctuations of viral genomic RNA copies. The significant decline of viral RNA copies with MOI 3 (314 copies) compared to low MOI (512804 copies), proved that higher DI multiplicities cause more interference with the replication process of the standard virus. Therefore, MOI is critical for manufacturing of vaccines. These investigations will help in upscaling of PPR vaccines in view of ongoing National and Global PPR control and eradication programme.