Quantitative PCR: a quality control assay for estimation of viable virus content in live attenuated goat pox vaccine

Efficacy of live viral vaccine and vaccine-induced sero-conversion depends on the optimum number of live virus particles in a vaccine dose, which is one of the important aspects of quality control. In the present study, TaqMan probe quantitative polymerase chain reaction (QPCR) based on conserved DNA pol gene of capripoxvirus was developed for the quality control of attenuated monovalent goatpox and/or combined attenuated goatpox and peste des petits ruminants (PPR) vaccines. Cells infected with vaccine virus were harvested at critical time point and subjected to QPCR. A critical time point for harvest of Vero cells infected with various log10 dilutions of reference virus was determined to be 36 h (highest slope 3.062), by comparison of slopes of standard curves established with harvests at different time intervals. The assay method was evaluated using different batches of goatpox vaccine, and bivalent goatpox and PPR vaccine. The titers estimated by QPCR and TCID50 method were comparable to each other. The QPCR assay thus, could be used as an alternate method or supplementary tool for estimation of live GTPV particles in monovalent goatpox or bivalent goatpox and PPR vaccines.