DEVELOPMENT OF A COMPETITIVE ELISA FOR DETECTING ANTIBODIES TO THE PESTE DES PETITS RUMINANTS VIRUS USING A RECOMBINANT NUCLEOPROTEIN

A competitive ELISA based on the reaction between a monoclonal antibod y (mAb) and a recombinant nucleoprotein of the peste des petits rumina nts virus (PPRV) was developed. This protein was obtained in large qua ntities from insect cells infected with a PPR nucleoprotein recombinan t baculovirus (N-B). The competitive ELISA was compared with the virus neutralisation test (VNT) for detecting specific antibodies to PPRV i n sheep and goats. The time consuming VNT is the only prescribed test that is capable of distinguishing between PPRV and the cross-reactive rinderpest virus (RPV). The competitive ELISA involves the simultaneou s addition of the mAb and antibodies present in a positive serum, lead ing to competition for a specific epitope on the N-B. Optimum conditio ns were obtained by using serum samples which had positive or negative neutralising activity against PPRV or RPV. A negative cut-off point w as determined on PPRV-negative sera from RPV-vaccinated cattle. A thre shold value of 48 per cent inhibition, calculated from the mean for th is population plus 2.7 standard deviations, was used in routine testin g. A total of 683 sera were analysed by the competitive ELISA and the VNT. A good correlation (r = 0.94) was observed between the titres obt ained in the two tests, with 80 sera that were from laboratory sources . The agreement between the two tests was determined on 271 field sera (kappa = 0.825). Their relative sensitivity (94.5 per cent) and speci ficity (99.4 per cent) were assessed on the 148 laboratory sera plus t he 271 sera used for the determination of kappa. The durations of pass ive immunity in 23 goats, as determined by the VNT and the competitive ELISA, were 120 and 90 days, respectively, which indicates some diffe rences between the anti-haemagglutinin and anti-N protein kinetics. Th e competitive ELISA is as sensitive and specific as the VNT, with the added advantage that it uses an antigen that is safe and can be produc ed in large quantities.