Diagnostic evaluation of serological assays and different gene based PCR for detection of Brucella melitensis in goat

Accurate diagnostic tests for brucellosis of small ruminants are necessary for control of Brucella melitensis, the most frequent cause of human brucellosis in India. In present study we attempted to evaluate the serological tests vis-a-vis PCR for diagnosis of caprine brucellosis. Commonly used different serological test (viz.; recombinant Omp31 based ELISA (rELISA), dot-ELISA, B. melitensis whole antigen based ELISA (pELISA), SAT, CFT, RBPT and AGPT) were employed for diagnosis of brucellosis in 138 abattoir bound animals having history of abortion. Same animals were subjected to tissue PCR based on 07 different commonly used target genes (viz.; 16s rRNA, 16s-23s rRNA, BCSP-31, L7/L12, Omp2b, Omp31 and BP26) for detection of B. melitensis in goats. Diagnostic efficiencies and logistic analysis of serological assays indicated that rELISA and dot-ELISA combination is the best for detection of anti B. melitensis antibodies in goats. On the other hand, diagnostic efficiencies and logistic analysis of different gene based PCR revealed that for genus based identification of Brucella organism 16s rRNA and 16s-23 rRNA gene is the best target while for species based identification Omp31 and BP26 gene targets are the suitable. Study was also performed on the possible combination and logistic regressions of different gene based PCR and serological assays which shown the maximum probability of 16SrRNA and 16S-23SrRNA gene based PCR and rELISA and Dot-ELISA for serological assays. The sensitivity and specificity of serological and PCR-based methods used was also determined. It was concluded that, in goats, the sensitivity and specificity of most serological and PCR-based methods are not well established and their real value for use with clinical samples and hence diagnosis has not been validated. There is still a great deal of work required for verification, validation, establishment of standards before we establish accurate diagnosis of brucellosis in goats.