Efficacy of ELISA compared to conventional tests (RBPT and CFT) for the diagnosis of Brucella melitensis infection in sheep.

An indirect ELISA (iELISA) using a B. abortus smooth lipopolysaccharide (S-LPS) as coating antigen and a polyclonal anti-sheep IgG peroxydase-labeled serum as conjugate was developed. The iELISA was assessed in comparison to the Food and Agriculture Organisation/International Atomic Energy Agency (FAO/IAEA) standard bovine ELISA kit (IAEA kit) using an anti-bovine IgG conjugate that cross-reacts with sheep antibodies, and with complement fixation test (CFT) and Rose Bengal Plate Test (RBPT). The evaluation was performed on sera from ewes experimentally infected with Brucella melitensis 53H38 (H38), using negative and positive sheep reference sera. No significant difference was found as regards to the specificity, the lower limit of detection and the estimated sensitivity of the two iELISAs. This suggests that an anti-bovine conjugate could allow the development of only one ELISA protocol for all ruminants. The iELISA, if well standardized, proved to be a good screening test able to be used either alone or in addition to RBPT.