EVALUATION OF ALLERGIC AND SEROLOGICAL TESTS FOR DIAGNOSING BRUCELLA-MELITENSIS INFECTION IN SHEEP

A total of 291 unvaccinated sheep from Brucella melitensis-infected fl ocks were examined for delayed-type hypersensitivity (DTH) responses w ith Brucellergene commercial allergen and with cold saline extract and cytosol from rough B. melitensis 115, and their sera were tested in t he rose bengal test (RBT), complement fixation test (CFT), and enzyme- linked immunosorbent assay (ELISA) with lipopolysaccharide. DTH reacti ons were maximal after 72 h, with no intensity differences among aller gens, inoculation sites (eyelid and tail), and doses tested. There wer e no differences in the results recorded by visual inspection and palp ation of inoculation sites, by measuring skin thickness with a caliper , or by microscopic examination of samples taken at necropsy; Six days after DTH testing, anergy was observed in 100% of the animals, and 10 0% reactivity was recovered only after 24 days. All animals were necro psied, and thorough bacteriological searches were performed. The sensi tivities found with the 140 animals from which B. melitensis was isola ted were ELISA, 100%; DTH, 97.1%; RBT, 92.1%; and CFT, 88.6%. Those re sults put into question the value of RBT and CFT as screening and conf irmatory tests for sheep brucellosis and at least indicate that their standardization should be modified. For 151 tested sheep from which B. melitensis was not isolated, the percentages of positive animals were ELISA, 100%; DTH, 94.0%; RBT, 57.6%; and CFT, 53.6%. All tests were n egative for 100 tested sheep from Brucella-free flocks. The different results of bacteriological and immunological tests suggest the usefuln ess of developing indirect tests able to distinguish truly infected an imals from those that have developed an immunological response.