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The diagnosis of brucellosis in cattle and small ruminants requires the use of more than one serological test. The complement fixation test (CFT), the rose bengal test (RBT), and the serum agglutination test (SAT) are among the most useful tests for routine diagnosis. The microagglutination test (MAT) was developed as a simpler and more efficient test than the SAT. The relative efficacy of this test compared with that of the SAT was evaluated by using brucella-free sheep and goats prior to and after vaccination treatment. The specificities of the MAT and the SAT were 100%. Of the ewes and goats with a vaccination history, one ewe, expectedly a negative responder, had reactions in the MAT, the complement fixation test, and the rose bengal test but not in the SAT, suggesting a lower sensitivity of the SAT in this case. The calculated sensitivities of the MAT and the SAT were 93.9%. The agreement between MAT and SAT results for nonresponders was examined by using sera from unvaccinated lambs and kids (95.2% agreement), unvaccinated ewes and goats (84.4%), and ewes and goats with a vaccination history (43.9%). For the latter group higher levels of agglutination units were observed by the MAT than by the SAT in 51.5% of the samples. In testing sera from positive reactors after vaccination neither method was superior (MAT values were greater than SAT values for 23.5% of the samples, and MAT values were less than SAT values for 21.9% of the samples). Comparison of the methods on the individual sample level revealed a significant correlation between the MAT and the SAT (r ‫؍‬ 0.96 ؎ 0.005; P < 0.001). Since the MAT is simpler to perform than the SAT and can potentially be automated, the inclusion of the MAT as a supplementary test in brucellosis control programs is recommended.

During characterization by conventional biotyping tests of numerous Brucella melitensis isolates obtained in Israel in the last 2 years, we identified several strains of the biovar 1 serotype that are atypically susceptible to dyes and penicillin. Their coisolation from two brothers in a family that rears sheep and from the milk of one of their sheep and the prevalence of such strains in two distinct geographical zones in Israel provide epidemiological support for the notion that a new variant has been identified.

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