EFFICACY OF DIFFERENT ROSE-BENGAL AND COMPLEMENT-FIXATION ANTIGENS FOR THE DIAGNOSIS OF BRUCELLA-MELITENSIS INFECTION IN SHEEP AND GOATS

Fifteen different Rose Bengal antigens showed large differences with r espect to pH, cell concentration and agglutination with the internatio nal standard anti-Brucella abortus serum, demonstrating the lack of in ternational standardisation. Their sensitivity and specificity, compar ed with that of the complement fixation test, were evaluated for the d iagnosis of B melitensis infection in culture-positive sheep, brucella -free ewes, and sheep and goats belonging to field flocks under differ ent epidemiological conditions. All the Rose Bengal antigens and the c omplement fixation test had 100 per cent specificity when testing bruc ella-free sheep or animals belonging to flocks in unvaccinated brucell osis-free areas, but there mere large differences in sensitivity betwe en the Rose Bengal antigens with sera from culture-positive sheep or f rom animals belonging to infected flocks. When using the most sensitiv e antigen, no difference was observed in Rose Bengal sensitivity betwe en animals infected with either biovar 1 or biovar 3 of B melitensis. The relationship between the sensitivity of the Rose Bengal antigens a nd cell concentration was unclear, but their sensitivity was related t o the standardisation of the antigens with the international standard serum. The complement fixation test was less sensitive than the Rose B engal test when testing culture-positive sheep. When testing sera from animals belonging to infected flocks with antigens standardised accor ding to European Union rules, no great differences were observed in th e sensitivities of the two tests. However, great differences in sensit ivity between the Rose Bengal antigens were observed with sera from an imals belonging to flocks with low levels of prevalence, Moreover, the numbers of animals positive in both tests decreased, and the numbers of animals positive in only one of the tests increased, as the prevale nce decreased.