Automated particle-counting immunoassay of anti-brucella antibodies: a comparative study with: ELISA, SAT, CFT, RBPT and AGT

Antibodies to B. abortus were titrated in bovine sera by particle-counting immunoassay, using lipopolysaccharide-coated latex. Rheumatoid factor was used to amplify the weak agglutinating activity of IgG antibodies. Specificity was achieved by neutralisation of cross-reacting antibodies either by reduction of IgM antibodies with dithiothreitol or by absorption with E. coli 0157 extracts. No false positive results were observed with PACIA in heifers which had been infected with S. urbana whereas classical tests and ELISA gave false positive results in 2 and 1 respectively of the 4 infected animals. With E. coli absorption PACIA detected all classes of antibodies and revealed antibodies in all infected animals, before all classical tests and before ELISA in 45 per cent of the heifers, on the same time as ELISA in 45 per cent, and after ELISA in 10 per cent