The efficacy of the skin delayed-type hypersensitivity using a brucellin prepared from a mucoid strain of Brucella abortus to detect brucellosis

Eight-hundred-and-ninety-six cattle belonging to herds officially designated Brucella-free, and 190 cattle belonging to infected herds were tested with the skin delayed-type hypersensitivity (SDTH) test, using brucellin (273) prepared from a rnucoid strain of Brucella abortus. An increase in skinfold thickness ≥2mm was considered a positive SDTH test. The serum agglutination test, complement fixation test and bacteriological examination were used to confirm SDTH test results. Results show that 6 of the 896 uninfected cattle tested positive in the SDTH test, indicating a 99.3% specificity. Of the 44 cattle that tested serologically or bacteriologically positive, 33 tested positive in the SDTH test, indicating a 75% sensitivity. The value of the SDTH test was demonstrated by its ability to detect infection earlier than serological tests, and by confirming infection in cattle with ambiguous serological test results. An increase in skinfold thickness ≥1 mm in cattle in suspected herds should not be ignored, as it may indicate specific sensitization. We recommend the use of the SDTH test in combination with serological tests for early diagnosis of brucellosis in cattle

Serological response of cattle to Brucella allergen after repeated intradermal applications of this allergen

A study was conducted to determine whether an allergen that has been prepared from a mucoid strain of Brucella abortus triggers a serum antibody response that interferes with the interpretation of serologic tests results. Fifteen cattle seronegative for Brucella antigen were tested with the SDTH test several times. Blood samples were collected weekly and tested with the serum agglutination test and complement fixation test. Results show that some cattle tested seronegative after each of the SDTH tests while other cattle tested weakly positive with the serum agglutination test or the complement fixation test. All seropositive cattle tested seronegative 4–7 weeks after the last SDTH test indicating an antibody response of a transient nature. We conclude that serologic tests results indicating infection are reliable when recorded four weeks after a single SDTH test. If cattle are tested with the SDTH test several times an interval of seven weeks should be observed after the last test to ensure a reliable interpretation of the serologic tests results