Specificity of the skin delayed-type hypersensitivity test in brucellosis free cattle tested with a Brucella allergen

A study was conducted to determine possible nonspecific skin delayed-type hypersensitivity (SDTH) test reactions in cattle tested with a Brucella allergen. Cattle (n = 14) experimentally inoculated with microorganisms known serologically to cross-react with Brucella and cattle (n = 549) from Brucella free herds were tested serologically and with the SDTH test. The increase in skinfold thickness at the injection site of the allergen was measured to the nearest mm with calipers 48 hours after injection. The results show that none of the SDTH test reactions in cattle experimentally inoculated with microorganisms other than Brucella exceeded 2.0 mm. This indicates that an increase in skinfold thickness > or = 2.0 mm can be considered a positive SDTH test reaction. When this norm was applied to cattle in Brucella free herds 11/549 (2%) cattle showed an increase > or = 2.0. It is concluded that infections with microorganisms other than Brucella are unlikely to cause sensitization that interferes with the SDTH test when used to detect brucellosis. Therefore, the SDTH test can be used to verify positive serologic tests results that might have been caused by microorganisms that serologically cross-react with Brucella.