Summary
A study was conducted to determine possible nonspecific skin delyed‐type hypersensitivity (SDTH) test reactions in cattle tested with a Brucella allergen.
Cattle (n = 14) experimentally inoculated with microorganisms known serologically to crossreact 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 ≥ 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 ≥ 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.
Summary
Individual milk samples and artificially constructed tank milk samples from cows with naturally occurring brucellosis were examined by the enzyme‐linked immunosorbent assay (ELISA) using sonicated B. abortus S‐99 antigen, and mouse monoclonal anti‐bovine IgM, IgA, and IgG1 conjugates. ELISA results were compared with the results of the milk ring test using either 1 ml milk (MRT‐1) or 8 ml milk (MRT‐8).
The ELISA using mouse monoclonal anti‐bovine IgG1 conjugate was sensitive and specific. In testing individual milk samples and constructed tank milk samples containing milk with low titers in the MRT‐1 the ELISA was superior to the MRT‐1, and MRT‐8. In testing other milk samples, the ELISA was as sensitive or slightly less sensitive than the MRT‐8. From a total of 5,910 milk samples collected from cows free from brucellosis, only 24 (0.4 %) samples tested positive in the ELISA. All 500 tank milk samples collected from farms negative for brucellosis tested negative in the ELISA.
We concluded that the ELISA is a good substitute for the MRT‐1 to detect antibodies against Brucella in milk from individual cows. When tank milk is tested for antibodies against Brucella, however, both the MRT‐8 and the ELISA should be used.
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