Specificity of the Skin Delayed‐Type Hypersensitivity Test in Brucellosis Free Cattle Tested with a Brucella Allergen

Abstract

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.

Diagnosis of bovine brucellosis by skin test: conditions for the test and evaluation of its performance

“…However, for some doubtful cases and in order to quantify the reaction, the thickening of the skin should be measured with a spring meter. Although a cut‐off of 2 mm is legally prescribed for the tuberculosis skin test and has been proposed for a brucellosis skin test (Bercovich and others 1993), this value is not suitable for the skin test with brucellin which has a very low sensitivity at this level, ranging from about 85 per cent one month after experimental infection, to 52 per cent after six months (Table 3).…”

Diagnosis of Brucellosis

“…While skin testing has certain logistical drawbacks, the test, in combination with serological tests can provide part of a sensitive and specific protocol for detection of infected animals, especially latently infected animals devoid of measurable antibody. It was shown to be able to eliminate most false positive serological reactors [233,234], however, in a relatively recent review [235], both B. abortus vaccinated animals and animals infected with cross reacting microorganisms gave skin tests reactions for a period of time.…”

The use of skin delayed‐type hypersensitivity as an adjunct test to diagnose brucellosis in cattle: A review

“…The evaluation of the specificity and the sensitivity of the test was also difficult due to the different criteria set by the various workers to indicate brucellosis (37,44,87). Nonetheless, the SDTH test is highly specific (17,31,62,76), it detects brucellosis in seronegative cattle (16), and it confirms brucellosis in cattle with ambiguous serological test results (13,15). Hence, it is appropriate to assess the diagnostic ability of a combination of serological tests and the SDTH test.…”

“…c. brucellins prepared from smooth or mucoid strains of Brucella are better suited for use in the field than brucellins prepared from rough strains (19). d. it is possible that some cattle may elude detection with the SDTH test, because not all infected cattle are optimally sensitized at the time of testing (15,17). For economical reasons, brucellin 273 was chosen for further study of the reliability of the SDTH test to detect brucellosis.…”