An evaluation of the comparative tuberculin skin test for detecting tuberculosis in farmed deer

A comparative cervical skin test using 1.0 mg/ml bovine purified protein derivative and 0.5 mg/ml avian purified protein derivative was evaluated as a method for detecting tuberculosis in farmed deer. A positive comparative cervical skin test reaction was defined as a bovine response with a 2 mm or greater increase in skin thickness which was greater or equal to the avian response. Estimates of the sensitivity of the comparative cervical skin test were obtained from a series of experiments conducted on 60 deer intratracheally inoculated with Mycobacterium bovis. Prior tuberculin skin testing was found to suppress the skin reactivity to a subsequent comparative cervical skin test. This effect was most pronounced at short intervals of 3-7 days, but could still be measured 60 days after the previous test. When the test interval was greater than 60 days, the sensitivity of the comparative cervical skin test was 91.4%. The specificity of the comparative cervical skin test was 98.7% when 1157 deer from 17 uninfected herds with a history of nonspecific skin test reactions were examined. There was no statistical difference in the mean skin thickness increases of three groups of infected animals tested with 2 mg/ml, 0.2 mg/ml and 0.02 mg/ml of bovine purified protein derivative respectively.