Problems associated with tuberculosis and brucellosis skin-test methods in northern Cameroon

Abstract

Eight hundred and ninety zebus from the north and far-north provinces of Cameroon were tested with two tuberculin assays to estimate the effect of infection by atypical mycobacteria on tuberculosis diagnosis in the region. Six hundred and seven of these animals were tested simultaneously against brucellosis with a delayed hypersensitivity test to brucellin (DHTB) and three standard serological assays as a comparison of the two classes of tests. The results demonstrated that only one quarter of the animals which were designated as tuberculous by the single tuberculin test were considered tuberculous by the comparative tuberculin test (CTT). For 34% of the CTT-reactive animals, borderline reactions were obtained and the results of the tests were uncertain. With regard to brucellosis, the relative sensitivity of the DHTB was 33%; the relative specificity was 96%. The limitation of the delayed hypersensitivity and serological methods are discussed. The most sensitive diagnostic procedure is a combination of both tests, where subjects are scored as positive if they are positive to either or both tests. The DHTB presents the advantage of requiring neither laboratory facilities nor animal identification.