Study of the Antibody Response against Mycobacterium tuberculosis Antigens in Warao Amerindian Children in Venezuela

Abstract

This study was aimed at investigating alternate methods for serodiagnosis of tuberculosis (TB), which are needed because bacteriologic diagnosis of childhood TB is difficult. A selection of 80 serum and saliva samples were tésted from Warao indigenous children under 15 years of age; 34 high TB suspects (28 positive and 6 negative for the tuberculin skin test, TST) and 46 healthy Contact children (32 positive and 14 hégative for the TST). Several enzyme-rinked immunosorbent assay (ELISA) serological tests were developed to test for Mycobacterium tuberculosis- specific antibodies, including serum IgA, IgG; IgE, and secretory IgA (sIgA) in saliva against 3 specific antigens (PPD, HSP60, 38 kDa). Of these, 2 antigens, P.PD and 38 kDa, showed significantly higher reactivity. The sensitivity and specificity of these tests for diagnosis remained limited, between 26.5% and 38.2%, and 77.4% and 97%, respectively. Of all the samples studied and combinations realized between all isotypes and antigens combined with 3 isotypes (anti-PPD IgG; IgE, and anti-38kDa sIgA) man{lged to detect the largest number of patients, showing an improved sehsitivity level of 64.7%, although specificity levels dropped to 81.8%. These results were compared with the Omega diagnostics commercial kit results. The commercial kits showed significantly lower reactivity (sensitivity of20% and 13.33% to Myco G dnd Complex Plus, respectively) anda specificity óf 100%. This study shows that in indigenous populations of Ve1'Íezuelaw, here invasive procedures cannot be used to select samples but evaluation with a chest X-ray for radiological studies is ávailab!e, the combination of 3 specific isotypes may be a useful tool to increase diagnostic accurac)1 with pulmonary TB in this population, when used together with clinical and epidemiologic(ll criteria.