zoonoses and communicable diseases common to ... - PAHO/WHO

ZOONOTIC TUBERCULOSIS 295and 101 animals from a tuberculosis-free area. Sensitivity of 73.6% and specificityof 94.1% were obtained (Ritacco et al., 1990). The authors note that ELISA wasable to detect IgG against M. bovis in the sera of cattle with active tuberculosis, butnot in those with a clinically inapparent infection (e.g., at the onset of infection orin the latent state). There was little coincidence between the results from the tuberculintest and results from ELISA. Antibodies were detected in almost three out offour bovines with active tuberculosis. In contrast to what happens with anergic animals,which lose cellular reactivity to the hypersensitivity test with tuberculin, antibodiesare more abundant when there is a strong antigenic discharge. Thus, ELISAcould be useful as a complement to the intradermal test in detecting anergic tuberculousanimals that represent a risk for the rest of the herd (Ritacco et al., 1990). Theresults obtained in humans infected by M. tuberculosis are not unlike those obtainedin cattle infected by M. bovis. Specificity was 93% in adults and 98% in children;sensitivity was 69% in adults and 51% in children. The conclusion is that enzymeimmunoassay can be useful for detecting patients with nonbacilliferous, extrapulmonary,and pediatric tuberculosis (de Kantor et al., 1991).The enzyme immunoassay can also be used to detect circulating antigens or todiagnose tuberculosis in homogenized animal tissues (Thoen et al., 1981). For a programto eliminate infected badgers, a serological procedure is being sought thatcould detect individual infected animals and thus prevent indiscriminate slaughter.In Australia, a simple test has been developed to measure in vitro the cell-mediatedimmune response to bovine PPD tuberculin. The test is based on detecting—using a sandwich enzyme immunoassay—gamma-interferon produced by incubation(for 24 hours) of whole bovine blood in the presence of tuberculin (Rothel etal., 1990). A field study conducted of a large number of cattle compared the analcaudaltest with PPD tuberculin and the gamma-interferon assay. Specificity withgamma-interferon was 96% to 98%, while sensitivity was 76.8% to 93.6% (dependingon the method of interpretation). If the two diagnostic tests are combined, it ispossible to obtain sensitivity of 95.2% (Wood et al., 1991; Wood et al., 1992). Thesandwich enzyme immunoassay to detect gamma-interferon in whole bovine bloodproved to be more sensitive and specific than the direct enzyme immunoassay fordetecting IgG in serum. In a study conducted in Argentina, the gamma-interferontest was positive in 9 of 19 animals that had tuberculous lesions limited to the lymphnodes and no antibodies in the ELISA test. In contrast, cattle with disseminatedlesions had a high antibody titer and little or no gamma-interferon production(Ritacco et al., 1991).Control: Prevention of human infection by M. bovis consists of the pasteurizationof milk, vaccination with BCG, and above all, control and eradication of bovinetuberculosis.The only rational approach to reducing and eliminating losses produced by theinfection in cattle and preventing human cases caused by M. bovis consists of establishinga control and eradication program for bovine tuberculosis. Eradication campaignsare usually carried out by administering tuberculin tests repeatedly, until allinfected animals are eliminated from the herd. Application of the tuberculin test andslaughter of reactors has given excellent results in all countries that have undertakeneradication campaigns. At present, many developed countries are free or practicallyfree of bovine tuberculosis. In developing countries, the inability of governments to