Detection of elevated levels of circulating antigen 85 by dot immunobinding assay ln captive wild animals with tuberculosis

Antemortem diagnosis of tuberculosis in captive wild animals is often diffi cult. In addition to the variability of host cellular immune response, whic h does not always indicate current active infection, reactivity to saprophy tic or other mycobacteria is common and may interfere with the interpretati on of the intradermal tuberculin skin test. Furthermore, the immobilization required for administering the test and evaluating skin reactions in these animals may result in unacceptable levels of morbidity and mortality, of p articular concern in individuals of rare or endangered species. Proteins of the antigen 85 (Ag85) complex are major secretory products of actively met abolizing mycobacteria in vitro. Production of these proteins by mycobacter ia during growth in vivo could result in increases in circulating levels of Ag85 in hosts with active tuberculosis. A dot blot immunoassay has been us ed to detect and quantify circulating Ag85 in captive wild animals with tub erculosis. Elevated levels of Ag85 were observed in animals with active tub erculosis as compared with uninfected animals. Study populations included a herd of nyala (Tragelaphus angasi) (n = 9) with no history of exposure to Mycobacterium bovis. Serum Ag85 levels ranged from (<5 to 15 mu U/ml (media n, 5 mu U/ml). The other group included 11 animals from a mixed collection with a documented history of an M. bovis outbreak. Animals with pulmonary g ranulomatous lesions (n = 3) had serum Ag85 levels ranging from 320 to 1,28 0 mu U/ml (median, 320 mu U/ml). Animals with only chronic mediastinal or m esenteric lymphadenitis (n = 4) had serum Ag85 levels ranging from <5 to 32 0 mu U/ml (median, 52.5 mu U/ml). Animals with no lesions present on necrop sy (n = 4) had serum Ag85 levels ranging from (5 to 80 mu U/ml (median, <5 mu U/ml). This assay could provide an important adjunct to intradermal skin testing for antemortem diagnosis of tuberculosis in nondomestic species.