Serum antigen 85 levels in adjunct testing for active mycobacterial infections in orangutans

Diagnosis of active mycobacterial disease in orangutans (Pongo pygmaeus) ha s been impeded by high levels of non-specific intradermal skin test reactiv ity to mycobacterial antigens. This may be due in part to cross reactivity between antigens, tuberculin concentrations used or other species-specific factors. Antigen 85 (Ag85) complex proteins are major secretory products of actively growing mycobacteria, and measurement of serum Ag85 could provide a method for determining active mycobacterial infections that was not depe ndent on host immunity. Serum Ag85 was measured by dot-immunobinding assay using monoclonal anti-Ag85, purified Ag85 standard and enhanced chemilumine scence technology in coded serum samples from 14 captive orangutans from a zoo in Colorado, 15 semi-captive orangutans in Malaysia, and 19 free-rangin g wild orangutans in Malaysia. Orangutans from Colorado (USA) were culture negative for Mycobacterium tuberculosis and M. avium, although all had labo ratory suspicion or evidence of mycobacterial infection; median serum Ag85 was 10 muU/ml (range, <0.25-630 <mu>U/ml). Of the semicaptive orangutans, s ix were skin test reactive and two were culture positive for M. avium on ne cropsy. Median serum Ag85 for this group was 1,880 muU/ml (0.75-7,000 muU/m l), significantly higher than that of Colorado zoo or free-ranging Malaysia n orangutans. Median serum Ag85 in the latter group was 125 muU/ml (range, 0.75-2,500 muU/ml). These data suggest that suggest that additional studies using more specific reagents and more samples from animals of known status are appropriate.