Further Optimization and Validation of the Antigen 85 Immunoassay for Diagnosing Mycobacteriosis in Wildlife
1Wildlife Health Center, School of Veterinary Medicine, University of California, Davis, CA, USA; 1Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis, CA, USA; 3Tulane Regional Primate Center, Covington, LA, USA; 4Wildlife Conservation Society, New York Zoological Society, Bronx, NY, USA; 5Department of Pathology, New York Medical College, Valhalla, NY, USA
Mycobacteriosis caused by Mycobacterium bovis, M. tuberculosis, and M. avium has been a well-documented health problem for zoological collections since the late 19th century. Prevalence estimation in these captive wildlife populations has been hampered by diagnostic test methods that are often difficult or impossible to conduct and/or interpret due to the requirement for multiple immobilizations for measurement of response, the occurrence of nonspecific results with methods such as the intradermal skin test, and/or the near-total lack of validation, optimization, and standardization of any of the available test methods in the species of interest. Additionally, because intradermal skin testing is the primary screening method for many of these species, the ability to compare exposure in captive wildlife to exposure in free-ranging populations has been limited due to the difficulty with follow-up in free-ranging populations. Lastly, unlike testing methods that use serologic techniques, skin testing precludes retrospective studies of banked samples to determine onset of reactivity.
Recently, researchers working with tuberculosis in humans have developed an immunoassay that detects a serum protein complex (the antigen 85, or Ag85, complex) produced by mycobacteria in the early stages of mycobacterial infections.1 Previous work has shown that this method is a promising diagnostic tool in the evaluation of tuberculosis exposure in some primates, including orangutans (Pongo pygmaeus), a species known for nonspecific tuberculin responses,2 and captive hoofstock species.3 In order to determine the feasibility and applicability of this method for captive and free-ranging wildlife species, we have undertaken a number of pilot studies on different populations of interest with the goal of optimizing and validating the immunoassay through analysis of serum from known infected and noninfected individuals, and through comparisons with other diagnostic methods. Thus far, we have begun evaluating the applicability of the Ag 85 immunoassay in various avian, primate, rhinoceros, and hoofstock species for detecting mycobacteriosis, including paratuberculosis. Preliminary results, a summary of which will be presented, indicate that this method may be a valuable adjunct to other testing methods (including gamma interferon and multiple-antigen ELISA) to allow a better evaluation of true mycobacterial status in these species.
1. Bentley-Hibbert SI, Quan X, Newman TG, Huygen K, Godfrey HP. Pathophysiology of Antigen 85 in patients with active tuberculosis. Infect Immun. 1999;67(2):581–588.
2. Kilbourn AM, Godfrey HP, Cook RA, Calle PP, Bosi EJ, Bentley-Hibbert SI, K. et al. Serum Antigen 85 levels in adjunct testing for active mycobacterial infections in orangutans. J Wildl Dis. 2001;37(1):65–71.
3. Mangold BJ, Cook RA, Cranfield MR, Huygen K, Godfrey HP. Detection of elevated levels of circulating antigen 85 by dot immunobinding assay in captive wild animals with tuberculosis. J Zoo Wildl Med. 1999;30(4):477–483.