Optimization of the Antigen 85 Immunoassay for Diagnosing Johne’s Disease in Elk (Cervus elaphus)
Abstract
Johne’s disease (JD) or paratuberculosis, caused by Mycobacterium avium ssp. paratuberculosis has previously been documented in a free-ranging herd of tule elk (Cervus elaphus nannodes) at the Point Reyes National Seashore. Due to the herd’s proximity to ongoing dairy operations, the risk to other free-ranging cervid populations, and the possible risk to humans, the National Parks Service, in collaboration with the California Department of Fish and Game, has been attempting to control this infection through proactive test-cull processes. Disease assessment in this wildlife population, however, has been hampered by diagnostic test methods that are oftentimes difficult or impossible to utilize and interpret in an antemortem fashion and the near-total lack of validation, optimization and standardization of the available test methods in the species of interest.
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 captive hoofstock species.2 In order to determine the applicability of this method for detecting JD in tule elk, optimization and validation of the immunoassay was attempted through analysis of serum from known infected and non-infected individuals and comparisons with other diagnostic methods. Preliminary results 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 paratuberculosis status in this species.
Literature Cited
1. Bentley-Hibbert, S.I., X. Quan, T.G. Newman, K. Huygen and H.P. Godfrey. 1999. Pathophysiology of antigen 85 in patients with active tuberculosis. Infect Immun. 67(2):581–8.
2. Mangold, B.J., R.A. Cook, M.R. Cranfield, K. Huygen, and H.P. Godfrey. 1999. Detection of elevated levels of circulating antigen 85 by dot immunobinding assay in captive wild animals with tuberculosis. J. Zoo Wildl. Med. 30(4):477–483.