Investigation of Diagnostic Parameters and Treatment Regimens for Tuberculosis in Bongo Antelope (Tragelaphus eurycerus)
The current status of the National Cooperative State-Federal Bovine Tuberculosis Eradication Program has significant implications for the zoo community. A 1997 U.S. Department of Agriculture report states that “the goal of eradication of bovine tuberculosis in the United States is biologically and economically feasible.” Further, the National Tuberculosis Program Review Team of the National Academy of Sciences (NAS) recommends that the “U.S. Department of Agriculture should vigorously pursue eradication of bovine tuberculosis in cattle, bison, elk, deer, and other farmed exotic hoofed species…and although improvements in tests used to detect infection appear possible and should be pursued, the committee believes existing diagnostic technology is adequate to support a vision of the total eradication of bovine tuberculosis from all domestic species, or any other species on farms unless it is introduced from another country.” The U.S. Department of Agriculture does, however, acknowledge that zoos and wildlife should be excluded from these definitions until we better understand how to manage and eliminate tuberculosis in these groups.1
It remains questionable whether existing technology is adequate to reliably diagnose tuberculosis antemortem in non-domestic hoofstock species. The lack of correlation between the “gold standard” intradermal test and actual disease has been well documented in a variety of exotic species and has often resulted in unnecessary euthanasia.2-5 While the test and slaughter method has proven effective in domestic species, it is neither desirable nor acceptable for endangered wildlife. Unfortunately, a lack of information on treatment combined with U.S. Department of Agriculture imposed restrictions often make euthanasia the only alternative.
Following the death of an adult male bongo antelope (Tragelaphus eurycerus) due to Mycobacterium bovis infection, an exposed herd of six female bongo was screened diagnostically five times over a 3-year period. Diagnostic evaluation included intradermal skin testing; thoracic radiography; cytology, culture, and Mycobacteria test direct (MTD) of tracheal wash samples; ELISA serology; and the blood tuberculosis test (BTB). Treatment was initiated with isoniazid (Major Pharmaceuticals, Chicago, IL, USA), rifabutin (Pharmacia-Upjohn Co., Kalamazoo, MI, USA), and ethambutol (Lederle Laboratories, American Cyanamid, Pearl River, NY, USA) in order to obtain pharmacokinetic information and evaluate the feasibility of treatment.
Immediately following the death of the male, five females (animals #1–5) were administered a single cervical test (0.1 ml Bovine PPD; U.S. Department of Agriculture, Animal and Plant Health Inspection Service). One young female (animal #6) was not tested due to its age. Four of the five animals tested had suspect reactions and one was negative. The same five animals were administered comparative cervical tests (CCT) 60 days later. Two animals were considered positive reactors (animals #1 and 2) and three were considered negative (animals #3, 4, 5). The CCT was administered 18 months post exposure to all six animals and four were considered reactors (animals #1–4), one was negative (animal #5), and the young, previously untested, female (animal #6) was suspect. Skin biopsies of the test sites were compatible with delayed hypersensitivity reactions in the four positive reactors. Animals #5 and #6 both died 6 months after the second CCT. Neither animal had histologic evidence of tuberculosis and M. bovis was not isolated by culture from either animal.
Mycobacterium bovis was not isolated from tracheal washes taken from the six bongo females (animals #1–6) submitted at 1-, 18-, 21-, and 23-months post-exposure although M. flavescens, M. kansasii, and a scotochromogenic were isolated from each of three samples. MTD results were negative on all six animals at 18 months post-exposure. Cytology of tracheal wash samples was not suggestive of mycobacterial infection (no evidence of foamy macrophages) in any of the samples.
Radiographs taken at 18-, 21-, and 23-months post-exposure showed no evidence of tuberculosis. ELISA serology using a five-antigen assay was evaluated at 18-, 21-, and 23-months post-exposure. One of the six animals was positive using a formula derived from known positive domestic bovids and all six were considered positive when evaluated using a formula derived from known positive cervids.
Twenty-six samples were submitted for BTB testing. Of those, one sample demonstrated evidence of M. bovis reactivity, four samples were negative (no reaction to either M. bovis or M. avium), and 21 of the samples were classified as “no data.” “No data” is reported when the assay controls do not perform to expected levels because of damaged cells or an absence of viable cells. This may be a result of stress to the animal, sedation effects, or cell damage during bleeding. In this study, BTB results differed between samples which were collected during narcotic immobilizations and samples collected during standing sedation. Of the 22 samples collected during narcotic immobilization, one sample showed M. bovis reactivity, one was negative and 20 were reported “no data.” Of four samples collected in a restraint chute under haloperidol (McNeil Pharmaceutical, Spring House, PA, USA) sedation, three were negative and one was reported “no data.”
Preliminary pharmacokinetic data indicates that blood levels of isoniazid approaching acceptable human levels can be achieved at a dose of 20 mg/kg orally. Rifabutin does not seem to be well absorbed at the doses given. Ethambutol results are unavailable at this time.
This project was supported in part by grants from the Institute of Museum and Library Services, The Conservation Endowment Fund of the American Zoo and Aquarium Association and Ortho-McNeil. The authors would like to thank Scott Larson and Dr. Mo Salman of Colorado State University for performing ELISA assays, Lederle labs for donating ethambutol and Pharmacia-Upjohn for donating rifabutin. A special thank-you is extended to the mammal and hoofstock staff at the Audubon Park Zoo for their care and behavioral conditioning of the bongo herd.
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3. Mann PC, Bush M, Janssen DL, Frank ES, Montali RJ. Clinicopathologic correlations of tuberculosis in large zoo mammals. J Am Vet Med Assoc. 1981;179(11):1123–1129.
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5. Wells SK, Sargent EL, Andrews ME, Anderson DE. Medical management of the orangutan. The Audubon Institute, New Orleans, LA. 1990.