Retrospective Evaluation of Mycobacteriosis in the Houston Toad (Anaxyrus houstonensis): Clinical Presentations, Pathologic Findings, and Prevention
American Association of Zoo Veterinarians Conference 2017
Gregory Walth1; Eric Snook2, DVM, PhD; Lauren Howard3, DVM, DACZM
1College of Veterinary Medicine, Iowa State University, Ames, IA, USA; 2Texas A&M Veterinary Medical Diagnostic Laboratory, College Station, TX, USA; 3San Diego Zoo Safari Park, Escondido, CA, USA


The Houston toad (Anaxyrus houstonensis) is an endangered amphibian native to east-central Texas, USA.2 The Houston Zoo maintains a colony of the species for captive assurance and breeding. Mycobacterial disease has been a significant cause of morbidity and mortality over the past 7 yr. A retrospective study of mycobacteria cases from January 2009 through July 2016 was conducted to characterize the most common findings on clinical presentation, the success of antemortem diagnostics, and the most common pathologic findings. One hundred ninety-nine cases were identified. The most common presentations were abnormal posturing or ambulation, joint or toe swelling, and cutaneous swelling, ulcer, or erythema. Histopathology showed that the musculoskeletal and visceral body systems were most commonly affected, with granulomatous osteomyelitis and granulomatous pneumonia most common, respectively. Of the cases that had both cytology and histopathology performed, 67% of cases were positive on both tests, suggesting that cytology is a moderately good antemortem test for mycobacterial disease, but has limitations. Several cases that were positive for acid-fast bacilli on cytology failed to demonstrate these organisms on histopathology. This may be due to the strong acids used in the tissue decalcification process,1 and alternative methods of tissue preparation are recommended if trying to detect mycobacterial species.


The authors would like to thank the Houston toad keepers and the technical staff at the Houston Zoo for their hard work and relentless dedication to this project.

Literature Cited

1.  Anderson G, Coup AJ. Effect of decalcifying agents on the staining of Mycobacterium tuberculosis. J Clin Pathol. 1975;28:744–745.

2.  Duarte A, Brown DJ, Forstner MRJ. Documenting extinction in real time: decline of the Houston toad on a primary recovery site. J Fish Wildl Manag. 2014;5:363-371.


Speaker Information
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Gregory Walth
College of Veterinary Medicine
Iowa State University
Ames, IA, USA

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