Four adult red-necked wallabies (Macropus rufogriseus) within a collection of 24 adults in the Blank Park Zoo were identified with granulomas or abscesses containing acid-fast organisms in 2012. The animals were diagnosed late in the course of disease,1 with lesions greater than 6 cm detected by digital radiography or palpation. Mycobacterium avium, subsp. hominissuis and Mycobacterium intracellulare were identified by mycobacterial culture and genotyping by the National Veterinary Services Laboratory. M. avium subsp. hominissuis and M. intracellulare are ubiquitous in the environment. M. avium subsp. hominissuis is commonly isolated from non-tuberculous infections in humans and swine.2 Antemortem diagnostic tools for the detection of mycobacterial infections in macropods are largely unavailable. Intradermal tuberculin testing produces inconsistent results and is therefore of limited diagnostic value.3 Radiography is useful for localizing the site of infection in cases where osteomyelitis or calcified lymph nodes are present.4
In 2013, a health screening protocol for the red-necked wallaby population within the zoo was created which includes computed tomography (CT), in addition to physical exam, serology, hematology, and digital radiography to identify animals that may have subclinical illness. The results of this study have identified the normal and abnormal CT anatomy of wallabies, assisted in the identification and treatment of health conditions, and assessed the prevalence of wallaby retrovirus6,7 in the evaluated animals. Skull and body CT scans identified abnormalities (dental, cardiac) which modified management of these individual animals, but no lesions suggesting subclinical mycobacteriosis have been observed.
1. Durham, P., J. Finnie, D. Lawrence, and P. Alexander. 1996. Blindness in south Australian kangaroos. Aust. Vet. J. 73:111.
2. Thegerstrom, J., B. Jonsson, L. Brudin, B. Olsen, A.E. Wold, J. Emerud, and V. Friman. 2012. Mycobacterium avium subsp. avium and subsp. hominissuis give different cytokine responses after in vitro stimulation of human blood mononuclear cells. PLoS ONE. 7(f):e34391, doi:101371/journal.pone.0034391.
3. Buddle, B.M., and L.J. Young. 2000. Immunobiology of mycobacterial infections in marsupials. Dev. Comp. Immunol. 24: 517–529.
4. Vogelnest, L., and T. Portas. 2008. In: Vogelnest, L., and R. Woods (eds). Medicine of Australian Mammals. CSIRO Publishing, Collingwood, Australia. 185–186
5. Story, A., R.W. Aldridge, I. Abubakar, H.R. Stagg, M. Lipman, J.M. Watson, and A.C. Hayward. 2012. Active case finding for pulmonary tuberculosis using mobile digital chest radiography: an observational study. Int. J. Tuberc. Lung. Dis. 16: 1461–1467.
6. Kapustin, N., C. Kanitz, and T. Muencht. 1999. Identification of a retrovirus in Bennett’s (Macropus rufogriseus frutica) and Dama (Tammar) (Macropus eugenii) wallabies. Proc. Am. Assoc. Zoo Vet. 261–262.
7. Georoff, T.A., P.H. Joyner, J.P. Hoover, M.E. Payton, and R.M. Pogranichniy. 2008. Seroprevalence of retrovirus in North American captive macropodidae. J. Zoo Wildl. Med. 39:335–341.