In mammals cryptococcal infections are caused by two species: Cryptococcus neoformans (var. grubii and var. neoformans) and C. gattii (formerly C. neoformans var. gattii or Cryptococcus bacillisporus). Infection is acquired mainly by inhalation from the environment5 with high inoculum levels of fungal particles being the key factor in the etiopathogenesis of the disease.1 In Australia there is a close relationship between C. gattii infections and the presence of certain species of eucalyptus, specifically Eucalyptus camaldulensis and E. tereticornis in the environment. Dead wood and decaying vegetation are also known to be an important substrate for Cryptococcus spp.2
Cryptococcosis is a significant infectious disease usually impacting upon koalas; the respiratory system being the main focus of disease. Local extension to the surrounding tissues can also occur in cryptococcal infections of the upper respiratory tract. Dissemination, especially to the central nervous system, can develop in the advanced stage of the disease.1
Increasingly the condition is being seen in other captive native Australian mammal species.5 Over a 10-year period at Taronga Zoo, cryptococcal infections have been reported in quokkas (Setonix brachyurus), koalas (Phascolarctos cinereus), red-necked wallabies (Macropus rufogriseus), yellow-bellied gliders (Petaurus australis), feather-tailed gliders (Acrobates pygmaeus), brush-tailed phascogales (Phascogale tapoatafa), greater stick-nest rats (Leporillus conditor), plains rats (Pseudomys australis) and an eastern barred bandicoot (Perameles gunnii). Affected animals suffered from a range of clinical conditions including sinusitis, pneumonia, pleuritis, and the disseminated form in three cases. The latter manifestation occurred more commonly in cryptic and nocturnal species housed indoors.
Diagnosis is based on the presence of clinical signs such as nasal discharge, facial asymmetry, weight loss, dyspnea, coughing, ataxia or seizuring and ancillary testing, namely cytology and the latex cryptococcal antigen agglutination test (LCAT). Cases of cryptococcosis are definitively diagnosed on the basis of (i) culture of Cryptococcus from a normally sterile site, (ii) demonstration of characteristic organism morphology in specimens submitted for cytology or histopathology, (iii) visualization and culture of Cryptococcus from nasal swabs plus a positive LCAT (titre ≥2) (to rule out nasal colonization) or (iv) a positive LCAT in an animal with characteristic signs.4
Recently a multimodal approach to therapy has been developed involving surgical debulking of lesions, and concomitant medical therapy using an oral triazole such as itraconazole or fluconazole in concert with amphotericin (M. Krockenberger, personal communication). In an attempt to limit possible spread to other organs during debulking, antifungal therapy is usually commenced prior to surgery. Regular testing of kidney and liver analytes, and LCAT levels should be performed to monitor the response to treatment and guard against possible side effects of therapy.
At Taronga Zoo animals housed in the nocturnal exhibit appeared to be particularly prone to cryptococcal infections. Control measures to decrease the incidence of Cryptococcus gattii in the environment include regular substrate changes and surface treatment of cage furniture with antifungal preparations. There is an ongoing need to examine initiatives to help decrease the environmental presence of C. gattii in animal enclosures through surface-acting environmental antifungal agents and the choice of appropriate substrates.3
The author thanks the staff of the Australian Registry of Wildlife Health and the Wildlife Hospital, Taronga Zoo, including Larry Vogelnest, Jane Hall, Karrie Rose, Richard Montali, Cathy Shilton, Jeanine Peters, Frances Hulst and Kimberly Vinette Herrin, for their assistance with this research and contributions to diagnosis and treatment of cases.
1. Krockenberger MB, Canfield PJ, Malik R. Cryptococcus neoformans var. gattii in the koala (Phascolarctos cinereus): a review of 43 cases of cryptococcosis. Med Mycol. 2003;41(3):225–234.
2. Krockenberger MB, Canfield PJ, Barnes J, Vogelnest L, Connolly J, Ley C, Malik R. Cryptococcus neoformans var. gattii in the koala (Phascolarctos cinereus): serological evidence for subclinical cryptococcosis. Med Mycol. 2002;40(3):273–282.
3. News. Vet team lead koala infectious diseases research. Aust Vet J. 2005;83(9):520.
4. O’Brien CR, Krockenberger MB, Wigney DI, Martin P, Malik R. Retrospective study of feline and canine cryptococcosis in Australia from 1981 to 2001: 195 cases. Med Mycol. 2004;42(5):449–460.
5. Vaughan RJ, Vitali SD, Eden PA, Payne KL, Warren KS, Forshaw D, Friend JA, Horwitz AM, Main C, Krockenberger MB and Malik R. Cryptococcosis in Gilbert’s and long-nosed potoroo. J Zoo Wild Med. 2007;38(4):567–573.