Prevalence of cryptococcal antigenemia and nasal colonization in a free-ranging koala population

Laura J Schmertmann; Alex Kan; Valentina S A Mella; Cristina M Fernandez; Mathew S Crowther; George Madani; Richard Malik; Wieland Meyer; Mark B Krockenberger

doi:10.1093/mmy/myy144

Prevalence of cryptococcal antigenemia and nasal colonization in a free-ranging koala population

Med Mycol. 2019 Oct 1;57(7):848-857. doi: 10.1093/mmy/myy144.

Authors

Laura J Schmertmann^{1

2

3}, Alex Kan^{1

2

3}, Valentina S A Mella⁴, Cristina M Fernandez^{1

2

3}, Mathew S Crowther⁴, George Madani⁵, Richard Malik⁶, Wieland Meyer^{2

3

7}, Mark B Krockenberger^{1

7

8}

Affiliations

¹ Sydney School of Veterinary Science, The University of Sydney, Sydney, New South Wales, Australia.
² Molecular Mycology Research Laboratory, Centre for Infectious Diseases and Microbiology, Westmead Hospital, Faculty of Medicine and Health, Westmead Clinical School, The University of Sydney, Sydney, New South Wales, Australia.
³ The Westmead Institute for Medical Research, Westmead, New South Wales, Australia.
⁴ School of Life and Environmental Sciences, The University of Sydney, Sydney, New South Wales, Australia.
⁵ PO Box 3113, Hilltop, New South Wales 2575, Australia.
⁶ Centre for Veterinary Education, The University of Sydney, Sydney, New South Wales, Australia.
⁷ Marie Bashir Institute for Infectious Diseases and Biosecurity, The University of Sydney, Sydney, New South Wales, Australia.
⁸ Veterinary Pathology Diagnostic Services, B14, The University of Sydney, Sydney, New South Wales, Australia 2006.

PMID: 30649397
DOI: 10.1093/mmy/myy144

Abstract

Cryptococcosis, caused by environmental fungi in the Cryptococcus neoformans and Cryptococcus gattii species complexes, affects a variety of hosts, including koalas (Phascolarctos cinereus). Cryptococcal antigenemia and nasal colonization are well characterized in captive koalas, but free-ranging populations have not been studied systematically. Free-ranging koalas (181) from the Liverpool Plains region of New South Wales, Australia, were tested for cryptococcal antigenemia (lateral flow immunoassay) and nasal colonization (bird seed agar culture). Results were related to environmental and individual koala characteristics. Eucalypt trees (14) were also randomly tested for the presence of Cryptococcus spp. by bird seed agar culture. In sum, 5.5% (10/181) and 6.6% (12/181) of koalas were positive for antigenemia and nasal colonization, respectively, on at least one occasion. And 64.3% (9/14) of eucalypts were culture-positive for Cryptococcus spp. URA5 restriction fragment length polymorphism analysis identified most isolates as C. gattii VGI, while C. neoformans VNI was only found in one koala and one tree. Colonized koalas were significantly more likely to test positive for antigenemia. No associations between antigenemia or colonization, and external environmental characteristics (the relative abundance of Eucalyptus camaldulensis and season), or individual koala characteristics (body condition, sex, and age), could be established, suggesting that antigenemia and colonization are random outcomes of host-pathogen-environment interactions. The relationship between positive antigenemia status and a relatively high abundance of E. camaldulensis requires further investigation. This study characterizes cryptococcosis in a free-ranging koala population, expands the ecological niche of the C. gattii/C. neoformans species complexes and highlights free-ranging koalas as important sentinels for this disease.

Keywords: Cryptococcus; Phascolarctos cinereus; Liverpool Plains; animal sentinel; subclinical cryptococcosis.

MeSH terms

Animals
Animals, Wild / microbiology
Antigens, Fungal / blood*
Asymptomatic Infections / epidemiology*
Australia / epidemiology
Cryptococcosis / epidemiology
Cryptococcosis / veterinary*
Cryptococcus gattii / isolation & purification
Cryptococcus neoformans / isolation & purification
Ecosystem
Eucalyptus
Female
Male
Nose / microbiology*
Phascolarctidae / microbiology*
Prevalence

Substances

Antigens, Fungal