Abstract
Cryptococcosis is typically a sporadic disease that affects a broad range of animal species globally. Disease is a consequence of infection with members of the Cryptococcus neoformans or Cryptococcus gattii species complexes. Although cryptococcosis in many domestic animals has been relatively well-characterized, free-living wildlife animal species are often neglected in the literature outside of occasional case reports. This review summarizes the clinical presentation, pathological findings and potential underlying causes of cryptococcosis in various other animals, including terrestrial wildlife species and marine mammals. The evaluation of the available literature supports the hypothesis that anatomy (particularly of the respiratory tract), behavior and environmental exposures of animals play vital roles in the outcome of host–pathogen–environment interactions resulting in different clinical scenarios. Key examples range from koalas, which exhibit primarily C. gattii species complex disease presumably due to their behavior and environmental exposure to eucalypts, to cetaceans, which show predominantly pulmonary lesions due to their unique respiratory anatomy. Understanding the factors at play in each clinical scenario is a powerful investigative tool, as wildlife species may act as disease sentinels.
Highlights
Cryptococcosis in wildlife and domesticated ungulates has been well reported but has not been systematically reviewed
The consensus view is that any association of cryptococcosis caused by C. neoformans with reduced immune status is weak [29], there is some suggestion of an impact of retroviral status and genomic predispositions on disease outcomes in cats, with an increased likelihood of severe cryptococcosis in cats infected by feline leukemia virus and/or feline immunodeficiency virus [30] and higher prevalence and more severe and refractory disease in Ragdoll and Birman breeds
In most of Australia, especially along the east coast, cryptococcosis is usually caused by C. gattii VGI, in south-western Western Australia (WA) infections can involve C. gattii VGII, including cases where koalas have been infected in WA and developed disease following translocation elsewhere within Australia [78]
Summary
Cryptococcosis in wildlife and domesticated ungulates has been well reported but has not been systematically reviewed. The fragmentary nature of the existing literature ranges from single case reports due to opportunistic necropsy examinations after accidental death, to more detailed case studies of patients living in artificial captive environments (e.g., koalas in captivity in Australia, USA, Spain and Japan) or involved in outbreak events (e.g., in Vancouver Island and nearby British Columbia; epizootics affecting goats in Spain) Complicating this fragmented literature, the accuracy of pathogen identification is influenced by which diagnostic specimens were collected and by the variable application of available laboratory tools (i.e., cytology, histopathology, culture, MALDI-TOF MS, multilocus sequence typing (MLST) and whole-genome sequencing), and by taxonomic reassessment of the pathogens over time. We have included reports concerning animals living in undomesticated settings (i.e., wild animals) in their natural environment, animals living in a confined area such as zoological parks (e.g., koalas, marine mammals, large felids) and, briefly, ungulates living in an open range environment
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