Cryptococcus neoformans var. gattii in the koala (Phascolarctos cinereus): serological evidence for subclinical cryptococcosis

Cryptococcus neoformans rapidly invades the murine brain by sequential breaching of airway and endothelial tissues barriers, followed by engulfment by microglia

Cryptococcus neoformans causes lethal meningitis and accounts for approximately 10%-15% of AIDS-associated deaths worldwide. There are major gaps in our understanding of how this fungus invades the mammalian brain. To investigate the dynamics of C. neoformans tissue invasion, we mapped fungal localization and host cell interactions in infected brain, lung, and upper airways using mouse models of systemic and airway infection. To enable this, we developed an in situ imaging pipeline capable of measuring large volumes of tissue while preserving anatomical and cellular information by combining thick tissue sections, tissue clarification, and confocal imaging. We confirm high fungal burden in mouse upper airway after nasal inoculation. Yeast in turbinates were frequently titan cells, with faster kinetics than reported in mouse lungs. Importantly, we observed one instance of fungal cells enmeshed in lamina propria of the upper airways, suggesting penetration of airway mucosa as a possible route of tissue invasion and dissemination to the bloodstream. We extend previous literature positing bloodstream dissemination of C. neoformans, by finding viable fungi in the bloodstream of mice a few days after intranasal infection. As early as 24 h post systemic infection, the majority of C. neoformans cells traversed the blood-brain barrier, and were engulfed or in close proximity to microglia. Our work presents a new method for investigating microbial invasion, establishes that C. neoformans can breach multiple tissue barriers within the first days of infection, and demonstrates microglia as the first cells responding to C. neoformans invasion of the brain.IMPORTANCECryptococcal meningitis causes 10%-15% of AIDS-associated deaths globally. Still, brain-specific immunity to cryptococci is a conundrum. By employing innovative imaging, this study reveals what occurs during the first days of infection in brain and in airways. We found that titan cells predominate in upper airways and that cryptococci breach the upper airway mucosa, which implies that, at least in mice, the upper airways are a site for fungal dissemination. This would signify that mucosal immunity of the upper airway needs to be better understood. Importantly, we also show that microglia, the brain-resident macrophages, are the first responders to infection, and microglia clusters are formed surrounding cryptococci. This study opens the field to detailed molecular investigations on airway immune response, how fungus traverses the blood-brain barrier, how microglia respond to infection, and ultimately how microglia monitor the blood-brain barrier to preserve brain function.

Molecular epidemiological investigation of Cryptococcus spp. carried by captive koalas (Phascolarctos cinereus) in Japan

Cryptococcus neoformans and Cryptococcus gattii cause cryptococcosis, a systemic mycosis that infects a wide range of species. Recent molecular biological investigations have allowed for the genotyping of these species, providing more detailed information on their pathogenicity and infection routes. Koalas (Phascolarctos cinereus) are frequently colonized by Cryptococcus spp., but molecular epidemiological studies have yet to be conducted in Japan. Here, we conducted multi-locus sequence typing (MLST) analysis on Cryptococcus spp. colonization isolates obtained from all koalas kept in seven parks across Japan. Out of 46 koalas examined, 10 (22%) were positive for C. gattii and 3 (6.5%) were positive for C. neoformans. All C. gattii isolates belonged to molecular type VGI and were either sequence type (ST) 51 or a novel ST, and all C. neoformans isolates belonged to molecular type VNI and ST23. Despite the frequent movement of koalas between parks, the STs were relatively park-specific, suggesting that the floor of the rearing barns is a source of infection and may act as a reservoir. MLST analysis confirmed that C. gattii was transported, established, and spread by koalas in areas where C. gattii was not originally present. MLST analysis is considered useful in assessing the pathogenicity and tracing the transmission routes of Cryptococcus spp. carried by koalas.IMPORTANCEThis is the first study to conduct a multi-locus sequence typing analysis on Cryptococcus spp. carried by captive koalas in Japan. Cryptococcosis remains a globally high-fatality fungal infection in humans, and captive koalas are known to carry a high percentage of Cryptococcus spp. Through this research, the molecular types and transmission routes of Cryptococcus spp. carried by koalas have been elucidated, revealing the potential role of enclosure flooring as a reservoir. It has been confirmed that Cryptococcus gattii, which is not endemic in Japan, has become established through koalas and is spreading to new individuals in Japan. This study is believed to provide valuable insights into koala conservation and contribute to the One Health approach for Cryptococcosis, a zoonotic infection.

Cryptococcus neoformans rapidly invades the murine brain by sequential breaching of airway and endothelial tissues barriers, followed by engulfment by microglia

The fungus Cryptococcus neoformans causes lethal meningitis in humans with weakened immune systems and is estimated to account for 10-15% of AIDS-associated deaths worldwide. There are major gaps in our understanding of how this environmental fungus evades the immune system and invades the mammalian brain before the onset of overt symptoms. To investigate the dynamics of C. neoformans tissue invasion, we mapped early fungal localisation and host cell interactions at early times in infected brain, lung, and upper airways using mouse models of systemic and airway infection. To enable this, we developed an in situ imaging pipeline capable of measuring large volumes of tissue while preserving anatomical and cellular information by combining thick tissue sections, tissue clarification, and confocal imaging. Made possible by these techniques, we confirm high fungal burden in mouse upper airway turbinates after nasal inoculation. Surprisingly, most yeasts in turbinates were titan cells, indicating this microenvironment enables titan cell formation with faster kinetics than reported in mouse lungs. Importantly, we observed one instance of fungal cells enmeshed in lamina propria of upper airways, suggesting penetration of airway mucosa as a possible route of tissue invasion and dissemination to the bloodstream. We extend previous literature positing bloodstream dissemination of C. neoformans, via imaging C. neoformans within blood vessels of mouse lungs and finding viable fungi in the bloodstream of mice a few days after intranasal infection, suggesting that bloodstream access can occur via lung alveoli. In a model of systemic cryptococcosis, we show that as early as 24 h post infection, majority of C. neoformans cells traversed the blood-brain barrier, and are engulfed or in close proximity to microglia. Our work establishes that C. neoformans can breach multiple tissue barriers within the first days of infection. This work presents a new method for investigating cryptococcal invasion mechanisms and demonstrates microglia as the primary cells responding to C. neoformans invasion.

A Possible Link between the Environment and Cryptococcus gattii Nasal Colonisation in Koalas (Phascolarctos cinereus) in the Liverpool Plains, New South Wales

Cryptococcosis caused by yeasts of the Cryptococcus gattii species complex is an increasingly important mycological disease in humans and other mammals. In Australia, cases of C. gattii-related cryptococcosis are more prevalent in the koala (Phascolarctos cinereus) compared to humans and other animals, likely due to the close association that both C. gattii and koalas have with Eucalyptus species. This provides a cogent opportunity to investigate the epidemiology of spontaneous C. gattii infections in a free-living mammalian host, thereby offering insights into similar infections in humans. This study aimed to establish a link between nasal colonisation by C. gattii in free-ranging koalas and the tree hollows of Eucalyptus species, the key environmental source of the pathogen. We (i) detected and genotyped C. gattii from nine out of 169 free-ranging koalas and representative tree hollows within their home range in the Liverpool Plains, New South Wales, and (ii) examined potential environmental predictors of nasal colonisation in koalas and the presence of C. gattii in tree hollows. Phylogenetic analyses based on multi-locus sequence typing (MLST) revealed that the koalas were most likely colonised by the most abundant C. gattii genotypes found in the Eucalyptus species, or closely related genotypes. Importantly, the likelihood of the presence of C. gattii in tree hollows was correlated with increasing hollow size.

Comparing immunochromatography with latex antigen agglutination testing for the diagnosis of cryptococcosis in cats, dogs and koalas

Although the point-of-care cryptococcal antigen lateral flow assay (LFA) has revolutionized the diagnosis of cryptococcosis in human patients, to date there has been no large-scale examination of this test in animals. We therefore assessed the LFA in cats, dogs and koalas suspected of having cryptococcosis. In sum, 528 serum specimens (129 from cats, 108 from dogs, 291 from koalas) were tested using the LFA and one of two commercially available latex cryptococcal antigen agglutination test (LCAT) kits. The LCAT is a proven and well-accepted method in veterinary patients and therefore taken as the "gold standard" against which the LFA was compared. The LFA achieved a sensitivity of 92%, 100%, and 98% in cats, dogs, and koalas, respectively, with corresponding negative predictive values of 94%, 100%, and 98%. The specificity of the LFA was 81%, 84%, and 62% for cats, dogs, and koalas, respectively, with corresponding positive predictive values of 76%, 48%, and 69%. These findings suggest the most appropriate role for the LFA is as a screening test to rule out a diagnosis of cryptococcosis in cats, dogs, and koalas. Point-of-care accessibility makes it equally suited for use in the field and as a cage-side test in veterinary hospitals. The suboptimal specificity of the LFA makes it less suited to definitive confirmation of cryptococcosis in animals; therefore, all LFA-positive test results should be confirmed by LCAT testing. The discrepancy between these observations and the high specificity of the LFA in humans may reflect differences in the host-pathogen interactions amongst the species.

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

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.

Jet-Setting Koalas Spread Cryptococcus gattii VGII in Australia

Cryptococcus gattii molecular type VGII is one of the etiologic agents of cryptococcosis, a systemic mycosis affecting a wide range of host species. Koalas (Phascolarctos cinereus) exhibit a comparatively high prevalence of cryptococcosis (clinical and subclinical) and nasal colonization, particularly in captivity. In Australia, disease associated with C. gattii VGII is typically confined to Western Australia and the Northern Territory (with sporadic cases reported in eastern Australia), occupying an enigmatic ecologic niche. A cluster of cryptococcosis in captive koalas in eastern Australia (five confirmed cases, a further two suspected), caused predominantly by C. gattii VGII, was investigated by surveying for subclinical disease, culturing koala nasal swabs and environmental samples, and genotyping cryptococcal isolates. URA5 restriction fragment length polymorphism analysis, multilocus sequence typing (MLST), and whole-genome sequencing (WGS) provided supportive evidence that the transfer of koalas from Western Australia and subsequently between several facilities in Queensland spread VGII into uncontaminated environments and environments in which C. gattii VGI was endemic. MLST identified VGII isolates as predominantly sequence type 7, while WGS further confirmed a limited genomic diversity and revealed a basal relationship with isolates from Western Australia. We hypothesize that this represents a founder effect following the introduction of a koala from Western Australia. Our findings suggest a possible competitive advantage for C. gattii VGII over VGI in the context of this captive koala environment. The ability of koalas to seed C. gattii VGII into new environments has implications for the management of captive populations and movements of koalas between zoos.IMPORTANCE Cryptococcus gattii molecular type VGII is one of the causes of cryptococcosis, a severe fungal disease that is acquired from the environment and affects many host species (including humans and koalas). In Australia, disease caused by C. gattii VGII is largely confined to western and central northern parts of the country, with sporadic cases reported in eastern Australia. We investigated an unusual case cluster of cryptococcosis, caused predominantly by C. gattii VGII, in a group of captive koalas in eastern Australia. This research identified that the movements of koalas between wildlife parks, including an initial transfer of a koala from Western Australia, introduced and subsequently spread C. gattii VGII in this captive environment. The spread of this pathogen by koalas could also impact other species, and these findings are significant in the implications they have for the management of koala transfers and captive environments.

Cryptococcosis in the koala (Phascolarctos cinereus): pathogenesis and treatment in the context of two atypical cases

Disseminated cryptococcosis caused by Cryptococcus gattii (molecular type VGI) was diagnosed in an adult free-ranging female koala (Phascolarctos cinereus). Subclinical cryptococcosis was later diagnosed in this koala's joey. In the adult koala, a pathological fracture of the tibia was associated with the bone lysis of marked focal cryptococcal osteomyelitis. Limb-sparing orthopedic intervention, in the setting of disseminated cryptococcosis, was judged to have a poor prognosis, and the adult koala was euthanized. The joey was removed and hand-reared. Serological testing revealed persistent and increasing cryptococcal capsular antigenemia in the absence of clinical signs of disease and it was subsequently treated with oral fluconazole for approximately 16 months, rehabilitated and released into the wild. It was sighted 3 months post-release in a good state of health and again at 18 months post-release but was not recaptured on either occasion. This is the first published report of cryptococcal appendicular osteomyelitis in a koala. It is also the first report of concurrent disease in a dependent juvenile and the successful treatment of subclinical cryptococcosis to full resolution of the cryptococcal antigenemia in a free-ranging koala. This paper provides a discussion of cryptococcal osteomyelitis in animals, host-pathogen-environment interactions and treatment and monitoring protocols for cryptococcosis in koalas. Published reports describing the treatment of cryptococcosis in koalas are also collated and summarised.

ATYPICAL PRESENTATION OF CRYPTOCOCCUS NEOFORMANS IN A KOALA (PHASCOLARCTOS CINEREUS): A MAGNETIC RESONANCE IMAGING AND COMPUTED TOMOGRAPHY STUDY

Cryptococcosis is a worldwide and potentially fatal mycosis documented in wild and captive koalas ( Phascolarctos cinereus ) caused by Cryptococcus neoformans . Though mainly a subclinical disease, when the nasal cavity is affected, epistaxis, mucopurulent nasal discharge, dyspnea, and facial distortion may occur. This report describes a case of cryptococcosis in a koala where unilateral exophthalmos was the only evident clinical sign and magnetic resonance imaging and computed tomography findings are described. Both advanced imaging techniques should be considered as standard and complementary techniques for nasal cavity evaluation in koalas.

Equine Pulmonary Cryptococcosis: A Comparative Literature Review and Evaluation of Fluconazole Monotherapy

Cryptococcus is the most common fungal respiratory pathogen in Australian horses, manifesting primarily as pulmonary granulomas. Disease severity at presentation is dependent on the athletic use of the horse. The diagnosis and estimation of disease severity are centred around clinical findings, cytological evaluation of respiratory tract secretions, diagnostic imaging, and antigen titre testing. Both the lateral flow assay and the latex cryptococcal antigen titre are used, and important similarities and differences between species are discussed. Cryptococcus gattii occurs with greater frequency than Cryptococcus neoformans in equine pulmonic cryptococcosis and can be successfully treated with enteral fluconazole monotherapy, with disease severity determining treatment length.

Cryptococcus gattii infections

Understanding of the taxonomy and phylogeny of Cryptococcus gattii has been advanced by modern molecular techniques. C. gattii probably diverged from Cryptococcus neoformans between 16 million and 160 million years ago, depending on the dating methods applied, and maintains diversity by recombining in nature. South America is the likely source of the virulent C. gattii VGII molecular types that have emerged in North America. C. gattii shares major virulence determinants with C. neoformans, although genomic and transcriptomic studies revealed that despite similar genomes, the VGIIa and VGIIb subtypes employ very different transcriptional circuits and manifest differences in virulence phenotypes. Preliminary evidence suggests that C. gattii VGII causes severe lung disease and death without dissemination, whereas C. neoformans disseminates readily to the central nervous system (CNS) and causes death from meningoencephalitis. Overall, currently available data indicate that the C. gattii VGI, VGII, and VGIII molecular types more commonly affect nonimmunocompromised hosts, in contrast to VGIV. New, rapid, cheap diagnostic tests and imaging modalities are assisting early diagnosis and enabling better outcomes of cerebral cryptococcosis. Complications of CNS infection include increased intracranial pressure, severe neurological sequelae, and development of immune reconstitution syndrome, although the mortality rate is low. C. gattii VGII isolates may exhibit higher fluconazole MICs than other genotypes. Optimal therapeutic regimens are yet to be determined; in most cases, initial therapy with amphotericin B and 5-flucytosine is recommended.

Cryptococcus lacticolor sp. nov. and Rhodotorula oligophaga sp. nov., novel yeasts isolated from the nasal smear microbiota of Queensland koalas kept in Japanese zoological parks

A total of 515 yeast strains were isolated from the nasal smears of Queensland koalas and their breeding environments in Japanese zoological parks between 2005 and 2012. The most frequent species in the basidiomycetous yeast biota isolated from koala nasal passages was Cryptococcus neoformans, followed by Rhodotorula minuta. R. minuta was the most frequent species in the breeding environments, while C. neoformans was rare. Seven strains representing two novel yeast species were identified. Analyses of the 26S rDNA (LSU) D1/D2 domain and nuclear ribosomal DNA internal transcribed spacer region sequences indicated that these strains represent new species with close phylogenetic relationships to Cryptococcus and Rhodotorula. A sexual state was not found for either of these two novel yeasts. Key phenotypic characters confirmed that these strains could be placed in Cryptococcus and Rhodotorula. The names Cryptococcus lacticolor sp. nov. (type strain TIMM 10013(T) = JCM 15449(T) = CBS 10915(T) = DSM 21093(T), DDBJ/EMBL/Genbank Accession No.; AB375774 (ITS) and AB375775 (26S rDNA D1/D2 region), MycoBank ID; MB 802688, Fungal Barcoding Database ID; 3174), and Rhodotorula oligophaga sp. nov. (type strain TIMM 10017(T) = JCM 18398(T) = CBS 12623(T) = DSM 25814(T), DDBJ/EMBL/Genbank Accession No.; AB702967 (ITS) and AB702967 (26S rDNA D1/D2 region), MycoBank ID; MB 802689, Fungal Barcoding Database ID; 3175) are proposed for these new species.

Preshipment testing success: resolution of a nasal sinus granuloma in a captive koala (Phascolarctos cinereus) caused by Cryptococcus gattii

A 3-yr-old female koala (Phascolarctos cinereus) was diagnosed with a nasal sinus granuloma caused by Cryptococcus gattii after a pre-shipment examination revealed a latex cryptococcal agglutination titer of 1:512. Successful medical and surgical treatment of the granuloma was monitored using serial latex cryptococcal agglutination titers, serum levels of antifungal drugs, and advanced imaging.

Nasal mass removal in the koala (Phascolarctos cinereus)

Nasal masses in the koala (Phascolarctos cinereus) are not uncommon and can be challenging to diagnose and treat. Differential diagnoses for nasal masses in the koala are cryptococcal granulomas, nasal polyps, nasal adenocarcinoma, and osteochondromatosis. This report describes successful surgical approaches for two adult koalas with nasal masses and includes photodocumentation and description of the anatomy of the koala nasal passages from the postmortem transverse sectioning of a normal koala head. Surgical removal of the nasal masses in these koalas resulted in a rapid resolution of clinical signs.

Diversity of MHC class II DAB1 in the koala (Phascolarctos cinereus)

The host immune response is an important factor determining the outcome of the host–pathogen–environment interaction. At the gateway between the innate and adaptive immune systems are MHC molecules, which facilitate antigen presentation to T lymphocytes, and initiate the adaptive immune response. Despite their integral role in adaptive immunity, the genes encoding class II MHC molecules have not been examined directly in koalas. Furthermore, indirect historical evidence suggests that this species might lack functional diversity in class II MHC genes, with potential implications for disease susceptibility. We have examined diversity in the β chain genes of the koala class II MHC DA gene family and identified 23 alleles, including several atypical alleles. The levels of diversity observed are consistent with other marsupial and eutherian species, and do not support the paucity of variation suggested by the early literature. These findings are relevant to the conservation management of koalas and provide both a benchmark for maintaining population diversity and a platform for further conservation genetic research in this species.

Experimental models of cryptococcosis

Cryptococcosis is a life-threatening fungal disease that infects around one million people each year. Establishment and progression of disease involves a complex interplay between the fungus and a diverse range of host cell types. Over recent years, numerous cellular, tissue, and animal models have been exploited to probe this host-pathogen interaction. Here we review the range of experimental models that are available for cryptococcosis research and compare the relative advantages and limitations of the different systems.

Cryptococcus gattii: where do we go from here?

Infections caused by the emerging pathogen Cryptococcus gattii are increasing in frequency in North America. During the past decade, interest in the pathogen has continued to grow, not only in North America but also in other areas of the world where infections have recently been documented. This review synthesizes existing data and raises issues that remain to be addressed.

Long-term surveillance and treatment of subclinical cryptococcosis and nasal colonization by Cryptococcus neoformans and C. gattii species complex in captive koalas (Phascolarctes cinereus)

Cryptococcosis is an important systemic mycosis caused by members of the Cryptococcus neoformans species complex. This disease is potentially fatal in various animals, including koalas. We describe the long-term surveillance and treatment of subclinical cryptococcosis and nasal colonization of koalas by Cryptococcus neoformans and C. gattii. Of the 15 animals investigated through the use of samples obtained by nasal swabs, antigen titer measurements, and pathologic examination, C. neoformans was found associated with nine koalas and C. gattii with one animal. Nine koalas showed subclinical disease and one clinical infections and antigenemia. Treatment with fluconazole, itraconazole and amphotericin B upon detection of C. neoformans or C. gattii was not effective. The results of the present study showed that C. neoformans was the predominant species isolated from the nasal swab samples and the fungus might have naturally become associated with the koalas' nasal cavities at Kanazawa Zoological Gardens. The unclear treatment effectiveness might have been caused by a shorter treatment period that is routinely used and unstable itraconazole absorption. This investigation also underscores the need for identifying effective treatment regimens for subclinical cryptococcosis and efficient measures for eradicating C. neoformans and C. gattii in koalas.

Sequential opportunistic infections in two German Shepherd dogs

Two German Shepherd dogs with sequential opportunistic infections are described. The first was a 2-year-old male with cryptococcal rhinitis that spread to involve the optic nerves and brain. It was successfully treated with combination therapy utilising amphotericin B administered for 2 years, but the dog developed a disseminated Aspergillus deflectus infection 5 years later and was euthanased. The second case was a 4-year-old male that presented for a severe, deep-seated infection of the right antebrachium, with gradual extension to contiguous tissues. Neosartorya fischeri (anamorph; Aspergillus fischerianus) was isolated in pure culture and detected in histological sections. The infection was refractory to itraconazole, but resolved after amputation of the affected limb. Five months later, the dog developed a localised cutaneous lesion on the proximal pelvic limb, from which Pythium insidiosum was isolated and then visualised in tissue sections, together with a structure thought to be grass seed. This lesion was treated by wide surgical resection, although it was reported that the dog died of disseminated disease some months later. These cases provide further circumstantial evidence that young adult German Shepherd dogs have a predilection to developing invasive infections with fungi and other saprophytic pathogens.

Immunoproteomic approach to elucidating the pathogenesis of cryptococcosis caused by Cryptococcus gattii

Cryptococcosis caused by Cryptococcus gattii is a devastating disease of immunocompetent hosts with an incompletely understood pathogenesis. Utilizing an immunoproteomic approach in a naturally occurring koala model of disease, a number of key proteins and pathways are identified in the early and late pathogenesis of cryptococcosis for the first time. In particular, the thioredoxin system appears important in the pathogenesis of cryptococcosis caused by C. gattii VGII.

Pathogenesis of pulmonary Cryptococcus gattii infection: a rat model

A model of pulmonary cryptococcosis in immunocompetent rats was developed to better understand the virulence of Cryptococcus gattii. Six isolates were studied, representing four molecular genotypes (VGI-MATα, VGIIa-MATα, VGIIa-MAT a, VGIIb-MATα), obtained from Australia, Vancouver (Canada) and Colombia. These originated from human patients, a cat and the environment and were administered intratracheally (i.t.) or transthoracically into Fischer 344 or Wistar-Furth rats in doses varying from 10(4) to 10(7) colony-forming units (CFU) in 0.1 ml of saline. With the exception of animals given the VGIIa-MAT a isolate, rats consistently became ill or died of progressive cryptococcal pneumonia following i.t. doses exceeding 10(7) CFU. Affected lungs increased in weight up to tenfold and contained numerous circumscribed, gelatinous lesions. These became larger and more extensive, progressing from limited hilar and/or tracheal lesions, to virtually confluent gelatinous masses. Disease was localized to the lungs for at least 3-4 weeks, with dissemination to the brain occurring in some animals after day 29. The dose-response relationship was steep for two VGI isolates studied (human WM179, environmental WM276); doses up to 10(6) CFU i.t. did not produce lesions, while 10(7) or more yeast cells produced progressive pneumonia. Intratracheal inoculation of rats with C. gattii provides an excellent model of human pulmonary cryptococcosis in healthy hosts, mimicking natural infections. Disease produced by C. gattii in rats is distinct from that caused by C. neoformans in that infections are progressive and ultimately fatal.

Cryptococcosis in domestic animals in Western Australia: a retrospective study from 1995-2006

A retrospective study of cryptococcosis in domestic animals residing in Western Australia was conducted over an 11-year-period (from 1995 to 2006) by searching the data base of Murdoch University Veterinary Teaching hospital and the largest private clinical pathology laboratory in Perth. Cryptococcosis was identified in 155 animals: 72 cats, 57 dogs, 20 horses, three alpacas, two ferrets and a sheep. There was no seasonal trend apparent from the dates of diagnosis. Taking into account the commonness of accessions to Murdoch University, cats were five to six times more likely to develop this disease than dogs, and three times more likely than horses, while horses were almost twice as likely as dogs to become infected. Amongst the feline cohort, Ragdoll and Birman breeds were over-represented, while in dogs several pedigree breeds were similarly overrepresented. Dogs and horses tended to develop disease at an early age (one to five years), while cats were presented over a much wider range of ages. In cats and dogs the upper respiratory tract was the most common primary site of infection, while horses and alpacas tended to have lower respiratory involvement. The most striking finding of the study was the high frequency with which C. gattii was identified, with infections attributable to this species comprising 5/9 cats, 11/22 dogs, 9/9 horses and 1/1 alpaca, where appropriate testing was conducted. Preliminary molecular genotyping suggested that most of the C. gattii infections in domestic animals (9/9 cases) were of the VGII genotype. This contrasts the situation on the eastern seaboard of Australia, where disease attributable to C. gattii is less common and mainly due to the VGI genotype. C. gattii therefore appears to be an important cause of cryptococcosis in Western Australia.

Successful treatment of cryptococcal pneumonia in a pony mare

A 20-year-old Welsh Mountain Pony (212 kg) mare was initially presented for a chronic cough, fever, weight loss and low grade abdominal pain. She later developed dyspnoea, tachypnoea and exercise intolerance. The presence of multiple masses (up to 17 cm diameter) in the pulmonary parenchyma was established using lateral thoracic radiography and transthoracic ultrasonography. Encapsulated, budding yeasts were observed in smears made from transtracheal washings and needle aspirates of the pulmonary lesions. Cryptococcus gattii (synonym: Cryptococcus neoformans variety gattii; Cryptococcus bacillisporus) was cultured from the transtracheal washings and aspirates of the lung masses. The pony was successfully treated using daily intravenous infusions of amphotericin B (typically 0.5 mg/kg in 1 L 5% dextrose in water over 1 h, following premedication with 50 mg flunixin intravenously) over a 1 month period, until a cumulative dose of 3 g had been administered. Treatment was considered to be successful on the basis of progressive improvement in clinical signs, reduction in the size of pulmonary cryptococcomas, 48 kg weight gain and a reduction in the cryptococcal antigen titre from 4096 to 256, 1 year after cessation of treatment.

Evidence of recombination in mixed-mating-type and alpha-only populations of Cryptococcus gattii sourced from single eucalyptus tree hollows

Disease caused by the pathogenic yeast Cryptococcus gattii begins with the inhalation of an infectious propagule. As C. gattii is heavily encapsulated, this propagule is most likely to be a basidiospore. However, most C. gattii strains are infertile in laboratory crosses, and population studies indicate that recombination and dispersal are very restricted. In addition, strains of the alpha mating type predominate, which would not be expected in a mating population. C. gattii comprises four genetically distinct molecular genotypes, designated VGI to VGIV. C. gattii molecular type VGI has a strong association with Eucalyptus camaldulensis and can be found in high numbers in E. camaldulensis hollows. Previous work on isolates obtained from E. camaldulensis suggested that environmental populations of C. gattii are highly fragmented, have limited ability to disperse, and are confined to individual tree hollows. In the current study, we examined large numbers of isolates from three separate hollows for evidence of recombination. In two hollows, the alpha and a mating types were present in approximately equal numbers. The third hollow had alpha cells only and was from a region where a isolates have never been found. Statistical analysis of multilocus genotypes revealed recombining subpopulations in the three Eucalyptus hollows. Recombination was equally present in the alpha-a and alpha-only populations. This is consistent with recent studies that have found evidence suggestive of alpha-alpha mating in C. gattii and Cryptococcus neoformans and raises the possibility this may be a widespread phenomenon, allowing these fungi to recombine despite a paucity of a mating partners.

Microreview: capsule-associated genes of Cryptococcus neoformans

Cryptococcosis, caused by Cryptococcus neoformans is a common systemic mycosis in man and animals, particularly immunocompromised patients. This pathogenic fungus produces a thick extracellular polysaccharide capsule. Four capsule-associated genes (CAP10, CAP59, CAP60, CAP64) were cloned and sequenced, and proved to be essential for capsule synthesis. However biochemical functions of CAP gene products have not been clarified yet. Recently, the relatedness of the polysaccharide capsule and four capsule-associated genes has partly been elucidated. Nucleotide sequence of four CAP gene fragments was analyzed for phylogenetic relationships, and they were in agreement with the conventional classification of varieties and serotypes within C. neoformans. Expression of four CAP genes and capsule size were examined using two media containing different amount of glucose, and the results indicated that CAP genes might play important roles in elaboration of extracellular polysaccharide capsule. Furthermore, analyses of CAP genes in various clinical samples would give the useful information to diagnose cryptococcosis in human and animals.

Follow-up study of dogs and cats with asymptomatic Cryptococcus gattii infection or nasal colonization

The pathogenesis of Cryptococcus spp. infection following nasal colonization is unclear. This article reports follow-up data on a cohort of seven cats and five dogs identified in a previous study as sub-clinically infected with Cryptococcus spp. or colonized by C. gattii. Two cats progressed to clinical disease within four to six months of initial detection of antigenemia and nasal cavity colonization. The ten other animals remained asymptomatic but many were repeatedly positive on cryptococcal antigen testing or nasal fungal culture suggesting protracted infection or colonization. The results indicate that asymptomatically infected animals may clear the organism, remain sub-clinically infected or progress to clinical disease. Factors influencing the transition from exposure to disease require further investigation.

Sub-clinical infection and asymptomatic carriage of Cryptococcus gattii in dogs and cats during an outbreak of cryptococcosis

Since 1999, Cryptococcus gattii has emerged as an important pathogen of humans and animals in British Columbia, Canada. Nasal swabs and serum samples were collected from dogs and cats residing within the Coastal Douglas Fir biogeoclimatic zone on Vancouver Island, where clinical cases have been reported. Deep and superficial nasal fungal cultures of 280 dogs and 94 cats identified four (4.3%) cats and three (1.1%) dogs with C. gattii serotype B in their nasal cavity. Serum samples collected from 266 dogs and 84 cats identified six (7.1%) cats and two (0.8%) dogs with a positive cryptococcal antigen titer. Overall cats were 4.4 times more likely than dogs to be positive on one or both tests. Identification of sub-clinical infection and nasal colonization is an important step in the characterization of the outbreak of clinical cryptococcosis on Vancouver Island.

Retrospective study of feline and canine cryptococcosis in Australia from 1981 to 2001: 195 cases

A retrospective study of 155 cats and 40 dogs diagnosed with cryptococcosis between 1981 and 2001 was undertaken. Age, sex, breed, clinical findings, feline immunodeficiency virus and feline leukaemia virus status (in cats), species of Cryptococcus causing disease and region of domicile were recorded. Associations between variables were tested. Male and female cats were affected equally. Age ranged from 1 to 16 years, with a preponderance of cats aged between 2 and 3 years. Siamese, Himalayan and Ragdoll breeds were over-represented. Rural cats were more frequently infected with Cryptococcus gattii. Retroviral infection was not identified as a predisposing condition and was not correlated with either species of Cryptococcus or physical findings. Most cats had signs of nasal cavity infection, which was typically localised for a substantial period before invasion of adjacent structures or dissemination. Male and female dogs were affected equally. A marked preponderance of young, large breed dogs was noted. Border Collies, Boxers, Dalmatians, Dobermann Pinschers, Great Danes and German Shepherds were over-represented. Cryptococcus species involved was not affected by place of domicile. Although nasal cavity involvement was important, the canine cohort had a greater propensity to develop secondary central nervous system involvement and disseminated disease than feline cases. There were no clinical findings in either cats or dogs which could be reliably used to distinguish disease caused by Cryptococcus neoformans variety grubii from disease caused by Cryptococcus gattii. Both Cryptococcus species appear to be primary pathogens of cats and dogs, with the upper respiratory tract presumed to be the predominant primary site of inoculation in most but not all cases.

Clinicopathologic features of an unusual outbreak of cryptococcosis in dogs, cats, ferrets, and a bird: 38 cases (January to July 2003)

OBJECTIVE

To determine clinical and pathologic findings associated with an outbreak of cryptococcosis in an unusual geographic location (British Columbia, Canada).

DESIGN

Retrospective study.

ANIMALS

1 pink-fronted cockatoo, 2 ferrets, 20 cats, and 15 dogs.

PROCEDURE

A presumptive diagnosis of cryptococcosis was made on the basis of serologic, histopathologic, or cytologic findings, and a definitive diagnosis was made on the basis of culture or immunohistochemical staining.

RESULTS

No breed or sex predilections were detected in affected dogs or cats. Eleven cats had neurologic signs, 7 had skin lesions, and 5 had respiratory tract signs. None of 17 cats tested serologically for FeLV yielded positive results; 1 of 17 cats yielded positive results for FIV (western blot). Nine of 15 dogs had neurologic signs, 2 had periorbital swellings, and only 3 had respiratory tract signs initially. Microbiologic culture in 15 cases yielded 2 isolates of Cryptococcus neoformans var grubii (serotype A) and 13 isolates of C. neoformans var gattii (serotype B); all organisms were susceptible to amphotericin B and ketoconazole. Serologic testing had sensitivity of 92% and specificity of 98%.

CONCLUSIONS AND CLINICAL RELEVANCE

Serologic titers were beneficial in identifying infection in animals with nonspecific signs, but routine serum biochemical or hematologic parameters were of little value in diagnosis. Most animals had nonspecific CNS signs and represented a diagnostic challenge. Animals that travel to or live in this region and have nonspecific malaise or unusual neurologic signs should be evaluated for cryptococcosis.

Avian cryptococcosis

Clinical and laboratory findings in 15 unreported cases of avian cryptococcosis from Australia were collated and contrasted with 11 cases recorded in the literature. Cryptococcus species produced localized invasive disease of the upper respiratory tract of captive parrots living in Australia. This resulted in signs referable to mycotic rhinitis or to involvement of structures contiguous with the nasal cavity, such as the beak, sinuses, choana, retrobulbar space and palate. Parrots of widely differing ages were affected and of the seven birds for which sex was determinable, six were male. Cryptococcus bacillisporus (formerly C. neoformans var. gattii) accounted for four of five infections in which the species or variety was determinable, suggesting that exposure to eucalyptus material may be a predisposing factor. In these cases, Cryptococcus appeared to behave as a primary pathogen of immunocompetent hosts. One tissue specimen was available from an Australian racing pigeon with minimally invasive subcutaneous disease; immunohistology demonstrated a C. neoformans var. grubii (formerly C. neoformans var. neoformans serotype A) infection, presumably subsequent to traumatic inoculation of yeast cells into the subcutis. Two similar cases had been reported previously in pigeons domiciled in America. Data for parrots, one pigeon and other birds studied principally in America and Europe (and likely infected with C. neoformans) suggested a different pattern of disease, more suggestive of opportunistic infection of immunodeficient hosts. In this cohort of patients, the organism was not restricted to cool superficial sites such as the upper respiratory tract or subcutis. Instead, infections typically penetrated the lower respiratory tract or disseminated widely to a variety of internal organs. Finally, three captive North Island brown kiwis, one residing in Australia, the other two in New Zealand, died as a result of severe diffuse cryptococcal pneumonia (two cases) or widely disseminated disease (one case). C. bacillisporus strains were isolated from all three cases, as reported previously for another kiwi with disseminated disease in New Zealand.

Cryptococcus neoformans in the koala (Phascolarctos cinereus): colonization by C n. var. gattii and investigation of environmental sources

This study is the one in a series looking at the relationship among Cryptococcus neoformans var. gattii, koalas and the environment. The koala was used as a natural biological sampler in an attempt to understand the dynamics of C. neoformans var. gattii in Australian environments. Evidence of asymptomatic nasal and skin colonization for extended periods by large numbers of C. n. var. gattii was obtained and geographical factors assessed. The key finding was the ability of koalas to amplify numbers of C. n. var. gattii in certain environments. Koalas were not found to be obligatory for the survival of the organism in all environments. Geographical factors alone could not explain differing rates of nasal and skin colonization in koalas in different environments. A strong association between healthy koalas and C. n. var. gattii was confirmed and C n. var. gattii was isolated from novel sources, including the turpentine gum tree (Syncarpia glomulifera), tallowwood (Eucalyptus microcorys) and flooded gum (E. grandis). It seems likely that as yet undiscovered environmental sources of C. n. var. gattii exist in eastern Australia. Further investigation of host, environmental and organism factors integral to the hostpathogen relationship will assist an understanding of the progression from colonization to tissue invasion and cryptococcosis in all species.