Cryptococcus neoformans variety gattii

Case Report: Invasive Cryptococcosis in French Guiana: Immune and Genetic Investigation in Six Non-HIV Patients

Objectives

We describe the clinical, mycological, immunological, and genetic characteristics of six HIV-negative patients presenting with invasive cryptococcosis.

Methods

Patients with cryptococcosis without any of the classical risk factors, such as HIV infection, followed at Cayenne Hospital, were prospectively included. An immunologic and genetic assessment was performed.

Results

Five male patients and one female patient, 5 adults and one child, were investigated. All presented a neuromeningeal localization. Cryptococcus neoformans var. gattii and C. neoformans var. grubii were isolated in two and three patients, respectively, whereas one patient could not be investigated. Overall, we did not observe any global leukocyte defect. Two patients were found with high levels of circulating autoantibodies against Granulocyte macrophage-colony stimulating factor (GM-CSF), and none had detectable levels of autoantibodies against Interferon gamma (IFN-γ) Sequencing of STAT1 exons and flanking regions performed for four patients was wild type.

Conclusion

To better understand cryptococcosis in patients with cryptococcosis but otherwise healthy, further explorations are needed with repeated immune checkups and strain virulence studies.

Anti-granulocyte-macrophage colony-stimulating factor autoantibodies are a risk factor for central nervous system infection by Cryptococcus gattii in otherwise immunocompetent patients

Cryptococcosis is caused by either Cryptococcus neoformans or C. gattii. While cryptococcal meningoencephalitis is caused mostly by C. neoformans in immunocompromised patients, the risk factors remain unclear for patients with no known immune defect. Recently, anti-granulocyte-macrophage colony-stimulating factor (GM-CSF) autoantibodies were detected in the plasma of seven “immunocompetent” cryptococcosis patients, and the cryptococcal strains from these patients were reported as C. neoformans (three strains), C. gattii (one strain), and Cryptococcus (three strains not identified to the species level). We identified all three strains that had not been identified to the species level as C. gattii. Notably, the three strains that were reported as C. neoformans but were unavailable for species confirmation originated from Sothern California and Thailand where C. gattii is endemic. Most clinical laboratories designate C. neoformans without distinguishing between the two species; hence, these three strains could have been C. gattii. Since C. gattii infects more immunocompetent patients than C. neoformans, we pursued the possibility that this antibody may be more prevalent in patients infected with C. gattii than in those infected with C. neoformans. We screened the plasma of 20 healthy controls and 30 “immunocompetent” patients with cryptococcal meningoencephalitis from China and Australia (multiple ethnicities). Anti-GM-CSF autoantibodies were detected only in the plasma of seven patients infected by C. gattii and one healthy volunteer and in none infected by C. neoformans. While plasma from these C. gattii patients completely prevented GM-CSF-induced p-STAT5 in normal human peripheral blood mononuclear cells (PBMCs), plasma from one healthy volunteer positive for anti-GM-CSF autoantibodies caused only partial blockage. Our results suggest that anti-GM-CSF autoantibodies may predispose otherwise immunocompetent individuals to meningoencephalitis caused by C. gattii but not necessarily to that caused by C. neoformans.

Cryptococcal meningoencephalitis is the most serious central nervous system (CNS) infection caused by Cryptococcus neoformans or C. gattii. Cryptococcus primarily infects immunocopromised patients but is also sporadically encountered in otherwise “immunocompetent” patients with no known risk. In a recent study, anti-GM-CSF autoantibodies were detected in the plasma of seven otherwise immunocompetent patients with cryptococcal meningoencephalitis. Four of seven (57%) cryptococcal isolates from these patients were identified as C. gattii, while three strains were unavailable for species confirmation. We collected plasma from 30 otherwise healthy patients with CNS cryptococcosis in China and Australia (multiethnic) and analyzed the samples for the presence of anti-GM-CSF autoantibodies. The results suggest that anti-GM-CSF autoantibodies are a risk factor for CNS infection by C. gattii but not C. neoformans. GM-CSF may have a specific role in host defense against C. gattii, thereby elevating the importance of determining the level of anti-GM-CSF autoantibodies which can impact clinical management.

Projecting global occurrence of Cryptococcus gattii

This pathogen likely has wider distribution than is currently recognized.

Cryptococcus gattii and C. neoformans cause pulmonary and systemic cryptococcosis. Recently, C. gattii was recognized as a distinct pathogen of humans and animals. We analyzed information from 400 publications (1948–2008) to examine whether the fungus occurs globally. Known distribution of C. gattii is possibly limited because specialized reagents for differentiation from C. neoformans are not readily available and not always used, and environmental surveys are patchy. However, autochthonous reports of C. gattii cryptococcosis have now been recognized from tropical and temperate regions. An ongoing outbreak in western Canada strengthens the case that the range of the pathogen has expanded. A few studies have highlighted differences in cryptococcosis between C. gattii and C. neoformans. More than 50 tree species have yielded C. gattii especially from decayed hollows suggesting a possible ecologic niche. This pathogen merits more attention so its environmental occurrence and role in cryptococcosis can be accurately determined.

Cryptococcus gattii: An Emerging Cause of Fungal Disease in North America

During the latter half of the twentieth century, fungal pathogens such as Cryptococcus neoformans were increasingly recognized as a significant threat to the health of immune compromised populations throughout the world. Until recently, the closely related species C. gattii was considered to be a low-level endemic pathogen that was confined to tropical regions such as Australia. Since 1999, C. gattii has emerged in the Pacific Northwest region of North America and has been responsible for a large disease epidemic among generally healthy individuals. The changing epidemiology of C. gattii infection is likely to be a consequence of alterations in fungal ecology and biology and illustrates its potential to cause serious human disease. This review summarizes selected biological and clinical aspects of C. gattii that are particularly relevant to the recent North American outbreak and compares these to the Australian and South American experience.

Cryptococcus gattii: Emergence in Western North America: Exploitation of a Novel Ecological Niche

The relatively uncommon fungal pathogen Cryptococcus gattii recently emerged as a significant cause of cryptococcal disease in human and animals in the Pacific Northwest of North America. Although genetic studies indicated its possible presence in the Pacific Northwest for more than 30 years, C. gattii as an etiological agent was largely unknown in this region prior to 1999. The recent emergence may have been encouraged by changing conditions of climate or land use and/or host susceptibility, and predictive ecological niche modeling indicates a potentially wider spread. C. gattii can survive wide climatic variations and colonize the environment in tropical, subtropical, temperate, and dry climates. Long-term climate changes, such as the significantly elevated global temperature in the last 100 years, influence patterns of disease among plants and animals and create niche microclimates habitable by emerging pathogens. C. gattii may have exploited such a hitherto unrecognized but clement environment in the Pacific Northwest to provide a wider exposure and risk of infection to human and animal populations.

Spread of Cryptococcus gattii in British Columbia, Canada, and detection in the Pacific Northwest, USA

Cryptococcus gattii, emergent on Vancouver Island, British Columbia (BC), Canada, in 1999, was detected during 2003-2005 in 3 persons and 8 animals that did not travel to Vancouver Island during the incubation period; positive environmental samples were detected in areas outside Vancouver Island. All clinical and environmental isolates found in BC were genotypically consistent with Vancouver Island strains. In addition, local acquisition was detected in 3 cats in Washington and 2 persons in Oregon. The molecular profiles of Oregon isolates differed from those found in BC and Washington. Although some microclimates of the Pacific Northwest are similar to those on Vancouver Island, C. gattii concentrations in off-island environments were typically lower, and human cases without Vancouver Island contact have not continued to occur. This suggests that C. gattii may not be permanently colonized in off-island locations.

Unique hybrids between the fungal pathogens Cryptococcus neoformans and Cryptococcus gattii

Cryptococcus neoformans and Cryptococcus gattii are yeasts that cause meningoencephalitis, but that differ in host range and geographical distribution. Cryptococcus neoformans occurs world-wide and mostly infects immunocompromised patients, whereas C. gattii occurs mainly in (sub)tropical regions and infects healthy individuals. Anomalous C. neoformans strains were isolated from patients. These strains were found to be monokaryotic, and diploid or aneuploid. Amplified Fragment Length Polymorphism (AFLP) and sequence analyses indicated that AFLP genotypes 2 (C. neoformans) and 4 (C. gattii) were present. The strains were serologically BD. Mating- and serotype-specific PCR reactions showed that the strains were MATa-serotype D/MATalpha-serotype B. This study is the first to describe naturally occurring hybrids between C. neoformans and C. gattii.

Influence of climatic conditions on the isolation of members of theCryptococcus neoformansspecies complex from trees in Colombia from 1992–2004

The aim of this retrospective study was to analyze the relationship between occurrence of the serotypes of the Cryptococcus neoformans species complex in tree samples and the climatic conditions registered during samplings in four cities of Colombia, between 1992 and 2004, by means of a logistic regression model and lagged Pearson correlations. During 97 collection dates, 8220 samples from different tree species were taken, of which 2.63% were positive: 56.5% yielded serotype B, 24.7% serotype C and 18.8% serotype A isolates. The prevalence of the serotypes varied among the cities. The results suggest that environmental climatic conditions, mainly humidity, temperature, evaporation and solar radiation, can affect the occurrence of the different serotypes in trees in a differential manner. These different climatic tolerances were reflected in the geographic distribution of the serotypes in Colombia. The climatic conditions for 15 days before the sampling date were correlated with positive or negative isolation of the different serotypes.

Genetics of Cryptococcus neoformans

Cryptococcus neoformans is a pathogenic fungus that primarily afflicts immunocompromised patients, infecting the central nervous system to cause meningoencephalitis that is uniformly fatal if untreated. C. neoformans is a basidiomycetous fungus with a defined sexual cycle that has been linked to differentiation and virulence. Recent advances in classical and molecular genetic approaches have allowed molecular descriptions of the pathways that control cell type and virulence. An ongoing genome sequencing project promises to reveal much about the evolution of this human fungal pathogen into three distinct varieties or species. C. neoformans shares features with both model ascomycetous yeasts (Saccharomyces cerevisiae, Schizosaccharomyces pombe) and basidiomycetous pathogens and mushrooms (Ustilago maydis, Coprinus cinereus, Schizophyllum commune), yet ongoing studies reveal unique features associated with virulence and the arrangement of the mating type locus. These advances have catapulted C. neoformans to center stage as a model of both fungal pathogenesis and the interesting approaches to life that the kingdom of fungi has adopted.