13 Phylogenetic analyses, combined with recognized heterogeneity with respect to virulence, host preference, and antifungal susceptibility do provide evidence to support further taxonomic classification into a 7-species/4 hybrid species scheme ( Table 2). neoformans (serotype D or VNIV) and 5 other cryptic species, C gattii, C bacillisporus, C deuterogattii, C tetragattii, and C decagattii (serotypes B/C or VGI-IV). grubii (serotype A) with 3 genotypes (VNI, VNII, VNB) C neoformans var. At present, the following divisions have been proposed: C neoformans var. Recent proposed taxonomy changes based on the understanding of molecular studies have divided the pathogenic cryptococcal species from their classic divisions into better-defined molecular and genetic divisions. Molecular methods of identification have enhanced our appreciation for the significant genetic diversity among the C gattii– C neoformans complex and have called into question the current 2 species classification system. Historically, the genus was further classified into 3 varieties, 5 serotypes (based on structural differences in the polysaccharide capsule), and 8 molecular subtypes ( Table 1). 5– 8 These species differences in clinical presentation may be primarily determined by variable host predilections, but may also be better characterized as we further our understanding of molecular subtypes. However, preexisting conditions and immunocompromised states, including subclinical immune defects, are also reported as risk factors for infection with this species. C gattii, conversely, has historically been regarded as a pathogen of apparently immunocompetent patients. The epidemiology of C neoformans is well-characterized and this organism causes disease in both immunocompromised and apparently immunocompetent hosts. There are only 2 species commonly known to cause human disease, C neoformans and C gattii. THE PATHOGENS: CRYPTOCOCCUS NEOFORMANS AND CRYPTOCOCCUS GATTIIĬryptococcus is a genus of basidiomycetous fungi with more than 30 species ubiquitously distributed in the environment. 4 Despite increased availability of and success with antiretroviral therapy (ART), the worldwide burden of and mortality associated cryptococcal disease remains unacceptably high, and novel strategies of screening and preemptive therapy offer great promise at making a sustained and much needed impact on this sugarcoated opportunistic mycosis. As molecular techniques of identification have evolved, we have gained further insight into the pathobiology of these encapsulated yeasts, and their capacity to adapt to environmental pressures, exploit new geographic environments, and cause disease in both immunocompromised and apparently immunocompetent hosts. 3 Although C neoformans and C gattii share many features of a highly evolved, environmentally savvy yeast, there are important species- and strain-specific differences with respect to geographic distribution, environmental niches, host predilection, and clinical manifestations that should be emphasized. ![]() 1, 2 Over the last several decades, as vulnerable populations have expanded, cryptococcal meningitis became an infection of global importance, with up to 1 million new infections annually and significant attributable morbidity and mortality, especially among patients with human immunodeficiency virus (HIV) infection and AIDS. C neoformans was first identified as a human pathogen in the late 19th century, but was not recognized as a common cause of human disease until the late 1970s. ![]() Currently, there are 2 species of Cryptococcus that commonly cause disease in humans: Cryptococcus neoformans and Cryptococcus gattii. Cryptococcosis is an infectious disease with worldwide distribution and wide array of clinical presentations caused by pathogenic encapsulated yeasts in the genus Cryptococcus.
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