Cryptococcus neoformans
Etiology/Bacteriology
Higher order taxa
Eukaryota (Kingdom); Fungi (Domain); Basidiomycota (Phylum); Tremellomycetes (Class); Tremellales (Order); Tremellaceae (Family); Cryptococcus (Genus)
Species
C. neoformans v. neoformans, C. neoformans v. grubii. A third variety, C. neoformans v. gattii, is now considered a distinct species, Cryptococcus gattii. Its teleomorph is Filobasidiella neoformans.
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NCBI: Taxonomy Genome: Cryptotoccus neoformans |
Description
Cryptococcus neoformans is an encapsulated fungal pathogen causing fatal meningitis primarily in immunocompromised humans. The infection is initiated by inhalation into the lungs, occurs mainly in immunocompromised individuals, but can also occur in healthy individuals. Cryptococcus neoformans is usually found in tissues in the yeast form. Infection of the brain and meninges is the most common clinical manifestation. In immunocompetent individuals, the initial infection is usually controlled and asymptomatic and the organism remains dormant in a lymph node complex, much like tuberculosis. Reactivation occurs in immunocompromised hosts where the fungus can spread via the blood to infect the central nervous system. Once C. neoformans reaches this stage it can cause meningitis that is uniformly fatal if untreated. Few antifungal agents exist and drug-resistant strains are emerging.
Genome structure
Most isolates of C. neoformans are haploid. The size of the genome is approximately 19 Mb with 14 chromosomes. Cryptococcus neoformans has a defined sexual cycle involving mating between cells of the MATalpha and MATa types. Thus, classical genetic approaches can be applied to study this organism.
Pathogenesis
Transmission
Virulence factors
Epidemiology
C. neoformans predominantly affects immunosuppressed hosts. Among HIV/AIDS patients, it is estimated that approximately 957,900 cases occur each year, resulting in nearly 625,000 deaths. Worldwide, 7-10% of patients with AIDS are affected. AIDS-associated cryptococcosis accounts for 50% of cryptococcal infections reported worldwide, usually occurring in HIV patients when their CD4 lymphocyte count falls below 200/mm3. In sub-Saharan Africa, the mortality rate is estimated to be between 50-70%. In developed countries such as the United States where therapy is available, the mortality rate is as low as 12%.
Clinical features
Diagnosis
Treatment
In healthy individuals, treatment is usually not necessary. However, it is recommended to receive check-ups for up to monitor any spreading of the infection. If there are lung lesions or the disease spreads, antibiotics such as fluconazole, itraconazole, and voriconazole may be prescribed.
