C. gattii is closely related to the more widespread infectious yeast, Cryptococcus neoformans. The potentially life-threatening C. neoformans invades the central nervous system to cause disease. It most commonly affects immune-compromised patients such as organ transplant recipients and cancer patients -- whose immune systems are crippled by immunosuppressive drugs or chemotherapy -- and people with HIV/AIDS. In contrast, C. gattii infects individuals with apparently normal immunity. Symptoms include persistent headaches, coughing and night sweats. In rare cases, C. gattii causes cryptococcal disease, pneumonia, meningitis or death.
While C. neoformans is found worldwide in association with pigeon droppings, the rarer C. gattii is normally restricted to tropical and subtropical areas, often in association with Eucalyptus trees.
"It is suspected that the infectious propagules of Cryptococcus are airborne spores," Heitman said. "Such spores are produced during sexual reproduction, though mating of the fungus has never been observed in nature."
In plants and animals, sexual identity is governed by sex chromosomes, Heitman explained. In fungi, however, sexual identity is determined by so-called "mating type loci," genes arranged contiguously, but which typically do not span an entire chromosome. Cryptococcus exists in two mating types, "a" and "alpha," determined by a single genetic region, or locus.
Earlier studies by the Duke team found that most Vancouver Island outbreak isolates are sexually fertile, but all are of one "sex," a trend that would seem to preclude the normal sexual cycle. A recent laboratory study led by Heitman's group suggested a possible explanation: the related yeast C. neoformans can undergo same-sex mating between two alpha part
Source:Duke University Medical Center