Cryptococcus gattii lives in the environment (1), usually in association with certain trees or soil around trees. Humans and animals can become infected with C. gattii after inhaling airborne, dehydrated yeast cells or spores (2), which travel through the respiratory tract and enter the lungs of the host (3). The small size of the yeast and/or spores allows them to become lodged deep in the lung tissue. The environment inside the host body signals C. gattii to transform into its yeast form, and the cells grow thick capsules to protect themselves (4). The yeasts then divide and multiply by budding. After infecting the lungs, C. gattii cells can travel through the bloodstream (5)—either on their own or within macrophage cells— to infect other areas of the body, typically the central nervous system (6).
Canadian scientists were baffled when in 2001, dead porpoises began washing up on the southeastern shore of Vancouver Island. Autopsies of the animals revealed their lungs were packed with flower-like tumors that left barely enough room for air.
Soon cats and dogs on the island started having trouble breathing, and people began coming to doctors with strange symptoms. They coughed constantly, had headaches and night sweats. X-rays showed lung and brain nodules, but the culprit wasn't cancer. When doctors biopsied the tissue, they discovered an alien strain of yeast.
Cryptococcus gattii as it was named, was once limited to the tropics and sub-tropics, but it suddenly jumped ship around 2000 and started appearing in a new and deadly form. Since then it's spread to mainland British Columbia, Washington and Oregon, and it shows no sign of stopping.
For more on this outbreak, we're joined by Jennifer Frazer, a freelance writer and blogger for Scientific American and the author of a piece about the fungus in this month's issue of the magazine.