The researchers said their findings provide important additional insight into the origin of the Vancouver Island outbreak, which began in 1999. Moreover, the evidence that sex played an important role in the pathogen's expansion may provide a useful model for the evolution of infectious diseases and parasites more generally, they said.
The team reported its findings October 9, 2005, in an advanced online publication of Nature. The work was supported by the National Institute of Allergy and Infectious Disease.
After extensive genetic analysis of fungal samples, the researchers suggest that mating between two less harmful fungal strains of the same sex or "mating type" produced the more virulent form. That strain has now taken hold and appears to be spreading -- perhaps driven by unique conditions in the Vancouver area, they said.
"While the number of people infected so far does not approach that of many other infectious diseases, this fungus is invading the central nervous systems of people who have no other apparent risk factors except having taken a walk in the park on Vancouver Island," said Joseph Heitman, M.D., Ph.D. "A year after infection, some of these people still have not fully recovered.
"The fungus appears to have become entrenched in the Vancouver Island area," he added. "It is unlikely to disappear, and all indications are that it is spreading. Our findings suggest that sex played a role in the expanded geographic range for this pathogen."
Since it was first documented in 1999, C. gattii has infected at least 100 people on Vancouver Island
Contact: Kendall Morgan
Duke University Medical Center