Duke Team Discovers a New Strain of Dangerous Airborne Fungus in Oregon and Expansion of Vancouver Island Fungal Outbreak to the United States

Durham, N.C. (February 2009) – A new strain of an airborne fungus has been discovered in Oregon, adding to a death toll that in recent years began in British Columbia. New cases of other subtypes associated with the ongoing Vancouver Island Outbreak arose in Washington and now in Oregon, in addition to a new, unique strain identified in Oregon, according to detailed molecular studies by researchers in the Duke University Department of Molecular Genetics and Microbiology and Center for Microbial Pathogenesis. The fungus can affect the lungs and breathing of patients and also can cause fatal meningitis.

Cryptococcus gattii, which used to be known as a tropical fungus, emerged to cause an outbreak on Vancouver Island starting in 1999, and has killed or sickened >300 people and animals, including 19 attributable deaths. The Duke research also shows that a new strain of the species is infecting people and animals in Oregon. This novel strain is from a new source, and so far has not been found in Canada.
 
Other subtypes of the fungus associated with the Vancouver Island outbreak are now also in the Northwestern US. “So far, the expansion of its range shows that it will likely further expand into California, and possibly also Nevada, Montana and Idaho,” said Edmond Byrnes, lead author of the study published in the online edition of the Journal of Infectious Diseases.

“A new fungal strain arises much less often than a new viral strain, which makes this organism important to study,” said Joseph Heitman, senior author of the study, published in an online edition of the Journal of Infectious Diseases. “We do not yet know how this new strain appeared in Oregon.” Between 2006 and 2008, 13 human cases in Washington and 9 in Oregon were all diagnosed with C. gattii infections.

Until very recently, the fungus was known to be in Australia and South America and was characterized as tropical. “Warming temperatures are not definitely a cause of its spread to a colder place, but that is a likely hypothesis,” Byrnes said.

These studies show definitively that the Vancouver Island VGIIa major genotype has spread into Washington and Oregon (14 out of 20 cases), one patient infected with the Vancouver Island VGIIb minor genotype was identified in Oregon, and five cases (three in humans, two in animals) in Oregon were attributable to the novel VGIIc genotype not found on Vancouver Island, Canada, or elsewhere.

The new Oregon strain defined by the Duke team, known as VGIIc, is noteworthy because it has never been found anywhere else in the world. The VGIIa subtype is the main cause of the Vancouver Island outbreak and is restricted to the Pacific Northwest.  The VGIIb subtype has been found both in Australia and on Vancouver Island in Canada. The molecular studies showed that the unique VGIIc strain has one allele (genetic sequence on a chromosome) that is not in any other VGII genotype.  How and where the VGIIc strain arose is not yet known.

In addition, dogs, cats, alpacas, and porpoises have been found to have the fungal infection. Other scenarios for distribution include waterborne spores in ocean and other water currents, or spores carried by human travelers. Because the infection is airborne, it cannot be easily avoided.

Given the travel history of the people and animals infected, most of the U.S. infections probably “were not the result of exposure on Vancouver Island or in Canada,” Heitman said. “This appears to be an emerging infectious disease in the Pacific Northwest within the United States.”

The fungus, which can infect both healthy and immunocompromised people, is a more aggressive fungus than its relative, Cryptococcus neoformans. Optimal treatment for C. gattii infections needs to be more aggressive, and the VGIIa genotype is particularly virulent in animal models of infection, which makes identification of both the species and molecular subtype important, Byrnes explained.

Collaborators for this study included Kieren Marr from Johns Hopkins University, Sheri Frank and Tom Mitchell from Duke University, and Robert Bildfell from Oregon State University.  These studies were supported by grants from the National Institutes of Allergy and Infectious Diseases of the NIH.

Contact: Mary Jane Gore