Lethal fungus strain moving from Canada to US

Tuesday 27 April 2010 00:00

A newly discovered strain of virulent airborne fungi that has already killed several people in Oregon in the US Pacific Northwest could reach California and other areas, scientists warn.

But infections from the new genotypes of Cryptococcus gattii fungi (or C. gattii), first reported in 2005, are not common and are not transmitted between humans, thus reducing the risk of an epidemic, according to a study published Thursday in the journal PLoS Pathogens.

The mortality rate for recent C. gattii cases in the Pacific Northwest runs at about 25 percent of 21 cases analyzed in the United States.

The rate was only 8.7 percent in the western Canadian province of British Columbia, out of 218 cases, since an outbreak of an older strain that began in 1999 before gradually spreading south.

"This novel fungus is worrisome because it appears to be a threat to otherwise healthy people," said study co-author Edmond Byrnes, a graduate student at the Duke University Department of Molecular Genetics and Microbiology.

"Typically, we see this fungal disease associated with transplant recipients and HIV-infected patients, but that is not what we are seeing."

The strains found in Canada and the US Pacific Northwest are both part of the C. gatti species and can be distinguished by observing their DNA sequences, according to study senior author Joseph Heitman, chair of the Duke Department of Molecular Genetics and Microbiology.

The predominant strain emerged from Vancouver Island, British Columbia, before spreading to Oregon and Washington. But the new genotype that is now a major source of C. gattii illness in Oregon, called VGIIc, "is not present anywhere else," Heitman told AFP.

He stressed that infections and deaths from the fungi are "very rare."

About half of C. gattii patients do not have an underlying medical condition, while the other half has some health issues and different risk factors, Heitman added.

For their study, researchers tested the fungus by culturing it and then sequencing its DNA to determine whether it was the virulent or more benign strain.

The geneticists uncovered clues using molecular techniques that showed the Oregon-only genotype likely arose recently, in addition to Canada's C. gattii outbreak that began 11 years ago.

Symptoms, which can appear two to several months after exposure, can include a cough that lasts several weeks, sharp chest pain, shortness of breath, headache, fever, nighttime sweats and weight loss.

Infected animals will show symptoms including a runny nose, breathing difficulties, nervous system problems and raised bumps under the skin.


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