July 17, 2014  Print

A highly virulent fungus, which has killed several people in the Pacific Northwest of America and was originally thought to have originated in Australia, has now been shown by Australian researchers to have most likely originated in Brazil.

Researchers say the potentially deadly variant of the fungus Cryptococcus gattii, which is highly adaptive and evolving as it spreads from the tropics to temperate climates, warrants global “public health vigilance.”

An international team led by Professor Wieland Meyer from the Westmead Millennium Institute for Medical Research found that C. gattii has several genes which make outbreak strains more capable of surviving colder environments and also make lung infections caused by the fungus more deadly.

The study’s senior investigator, Professor Meyer is the head of the Molecular Mycology Research Laboratory at the Centre for Infectious Diseases and Microbiology, Marie Bashir Institute at Westmead Millennium Institute, and Professor for Molecular Medical Mycology at the University of Sydney, Sydney Medical School at Westmead Hospital.

“By closely analyzing the genomes of more than one hundred globally isolated C. gattii strains, including the Pacific Northwest and Vancouver Island outbreak strains, we identified numerous genes potentially related to habitat adaptation, virulence expression and to clinical presentation,” said Professor Meyer.

“We also found evidence that the Pacific Northwest strains originated from South America, and not Australia as previously thought.”

C. gattii is an airborne fungus native to tropical and subtropical regions, including Australia, Papua New Guinea, and parts of South America.
It was originally thought to be an exclusively tropical fungus before it was discovered in 1999 in the temperate environments of Vancouver Island, in the Canadian state of British Columbia. 

The Canadian strain not only established a new environmental niche, but soon evolved into a new, more virulent, pulmonary disease than quickly spread to mainland Canada and south into the state of Washington.

That was followed by an outbreak in Oregon of a new strain causing deadly lung infections — dubbed “The Killer Fungus” by the US media — which also spread throughout the Pacific

In order to understand the emergence of C. gattii in new environments, a collaborative team of 24 researchers from 13 institutions in seven nations conducted one of the largest-ever global fungal genome analyses of a specific fungal species.

The WMI team, in collaboration with the Translational Genomics Research Institute in the United States, sequenced 115 genomes collected from 15 countries.

Professor Meyer said the study, published in the scientific journal mBio, the leading journal of the American Society for Microbiology, should form the basis of additional investigations about how and why C. gattii disperses and emerges.

“By analyzing the genomes of C. gattii globally collected we were able to compare and determine the genomic differences that may cause their clinical and ecological changes,” he said.

“The study identified several new genomic targets for diagnostic tests, and possible new targets for therapeutic drugs and preventative vaccines.

The study’s co-investigator Professor Tania Sorrell, who is the Director of WMI’s Centre for Infectious Diseases and Microbiology and Director of the Marie Bashir Institute at the University of Sydney, said the study suggested public health officials should be on the lookout for C. gattii, even in regions where it is not thought to be endemic.

“The genetic ability of the fungus to adapt to new environments, as shown by our research, suggests that a high level of vigilance would be prudent.”

Professor Sorrell said that new tests developed for the study were making it easier to detect C. gattii and other fungi, and could lead to better monitoring and treatments.

“Further elucidation and characterization of these genetic features may lead to improved diagnostics and therapies for infections caused by this continually evolving fungus.”