A US-led research team has reported that a newly discovered strain of an airborne fungus more commonly found in the tropics, has killed several people in Oregon and is set to spread among humans and animals, progressing from the Pacific Northwest towards California.
You can read about the emergence and virulence of new genotypes of Cryptococcus gattii fungi in the United States in a report of a study led by Duke University Medical Center in Durham, North Carolina, online in the 22 April issue of PLoS Pathogens.
Co-lead author Edmond Byrnes III, a graduate student in the Duke Department of Molecular Genetics and Microbiology, told the media:
“This novel fungus is worrisome because it appears to be a threat to otherwise healthy people.”
“Typically, we see this fungal disease associated with transplant recipients and HIV-infected patients, but that is not what we are seeing,” he added.
The newly discovered strain of C. gattii has so far killed 25 per cent of the 21 people in the Pacific Northwest whose cases have been analyzed: this compares with 8.7 per cent mortality out of 218 cases infected by a less virulent strain in British Columbia, Canada, said the researchers, adding that infection by C. gattii tends also to follow a more complicated course than infection by the more common Cryptococcus neoformans.
However, according to a report in ABC News, the authorities do not appear to be seriously alarmed about the outbreak because the number of cases is relatively small. However, both federal and state officials are following the situation very closely as there is concern that it will spread more quickly when it reaches warmer regions.
Infection by C. gattii can be treated, but there is no vaccine or other way to prevent it.
The more virulent strain appears to have genetically recombined with less virulent ones, creating a new genotype (VGIIc) that is highly infectious, and a major source of illness in Oregon, compared to strains that are not causing outbreaks.
The researchers have not been able to trace the precise origin of VGIIc: they have tested soil samples, water and trees from Oregon, with no success.
In humans, symptoms often appear between two and several months after exposure, when people usually develop a cough that lasts several weeks, feel sharp chest pains, become short of breath, experience headaches, fever and night sweats and also lose weight.
When animals become infected they usually get a runny nose, have problems breathing, experience nervous system problems and get raised bumps under their skin.
Byrnes said they found the new virulent or Oregon strain in many types of animal, including domesticated ones like cats, dogs, alpaca and sheep. Most of the animals involved are not migratory, he said, suggesting that the fungus has not spread by animals migrating from one region to another.
Co-lead author Dr Wenjun Li, of Duke Molecular Genetics and Microbiology, suggests that environmental changes may be responsible for the evolution and emergence of new strains of C. gattii, which is more commonly found in the tropics.
Some strains of C. gattii are not more virulent than C. neoformans, and doctors need to know the difference between the virulent strains and less virulent ones as it affects treatment plans, said the researchers.
The only way to tell the difference between the virulent and more benign strains is to grow a culture of the fungus and then analyze its DNA, explained the researchers, who used molecular techniques to show that the Oregon strain probably emerged recently, in additon to an outbreak that started in Canada in 1999 and then spread to Washington and Oregon.
Co-author Yonathan Lewit, a research associate with Duke Molecular Genetics and Microbiology, said they were trying to track the evolution of the strains by studying the genes of all the samples they get hold of.
He explained that the mitochondria (cell components that have their own separate DNA) could be responsible for the increased virulence of some of the strains.
Grants from the National Institutes of Health/National Institute of Allergy and Infectious Diseases helped pay for the research.
“Emergence and Pathogenicity of Highly Virulent Cryptococcus gattii Genotypes in the Northwest United States.”
Edmond J. Byrnes, III, Wenjun Li, Yonathan Lewit, Hansong Ma, Kerstin Voelz, Ping Ren, Dee A. Carter, Vishnu Chaturvedi, Robert J. Bildfell, Robin C. May, and Joseph Heitman.
PLoS Pathog; 2010 6(4): e1000850; Published online 22 April 2010.
DOI:10.1371/journal.ppat.1000850
Source: Duke Medicine, ABC News.
Written by: Catharine Paddock, PhD