Life Threating Airborne Cryptococcus
Fungus Threatens U.S. and Canada
How did a life threatening tropical fungus end up in the U.S. and Canada? That's the puzzle researchers are attempting to solve after a new strain of hypervirulent, deadly Cryptococcus gattii fungus is creeping its way throughout North America.
The new strain is of the species the airborne fungus is native to tropical and subtropical regions, including Papua New Guinea, Australia, and parts of South America. An older strain of the fungus was first detected in North America in British Columbia, Canada, in 1999.
A strain recently emerged in Oregon where investigations have so far failed to find it in soil, water or trees. It may have arrived from abroad or originated locally, researchers said. The first U.S. Cryptococcus gattii cases were identified in 2005.
The organism has also attacks domestic and wild animals, according to the study, published April 22 in the journal PLoS Pathogens.
No one knows how the species got to North America or how the fungus can thrive in a temperate region, experts say.
"The alarming thing is that it's occurring in this region, it's affecting healthy people, and geographically it's been expanding," said study co-author Edmond Byrnes, a graduate student at the Joseph Heitman Lab at Duke University.
Cryptococcus gattii causes the human diseases of pulmonary cryptococcosis (lung infection), basal meningitis, and cerebral cryptococcomas. Occasionally, the fungus is associated with skin, soft tissue, lymph node, bone, and joint infections.
The environmental fungus emerged on Vancouver Island, British Columbia (BC), in 1999. By the end of 2006, it led to 176 cases and eight deaths - one of the highest burdens of C gattii disease worldwide.
Many cases presented with pulmonary findings, including cryptococcomas and infiltrates. One also presented with brain cryptococcomas. Cases were diagnosed by chest and brain imaging, and laboratory evidence including serum or cerebrospinal fluid cryptococcal antigen detection and culture of respiratory or cerebrospinal fluid specimens.
Less common than bacterial and viral infections, fungal diseases usually strike people with weakened immune systems—part of what makes the recent deaths of otherwise healthy people in Oregon so worrisome.
People can become infected with Cryptococcus gattii by inhaling the microscopic organisms—and there's not much you can do about it. . Pulmonary cases are typically treated with fluconazole which in itself can cause fatal liver disease.
There are no preventative measures available for the new strain, though the infection can be treated with antifungals, the study says. And "there are no particular precautions that can be taken to avoid Cryptococcosis," according to the British Columbia Centre for Disease Control.
The peculiar thing about Cryptococcus gattii is that it is causing serious infections in persons who were perfectly healthy. This poses two problems for the clinician. For one, most clinicians in North America are unfamiliar with it, as it has not caused outbreaks here before. That is, it has not been known to cause outbreaks here before. Two, most clinicians would not suspect a fungal infection as the cause of symptoms in an otherwise healthy person. It can be difficult to diagnose a condition, when the physician is thinking that the true cause is highly unlikely.
The good news is you cannot “catch” Cryptococcus from another person or animal, nor can an animal catch the disease from a human. Not all people who breathe the airborne yeast become ill. We know that almost a million people annually have been exposed to Cryptococcus, but only twenty –thirty per year become seriously ill. In pets, about thirty – forty animals are diagnosedwith the disease annually.
However, some of those who contract the illness can have very serious symptoms. In immunosuppressed patients, such as this patient, cryptococcal infections can causes meningitis, which may manifest on imaging as large, focal brain lesions. The treatment with systemic antifungal medical can be harsh.
There have been some unfounded reports of the possibility that an outbreak of a tropical disease in Canada and northwestern USA could be linked to climate change, however many experts are dismissing those claims as nothing more than rumours. Infectious disease specialist Alex Kazemi stated "there is absolutely no scientific evidence to conclude that Cryptococcus fungii are a consequence of climate change or global warming in any part of the world."
As with humans, nearly every fungus offspring represents a new combination of genes and their resulting traits. So it's possible that the new fast-spreading superfungi is the result of Cryptococcus gattii mating.
No matter how it arose, the tropical interloper looks like "it's going to stick around," Byrnes said, "at least for the foreseeable future."
Kelley Bergman is a media consultant, critic and geopolitical investigator. She has worked as a journalist and writer, specializing in geostrategic issues around the globe.
May 4, 2010