Potentially lethal fungus moves south from Canada
A potentially lethal fungus normally found only in the tropics has established a foothold on the Pacific Coast of British Columbia and has slowly made its way southward into Washington, Oregon and Idaho, researchers said Thursday.
Health authorities are not unduly alarmed by the fungus because the number of cases so far remains small, but both federal and state officials — including those in California — are monitoring its progress in the fear that it will spread more rapidly as it reaches warmer climates.
“Overall, I don’t think it is a large threat at this time,” said molecular biologist Edmond J. Byrnes III of Duke University Medical Center, the lead author of the report appearing in the online journal PLoS Pathogens. “But the fact that it is continuing to spread geographically and the number of cases is rising makes it a concern.”
FOR THE RECORD:
Lethal fungus:: An article in Friday’s Section A about a potentially lethal fungus said four human cases had been reported in California. Three cases have been reported in the state.
The spread is also a concern because the strain of the fungus that moved into the U.S. in 2004 has mutated to become more lethal than the original strain that invaded British Columbia in 1999.
Five of the 21 people who contracted the fungus in the U.S. have died (about 25%), compared with 8.7% of the 218 infected people in Canada. The fungus has also infected many different species of mammals.
“This is really big news in the world of people who study [fungi],” said mycologist Karen Bartlett of the University of British Columbia, who was not involved in the current research but who is one of the leading experts on the outbreak. “It’s of clinical health importance because of the fact that the diagnosis can potentially be missed by physicians and veterinarians” because they don’t know about this new fungus.
The fungus in question is called Cryptococcus gattii, which is found primarily in tropical and subtropical regions. It is a close relative of Cryptococcus neoformans, which kills more than 600,000 people annually in such regions. C. gattii’s primary habitat in Canada is about 10 species of trees, primarily Douglas fir and western hemlock.
C. gattii seems to infect primarily healthy people, while its close relatives — for which it can easily be mistaken — primarily infect those with a compromised immune system. Physicians seeing its symptoms in an otherwise healthy person thus might not think to look for it.
It is not transmitted from person to person or carried by insect or animal vectors. C. gattii, like all fungi, forms spores that are blown in the wind or moved around by disturbances of the soil. They can easily be carried on the soles of shoes, for example.
The spores are inhaled and colonize the lungs, and then they spread throughout the body. The primary symptoms include prolonged coughing, night sweats, pneumonia and weight loss over a period of weeks. Meningitis can occur, which produces severe headaches. Treatment involves six to eight weeks of intravenous antifungal medications, such as amphotericin B, followed by up to six months of oral fluconazole.
“We need physicians to be aware of this and think about it when they see symptoms of infection,” said epidemiologist Julie Harris of the mycotic diseases branch of the Centers for Disease Control and Prevention. “This is a serious infection, but so far it’s a rare infection.”
The primary victims of infection have been people who spend a lot of time outdoors, often in contact with soil, and those who do woodwork and construction, Harris said.
So far, researchers have found almost no instances of the fungus in the environment in the U.S., Byrnes said. The 21 cases in humans and about three times that number in animals have been widely dispersed, in cities, suburbs and rural areas. The animals that have contracted it are species that don’t travel, and there are no common denominators to any of the infections, he said.
Four human cases, none of whom died, and four in animals have been observed in California, according to Dr. Ben Sun, the state public health veterinarian.
The fungus is not traveling eastward “because we don’t think it will ever be able to live in the Sierra Nevada,” Bartlett said. “Could it go down the Central Valley of California? Yeah, probably. But it will be intermittent, not a homogenous spread.”