Infectious Diseases

Cryptococcus Gattii Deadly Strain of Fungus Spreading in the us



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Researchers have recently published a study on a fungal infection commonly found in the tropics, that has spread into British Columbia and is now spreading south into the Pacific Northwest. Infection is rare, with only 21 infections to date in the U.S., but researchers are concerned that doctors unaware of its existence will not be able to diagnose it.

Cryptococcus gattii is a fungus that traditionally affects eucalyptus trees in tropical and subtropical climates. It is a close relative of Cryptococcus neoformans, which infects almost one million people a year and kills over 600,000. C. neoformans normally occurs in people with compromised immune systems, such as transplant recipients and HIV patients. C. gattii affects people with healthy immune systems, but at low incidences. It was first noted in Vancouver Island in 1999, and began spreading into Washington and Oregon in 2005. The cases in Oregon appear to be a recently-developed strain of the fungus. The new strain seems to be more dangerous than the original: it has killed 25% of its U.S. victims, as opposed to under 10% in Canada. C. gattii has never before appeared in a temperate climate, which suggests that the new strain is capable of living in a greater range of environments. 

C. gattii lives mainly in Douglas fir and western hemlock in Canada. Although several cases of infection have occurred in the United States, no wild instances of the fungus have yet been detected. It mainly affects construction and woodworkers, and those who spend a lot of time in contact with soil. The disease has been documented in several mammals, including humans, porpoises, dogs and cats, livestock, and elk. A sample preserved from an early-70’s Seattle patient tested positive for C. gattii, although that patient’s travel history is unknown. 

The disease cannot be transferred from person to person, or from animals to people: it is carried as spores that travel on the wind. Symptoms include coughing, night sweats, pneumonia, and weight loss. Meningitis occurs in some cases. There is no prevention, but the infection can be treated with six weeks of intravenous antifungals, followed by six months of oral fluconazole. Researchers are hoping to use DNA sequencing to detect whether a person is infected with the virulent or a more benign form of the fungus.

C. gattii is expected to expand at least to Northern California, which has a climate similar to that of Oregon. It is not expected to travel eastward, as freezing can kill the fungus, and it is unlikely to be able to overwinter in the colder regions.

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