Monday, April 25, 2016

EID Journal: Whole-Genome Analysis of Cryptococcus gattii, Southeastern United States

Credit CDC


While there are a number of mycotic diseases (Coccidioidomycosisis, Histoplasmosis, Blastomycosis, etc.) that are endemic to North America, a new fungus arrived in the Pacific Northwest from the tropics roughly 17 years ago, and has not only adapted to a much colder environment, it has picked up virulence as well. 

It is called Cryptococcus gattii, and it showed up unexpectedly on Vancouver Island in 1999, and has since then has spread into Washington and Oregon.

In 2010 the CDC’s Journal of Emerging Infectious Diseases published a research article on spread spread of C. gattii  in British Columbia (see A Fungus Among Us).  This fungus – a yeast really – is found in a number of species of trees (primarily Douglas fir & Western hemlock) and in the soil.  It can be spread by the wind, particularly during the warmer summer months.

This fungus has a wide host range, having been found to infect humans, cats, dogs, sheep, ferrets, llamas, elk, alpacas, and even porpoises (Cite).

Unlike its better known cousin C. neoformans which generally infects people with weakened immune system – C. gattii often infects those with healthy immune systems.  And unlike its behavior in the South Pacific (primarily Australia & New Guinea) – where it was usually seen causing neurological infections – this new cold-adapted strain tends to cause more pulmonary infections.

At least . . . that was the story . . . .

But as happens so often, the deeper scientists look, the more complex the story becomes.

Today's EID Journal carries a report that finds that C. gattii is not only more widespread in North America than previously believed - it may have been in the Southeastern United States far longer than in the Pacific Northwest.

Whole-Genome Analysis of Cryptococcus gattii, Southeastern United States

Shawn R. LockhartComments to Author , Chandler C. Roe, and David M. Engelthaler

Author affiliations: Centers for Disease Control and Prevention, Atlanta, GA, USA (S.R. Lockhart); The Translational Genomics Research Institute, Flagstaff, AZ, USA (C.C. Roe, D.M. Engelthaler)


Cryptococcus gattii is a recognized pathogenic fungus along the Pacific coast of the United States from California to Washington. Here we report that C. gattii may also be endemic to the southeastern United States and has probably been present there longer than in the Pacific Northwest.

The pathogenic fungus Cryptococcus gattii, recently designated as a separate species from Cryptococcus neoformans, is now recognized as a separate species complex (13). In the United States, C. gattii was not identified in culture collections until the late 1960s, when a substantial proportion of C. neoformans isolates from California were identified as serotypes B or C (now C. gattii serotypes A and B) (4,5). 
Since then, C. gattii has been identified not only in California but also in the Pacific Northwest (PNW) states of Washington and Oregon, where it is now considered endemic (68). Although non–travel-associated cases of infection, typically manifesting as pneumonia or meningitis, are occasionally reported in other areas of the United States (9,10), C. gattii has not been considered to be endemic to any other areas of the United States.



The first identified isolate of C. gattii in the United States was reported from West Virginia in 1924, although the isolate was not recognized as C. gattii VGI until decades later (14,15). Two other historical reports of C. gattii isolates from the southeastern United States exist: the first, from 1968, describes clinical and environmental isolates from Savannah, Georgia; the other, from 1982, describes isolates from Alabama, Tennessee, and Louisiana from patients with no travel history to a C. gattii–endemic region (16,17). 

Although both of these reports use the previous name for C. gattii, C. neoformans serotypes B and C, their results clearly indicate that C. gattii has existed in the southeastern United States for >40 years, as opposed to the recent emergence in the PNW during the past 2 decades. A more recent report describes a C. gattii VGI isolate from an HIV-positive patient in North Carolina (18); those authors surmised that the isolate was related to travel to San Francisco, but that assumption may have to be revised. 

No current molecular clock for C. gattii indicates the time required to generate the level of diversity seen in the VGI isolates. However, our findings lend credence to the hypothesis that C. gattii has circulated in the southeastern United States long enough to be considered endemic.

Dr. Lockhart is director of the Fungal Reference Laboratory, Mycotic Diseases Branch, Division of Foodborne, Waterborne, and Environmental Diseases, National Center for Emerging and Zoonotic Infectious Diseases, at CDC. His research interests include antifungal resistance and fungal population structure.

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