Warmer January Temperatures May Favor Expansion of Cryptococcus gattii in Northwest North America

Computer modeling predicts where potentially lethal fungus may spread

Newswise — Researchers in British Columbia, Canada, have used a technique known as ecological niche modeling to identify likely areas where a potentially lethal fungus could spread next. Cryptococcus gattii, which can cause life-threatening infections of the lungs and central nervous system when inhaled, infects humans as well as a broad range of wild and domestic animals.

In a study published in the May 2010 issue of the peer-reviewed journal Environmental Health Perspectives, Canadian researchers found that the optimal ecological niche areas of the fungus in British Columbia are limited to the central and southeastern coasts of Vancouver Island, the Gulf Islands, the Sunshine Coast, and the Vancouver Lower Mainland. Although this represents less than 2 percent of the province’s land area, two-thirds of British Columbia’s population lives there, the authors noted. They hypothesized that the San Juan Islands and Puget Trough of Washington State and the Willamette Valley of Oregon may become endemic areas for the fungus, whose spores are dispersed by the wind, animals, and humans.

The study is important because C. gattii is expanding into new ecological areas, making its spread difficult to predict. Once thought to be limited to tropical and subtropical regions, including Australia, Africa, Italy, South America, and Southern California, the fungus now is found in the temperate rainforests of the Pacific Northwest. Reports elsewhere suggest the fungus may have been exported from its native habitat on commercially valuable trees such as eucalyptus and several ornamental species.

C. gattii appeared on Vancouver Island in 1999, and by the end of 2008 it had sickened more than 240 humans and 360 animals, giving British Columbia one of the highest incidences and largest multispecies outbreaks of cryptococcosis in the world, the study recounted. Approximately 25 new human cases of cryptococcosis are now identified each year in British Columbia.

Because field sampling for the presence of a pathogen across a province of nearly 945,000 square kilometers (about 365,000 square miles) is not feasible, the authors theorized that a more practical solution would be to use ecological niche modeling, which analyzes data collected through human and animal surveillance and environmental sampling. For the model they built, which outlined where the fungus is currently established and forecast where it might spread, the researchers reported a predictive accuracy exceeding 98 percent.

The optimal niche for C. gattii is characterized by elevations averaging 100 meters above sea level, daily January average temperatures higher than 0°C (32°F), and location within biogeoclimatic zones populated by specific types of trees, according to the authors, who include Sunny Mak, Brian Klinkenberg, Karen Bartlett, and Murray Fyfe.

“Ecological niche modeling, traditionally developed for biodiversity and conservation research, recently has been employed by public health to predict the geographic risk of infectious diseases,” Mak explains. “This is a new tool that we have to inform strategies for disease surveillance, environmental sampling, and public and physician awareness of Cryptococcus gattii infections.”

The full research article, “Ecological Niche Modeling of Cryptococcus gattii in British Columbia, Canada,” is available on the EHP website at http://ehponline.org/article/info:doi/10.1289/ehp.0901448.

EHP is published by the National Institute of Environmental Health Sciences (NIEHS), part of the U.S. Department of Health and Human Services. EHP is an open-access journal. More information is available online at http://www.ehponline.org. Brogan & Partners Convergence Marketing handles marketing and public relations for the publication and is responsible for creation and distribution of this press release.