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Spread of Disease Linked to Warming Climate

By Douglas Fischer, Daily Climate editor

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A deadly infectious disease once thought to be exclusively tropical has gained a toehold in the Pacific Northwest, and health experts suspect climate change is partially to blame.

Last week the CDC issued a report warning U.S. doctors to be alert for patients showing signs of a cryptoccocal infection.

The infection is spread by a fungus, Cryptococcus gattii, that attacks the nasal cavity and spreads to other body sites, causing pneumonia, meningitis and other lung, brain or muscle ailments. The disease also affects animals.

Until 1999 most human cases were limited to Australia and other tropical and sub-tropical regions, including Asia and Africa, along with parts of southern California. 

But in 2004 the first case was reported in Oregon, and as of July 60 cases in the Pacific Northwest have been reported to the Centers of Disease Control and Prevention. Of the 45 cases in the region with known outcomes, nine patients died because of the infection and another six died with it, the CDC reported.

"This is not insignificant. These people died," said Dr. Ted Schettler, science director for the Massachusetts-based Science and Environmental Health Network, a group that advocates for the use of science in policy decisions.

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"When I went to medical school many years ago, Cryptococcus was a rare pathogen," he added. "If you saw it in a patient, it was someone who was immuno-compromised. Here now you're seeing it in the Pacific Northwest - where you wouldn't expect to see it - in people who wouldn't normally be sick."

The CDC alert stressed that other factors could be at play in the disease's spread besides climate change: The fungus may have adapted to a new climate niche, or environmental conditions favorable to C.gattii might be broader than suspected. 

Oregon epidemiologist Emilio DeBess, also the state veterinarian, cautioned against drawing direct links to climate change. "The answer is we really don't know," he said. "We need to step back a little bit and find out how diverse is this organism. That's going to tell us about the age - did it just show up or has it been here a long time."

But the CDC report notes that epidemiologists have ruled out increased disease awareness and reporting. And its emergence fits with the redistribution of infectious diseases predicted by various climate models, Schettler said.

"It's very consistent with the literature," he said. "It appears this was a pathogen finding a new home. It is just sort of interesting to put this alongside other parameters of climate change."

There are other recent examples of tropical pathogens exploiting newly hospitable ecosystems. 

  • Last week the CDC issued a bulletin on a dengue fever outbreak in Puerto Rico, noting that while the disease is common on the island, the most recent epidemic is large and started earlier than usual. 
  • Last year health researchers concluded warmer temperatures, higher humidity and increased precipitation - the types of weather forecast as greenhouse gas concentrations increase - have triggered higher rates of West Nile virus infection across the Western United States. (TDC - Changing climate ups West Nile threat in US - 20 Mar 2009)
  • And researchers at the University of Arizona suspect hotter temperatures and more intense dust storms are propelling an epidemic of Valley Fever across the Southwest. (TDC - Valley fever blowin' on a hotter wind - 15 April 2009)

DeBess was careful to put the Northwest's C.gattii outbreak in perspective. Only 60 cases have been detected over nearly six years in two or three states. Meanwhile 36,000 people die annually in the United States from influenza.

"It doesn't mean we aren't paying any attention," he said. "But you have to make your own decision: Do we worry about C.gattii, or do we worry about influenza more?"

DailyClimate.org is a nonprofit news service covering climate change. Reach editor Douglas Fischer at dfischer [ at ] dailyclimate.org

Photo credits: Transmission electron micrograph of C.neoformans, a closely related species to C.gattii and map showing spread of C.gattii into Pacific Northwest courtesy CDC.

DailyClimate.org is a nonprofit news service that covers climate change. This work by The Daily Climate is licensed under a Creative Commons Attribution-No Derivative Works 3.0 United States License.

Also read Nicole Heller's blog, The Climate Connection to Dengue Fever.

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