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article imageHow a tropical pathogen came to reside in the Pacific Northwest

By Karen Graham     Jan 20, 2018 in Science
Flagstaff - In what is being described as “The Teddy Roosevelt effect,” a deadly fungus in the Pacific Northwest may have arrived from Brazil via the Panama Canal, according to a new study led by the Translational Genomics Research Institute (TGen).
Cryptococcus gattii is an encapsulated yeast found primarily in tropical and subtropical climates like Brazil, Australia or New Guinea. C. gattii is just one of several species of Cryptococcus. It is considered a pathogen and some strains of the fungus have proven to be especially virulent, with a mortality rate reaching 25 percent.
C. gattii can cause pulmonary cryptococcosis (lung infection), basal meningitis, and cerebral cryptococcomas. Occasionally, the fungus is associated with skin, soft tissue, lymph node, bone, and joint infections, and all-in-all is a rather nasty disease.
Cryptococcus infections were initially only seen in people with compromised immune systems, but C. gattii made its debut in North America with some fanfare when an outbreak of the deadly fungus occurred on Vancouver Island, British Columbia, Canada in 1999.
Old forest in Vancouver Island  British Columbia  typical environment where the spores of the tropic...
Old forest in Vancouver Island, British Columbia, typical environment where the spores of the tropical and sub-tropical fungus species Cryptococcus gattii may be found.
andiamotutti
From 1999 through 2003, the cases were largely restricted to Vancouver Island, then in between 2003 and 2006, the outbreak expanded into neighboring mainland British Columbia and then into Washington and Oregon from 2005 to 2009.
The case for C. gattii migration
There has been speculation the tropical fungus may have migrated to North America due to climate change, and global warming may have been a factor in its emergence in British Columbia, according to a study published in 2004.
This photomicrograph depicts Cryptococcus
This photomicrograph depicts Cryptococcus
Dr. Leanor Haley
The authors suggested the disease's presence on Vancouver Island came about through either the importation and/or changing climatic conditions that allowed distribution and thriving of C. gattii propagules into new ecological niches.
Now, a new study by researchers at the Flagstaff, Arizona-based Translational Genomics Research Institute (TGen) is suggesting the deadly fungus in the Pacific Northwest may have arrived from Brazil via the Panama Canal in what they are describing as “The Teddy Roosevelt effect."
The researchers used genomic analysis and advanced statistics to trace the probable evolution of the disease, correlating it in time to the 1914 opening of the Panama Canal and the resulting surge of shipping trade between Brazil and the Pacific Northwest. The results were published January 18, 2018, in the journal mSphere.
Cryptococcus gattii growing in a petri dish.
Cryptococcus gattii growing in a petri dish.
By Djspring (Own work) [CC-BY-SA-3.0 (http://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia
“Understanding the emergence and continual evolution of this pathogen into a new environment is critical to the understanding of the ongoing spread of cryptococcal disease, and may be important to studying the evolution of other emerging health threats,” said Dr. David Engelthaler, Director of TGen’s Pathogen and Microbiome Division and the study's senior author.
Genome sequencing was done on 134 C. gattii samples. Then estimating mutation rates along with using evolutionary analysis, the team was able to calculate the arrival of C. gattii in the Pacific Northwest in the last 60 to 100 years. The authors say this “makes a strong case for an anthropogenic (human-caused) introduction.”
The Teddy Roosevelt effect
When the Panama Canal, commissioned by Theodore Roosevelt, was completed in 1914, it more than likely provided the perfect migratory route for a number of "foreign invaders," or non-native flora and fauna into North America. And C. gattii is believed to have chosen this route, even though it may not have realized what was happening.
View of the Miraflores Locks in the Panama Canal near Panama City on June 22  2016
View of the Miraflores Locks in the Panama Canal near Panama City on June 22, 2016
Rodrigo Arangua, AFP/File
The Panama Canal opened trade between South and North America, and at first, trade was in hardwood lumber, minerals, coffee, and rubber. However, researchers in this study propose that contaminated ballast water — which has spread animals, algae, and microbes across the globe, is one way C. gattii may have arrived.
“Whatever the cause of C. gattii to the PNW, it is clear that those populations are neither ancient nor very recent (less than 25 years) arrivals to the region,” the authors state, and dispersal in the last 100 years “would strongly suggest a human cause, rather than animal migrations, as proposed with the slower evolution and spread of Valley Fever and other disease-causing fungi."
Basically, you could look at this study as another page in the history of humankind and our close connection to people and cultures around the world, including their pathogens and other diseases. And as the authors point out, when Teddy Roosevelt's canal was opened, it "allowed, for the first time in nearly 3 million years, water movement between the Atlantic and Pacific Oceans."
More about Panama canal, Cryptococcus gattii, teddy roosevelt effect, Deadly fungus, Vancouver island
 
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