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Tropical Fungus Might Have Reached Pacific Northwest Via Ballast Tanks, Tsunami

By Nicholas Gerbis
Published: Monday, October 14, 2019 - 5:05am

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Life cycle of C. gattii
Life cycle of C. gattii

A tropical fungus affecting the lungs and central nervous system unexpectedly appeared in the Pacific Northwest 20 years ago.

A new hypothesis suggests a novel mechanism for how it came ashore: a tsunami.

The findings appear in the American Society for Microbiology journal mBio.

Genomic analysis of Cryptococcus gattii shows it likely arrived in the region from South America between seven and nine decades ago, possibly carried in the ballast water of ships passing through the Panama Canal.

The authors of the new paper assert it then lingered in the coastal waters until a tsunami carried it ashore in 1964.

The tidal wave was spawned by the Great Alaskan Earthquake that occurred in Prince William Sound, Alaska, on March 27 of that year. At magnitude 9.2, it was the most powerful earthquake ever recorded in U.S. history.

Co-author David Engelthaller, director of TGen North, says tsunamis could prove a fascinating subject of study for theoretical epidemiologists.

"This really is kind of a new area to think about for infectious disease ecology and epidemiology — the impact of natural disasters on really changing the microbe ecology in an environment," he said.

Engelthaller was also senior author on the 2018 paper in the journal mSphere that proposed the ballast water hypothesis.

Prior work by researchers at the Centers for Disease Control and Prevention has established an association between tsunamis and fungal diseases. Survivors of near-drownings, too, have experienced fungal skin and pulmonary illnesses.

The authors hypothesize the fungus took three decades to adapt to its new environment before its detection in 1999.

C. gattii is able to grow a protective outer layer, which might have helped it survive and evolve in the waters off the coast of mainland British Columbia, Vancouver Island, Oregon and Washington.

Other hypotheses for its dispersal include contaminated shipments, ocean and wind currents, and ecological alterations brought about by climate change.

C. gattii is a microscopic fungus that lives in soil around certain trees. It infects humans and animals that breathe in its airborne cells or spores. Several months can pass before symptoms appear.

In the lungs, a C. gatti cryptococcosis infection can cause chest pain, coughing, fever and shortness of breath. From there, it can enter the bloodstream and infect the central nervous system, where it can cause a form of meningitis.