On March 27, 1964, Alaska’s Prince William Sound region was hit by a 9.2-magnitude earthquake, the strongest one ever recorded in North America. Around 139 people died, largely due to the series of tsunamis that swelled along the continent’s west coast in the wake of the seismic event. Now, a study published in mBio argues that the Great Alaska Earthquake also unleashed a deadly fungus along the Pacific Northwest Coast, with lasting implications for both humans and the natural environment.
Since 1999, the region has been dealing with an ongoing outbreak of Cryptococcus gattii, a microscopic, yeast-like fungus that can cause infections if it is inhaled. Most people who are exposed to C. gattii do not get sick, but those who do become ill are at risk of pneumonia, skin infections, meningitis and nodules in the lungs and brain. In rare instances, the fungus can be fatal.
More than 300 C. gattii cases have been reported in Canada and the United States, and the fungus does not only impact humans; it has been found in animals, too. The source of these infections seems to be the C. gattii that has been discovered lurking in the soil, trees and shore waters of the Pacific Northwest Coast. But curiously, nearly all of the fungal subtypes isolated from sick patients resemble subtypes typically seen in Brazil and other parts of South America. In fact, prior to the Pacific Northwest outbreak, experts had thought that C. gattii was restricted to the tropical and subtropical climates of South America, Africa, Asia, and Australia, raising the question of how the fungus had travelled to North America.
Over the years, scientists have proposed a number of theories about modes of dispersal, including ocean and wind currents, animal movements, and the shipment of agricultural products. In 2017, David M. Engelthaler, co-author of the new report, was among a number of researchers who suggested that increased traffic stemming from the opening of the Panama Canal in 1914 brought C. gatti to the north, possibly in the water of ships’ ballast tanks. Analysis of the three C. gattii populations found in the Pacific Northwest suggested that the timing was right, with their most recent common ancestor occurring within the last 60 to 100 years.
But questions still lingered. For one, how did C. gattii get from oceans and estuaries into trees and soil? For Engelthaler and his co-author, Arturo Casadevall, the Great Alaska Earthquake offered a compelling and explanation.
“This one event, like no other in recent history, caused a massive push of ocean water into the coastal forests of the [Pacific Northwest],” they write. “Such an event may have caused a simultaneous forest C. gattii exposure up and down the regional coasts, including those of Vancouver Island, BC, Canada, Washington, and Oregon.”
Engelthaler and Casadevall bolster their theory with several pieces of evidence. For one, genetic analyses of Pacific Northwest C. gattii strains point to a single introduction event. What’s more, the fungus exists primarily in coastal forests, rather than further inland, which suggests a “connection to the shoreline,” according to the study authors.
The researchers also had to explain why, if the fungus washed ashore in North America in 1964, it took 35 years for an outbreak to start. Casadevall had previously found that a close C. gattii relative can evolve to become even more potent after being preyed upon by amoebas in the wild—and the study authors think something similar may have been happening in the decades after the Great Alaska Earthquake.
"We propose that C. gattii may have lost much of its human-infecting capacity when it was living in seawater, but then when it got to land, amoebas and other soil organisms worked on it for three decades or so until new C. gattii variants arose that were more pathogenic to animals and people," Casadevall explains.
But the researchers note that the earliest case of one Pacific Northwest C. gattii strain actually occurred in Seattle in 1971, long before the outbreak began in 1999, which in turn suggests that the fungus was already present in the region.
This piece of evidence, like the others cited by the study authors, is circumstantial. But Engelthaler tells Gizmodo’s Ed Cara that he and Casadevall “haven’t found data that would discount or disagree with the hypothesis,” and that “there is no good alternate hypothesis that fits all the data.”
Moving forward, the researchers hope to advance their theory by studying whether C. gatti subtypes found in the Pacific Northwest and other parts of the world are more prevalent around ports. Looking at areas that have been hit by tsunamis is particularly important because, as Casadevall notes, the “big new idea here is that tsunamis may be a significant mechanism by which pathogens spread from oceans and estuarial rivers onto land and then eventually to wildlife and humans.”
And if the researchers are correct in their hypothesis that C. gatti can percolate for decades after reaching the shore, tsunami-affected areas like Indonesia and Japan could also be at risk of future outbreaks. “[I]f C. gattii was found in coastal waters of areas that have suffered tsunamis in recent decades,” the study authors write, “this could allow real-time studies in those areas and perhaps forestall future outbreaks of cryptococcosis in these locales.”