Since 1999, hundreds of people have fallen sick with a mysterious infection in Canada and the US Pacific Northwest region. Could a 1964 tsunami be to blame?
That’s the idea behind a new study published in the journal mBio. Researchers from the Translational Genomics Research Institute in Arizona and Johns Hopkins University argue that tsunamis resulting from the Great Alaskan Earthquake of 1964, the largest ever documented in the northern hemisphere, may have washed ashore a tropical fungus called Cryptococcus gattii that continues to wreak havoc to this day.
"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," Arturo Casadevall, study co-author and microbiologist at Johns Hopkins, explains in a statement.
"If this hypothesis is correct, then we may eventually see similar outbreaks of C. gattii, or similar fungi, in areas inundated by the 2004 Indonesian tsunami and 2011 Japanese tsunami."
C. gattii fungal Infections typically occur through inhalation of the spores and eventually result in a nasty pneumonia-like illness that may also spread to the brain. There have been at least 300 cases on the east coast of North America and approximately 10 percent of those people have died.
The first case of a C. gattii infection emerged on Vancouver Island in 1999. Before this, the infection had only been reported in Papua New Guinea, Australia, and South America.
Somehow, the tropical fungus managed to make the mammoth voyage across the Pacific Ocean and up the coast of America, while missing out California. But how? The new study puts forward a few theories: it hitchhiked on a migrating flock of black swans, it latched onto eucalyptus trees imported from the tropics, it was transported in the ballast tank of ship, or it was spat up from the sea following the Great Alaskan Earthquake.
At first glance, the tsunami theory might seem the least likely since there were 35 years between the natural disaster and the first reports of infection. However, a closer look reveals that this might be the most plausible explanation, the researchers say.
Evidence of C. gattii can be found in the soil and trees of coastal areas in British Columbia, Washington, and Oregon, as well as the bodies of marine animals. Scientists used "molecular clock" analysis to DNA sequence C. gattii and found that one subtype came from Brazil 60 to 100 years previously to arriving in the Pacific Northwest. This matches up to the time that the Panama Canal opened in 1914, connecting the Atlantic Ocean with the Pacific Ocean.
This evidence would point to cargo ships transporting the fungi, however, it also became clear that several different subtypes of the fungus had all washed ashore en masse at the same time. Whatever transported the fungus did so in a colossal singular event – like a tsunami – not multiple intermittent journeys.
As for the 35-year gap of inactivity, previous research has shown that other Cryptococcus species evolve different defenses if they dwell in seawater. While this is good for fending off wild amoeba, it weakens their capacity to infect humans.
"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," explained Casadeval.