It sounds like something out of a bad science-fiction movie: polar explorers boldly forge ahead in a world of slowly melting ice, only to accidentally uncover and resurrect a deadly pathogen during the course of their research. Except in this case, it’s real life, and the victims are seals, not fictional scientists. It’s the result of global warming, which is changing the epidemiological landscape for both animals and people around the world.
This saga started in March 2012, when a large number of dead seals were discovered in Nova Scotia. They appeared to be healthy and in good physical condition, with no outward signs to explain their untimely deaths, or to provide insight into why nearly a fifth of an otherwise healthy grey seal colony was dead. Researchers performed necropsies on the bodies, and what they found was intriguing: a crescent-shaped parasite had ravaged through the livers of the animals, causing acute liver failure.
Where did it come from? The researchers learned that the grey seals were ranging further north in search of food, coming into contact with melting Arctic sea ice and into the range of ring seals, who also carry the parasite, known as Sarcocystis pinnipedi. Ring seals, however, don’t experience any ill effects from the infection, coexisting with the organism as they have been for centuries. In grey seals, who don’t have a history of parasitic exposure, it causes a devastating infection.
As grey seals range north and sea ice melts, carrying the parasite further south, it’s spreading through their populations. This isn’t the only example of an organism freed by global climate change, shifting away from its home environment to cause infections in animals and plants that aren’t equipped to handle it. The grey seals lacked adaptations to cope with the parasite because they hadn’t lived with it, just as many other animals are falling ill when they’re exposed to organisms from melting ice — and infectious agents from the equator, too.
Pathogens are moving more freely around the world not just because of the jet age, which allows a virus to board a plane in Singapore in the morning and be in New York within a matter of hours, but also because of ocean currents, shifting weather patterns, and more. As the climate becomes more disturbed, the rate of distribution may change as well, and parasites that have evolved to live with certain species of animals may cause dire infections in other members of the same genus. This could be a particular concern for fragile populations that might be easily disturbed by such infections.
What else is going to emerge from the ice? Researchers have already gone deliberately hunting for infectious organisms in the ice, like samples of the deadly 1918 flu, but it’s almost more frightening to think about what might be lying dormant that we don’t know about.
Many pathogens can remain stable in a dormant state for decades or centuries until conditions become more favorable — as, for example, when ice thaws and carries them into warmer waters and the bodies of potential hosts.
Photo credit: Marcel Burkhard.