Tracking disease outbreaks to the ends of the Earth

The ominous text arrived when National Geographic Explorer Jane Younger was aboard a research vessel in Antarctica’s Weddell Sea: “More dead crabbies.” It was from a friend working as an expedition leader on a nearby cruise ship. He had spotted dead crabeater seals on the edge of the sea ice. Younger was studying how the bird flu sweeping the globe was circulating in the region, and the sighting suggested that the virus had jumped to crabeaters.

But it was also a potential piece of a much larger puzzle. Antarctica is one of the fastest warming places on Earth—temperatures are rising on the continent at two times the global average—fueling an expected increase in emerging diseases over the next 50 years. The continent’s ecosystem is a “canary in the coal mine” for how climate change will reshape global disease outbreaks, says Younger, a molecular ecologist at the University of Tasmania.

Younger and a team of scientists on the Schmidt Ocean Institute’s R.V. Falkor (too) set a course for the dead seals’ last location. The group was part of the National Geographic and Rolex Perpetual Planet Ocean Expeditions, an expansive project sending researchers to study the Earth’s five oceans. After three and a half days navigating icy waters in December of last year, they arrived. But by then, everything had changed. An ice edge had broken into small pieces, which made searching the large area by ship hopeless. So they launched a drone.

Soon the drone’s camera zeroed in on a lone crabeater seal, dead and partially frozen into a drifting chunk of ice. Younger and Amandine Gamble, a veterinarian and researcher at Cornell University, navigated to the seal in a Zodiac. Flu viruses concentrate in the brain, so the pair carefully broke through the thick braincase with a screwdriver and hammer, inserted a long swab, swirled it through the exposed tissue, and sealed it in a vial of buffer solution.

Back in Australia, the specimen was tested at Younger’s lab. The seal had bird flu—the first verified case in an Antarctic ice seal. It marked an alarming milestone in the virus’s relentless spread. Since 2021, the H5N1 subtype has proliferated across continents, killing millions of birds and many thousands of marine mammals. In South America the disease has ravaged sea lion colonies, killing tens of thousands of the animals. In Antarctica the stakes are especially high.

As the planet warms and more animals move toward the poles, researchers expect diseases to spread to new territories, leaving Antarctic wildlife vulnerable. “Seals are long-lived, slow to breed, and top predators,” Younger says. “Losing them could have long-lasting effects on the ecosystem that we can’t yet predict.”

In addition to seals, the team sampled penguins and scavenging birds. Only the scavengers—kelp gulls, skuas, and sheathbills—had antibodies, meaning they’d been exposed to the virus but lived through the infection. Penguins didn’t have antibodies, suggesting they may not have been surviving exposure. “That’s what’s so worrying,” Younger says. “They’re not eating carcasses like the scavengers are, so they’re less likely to be exposed—but if they are, it looks like they’re dying.”

How is the virus getting to Antarctica? Samples from two animals were traced to South America. The likely vectors, Younger says, are migratory birds. Some giant petrels and skuas breed in Antarctica or on sub-Antarctic islands and travel vast distances as part of their migration—sometimes through South America and into Asia—before returning south. Their globe-spanning journeys may have brought the virus in more than once, seeding it in new locations each time.

Younger’s long-term goal is that fieldwork like hers will be the lifeblood of an early-warning system for disease in the Southern Ocean. Much as meteorologists use atmospheric data to forecast storms, she envisions harnessing genetic information and on-the-ground observations to track pathogens. This system would help scientists intervene before a virus kills large populations of wildlife.

Younger is optimistic that in the future scavenging birds could serve as sentinels, offering early warnings of outbreaks. Eventually, they might even become vaccination targets, she says, to help protect more vulnerable populations, like penguins, before viruses get to them. “Antarctica offers a unique starting point,” Younger says, “to test and refine the tools we need before scaling them worldwide.”