While heading towards the Danger Islands, Dr. Ralph Vanstreels suspected he’d encounter many dead Adélie penguins. It was March 2024, and a viral outbreak had been decimating wildlife in the region.
He was right about the dead penguins but wrong about the cause. Upon arriving at one of the islands, Vanstreels and his team immediately noticed mounds in the snow.
“Are those rocks or carcasses?” he wondered. “We had to dig through the snow to find out,” said Vanstreels, who works as a wildlife vet in Argentina with the University of California, Davis.
Ultimately, they discovered over 537 penguin carcasses on a landing ramp roughly the size of an airport runway. More bodies were scattered across the Danger Islands, home to two large penguin colonies. The team estimated thousands of dead Adélie penguins and other bird species, but they couldn’t conduct a thorough count due to time constraints.
“You can’t linger for too long there — an iceberg could trap you,” he noted.
As the investigation into the penguin die-off unfolded, Vanstreels believed it could provide insights into tracking global disease outbreaks.
The only continent that had escaped the virus — until now
Fast forward to Australia several months earlier, where another epidemic was brewing.
In June, H5N1 — a highly pathogenic form of avian influenza known as bird flu — made its way onto mainland Australia. Until then, Australia had been the only continent untouched by the virus that had swept across the globe, leaving dead birds in its path.
The virus is estimated to have killed nearly 300 million poultry birds since late 2021, whether through infection or culling to prevent its spread. Additionally, millions of wild animals and marine mammals have likely succumbed to bird flu, even if exact numbers are elusive.
Researchers were astonished that Australia remained bird flu-free for six years. Oddly enough, the virus didn’t arrive via the anticipated migratory routes from Southeast Asia; instead, it likely hitched a ride from Antarctica through migrating birds.
“This virus isn’t relying on airplanes to travel,” said Michelle Wille, a senior research fellow from the University of Melbourne. “It moves through mass mortality events.”
“The virus loads are low”
When Vanstreels set out to investigate the penguins, he presumed that bird flu was responsible. The virus had reached Antarctica in late 2023 and early 2024, prompting him and his colleagues to organize an expedition to clarify the situation.
The team initially prepared to search for bird flu, focusing on fears of a continuing global panzootic — a pandemic among animals. Dressed in multiple layers and protective gear, they began sampling the penguin remains.
“We looked a little awkward, like penguins ourselves, with all that gear,” he said, noting their adherence to strict biosafety protocols.
Samples were taken back to a lab aboard their vessel, and by evening, preliminary results started coming in. However, they weren’t what they had anticipated.
“There is bird flu present, but the virus loads are low,” he recalled, explaining that this was puzzling.
Since the carcasses were relatively fresh, Vanstreels expected a higher presence of the virus. This led him to think some other factor might have been at play. “We were quite uncertain about what was going on,” he remarked.
What the microscope revealed
So, what caused the death of the 500-plus penguins found on the ramp and the numerous others on the island?
Months later, back in the Netherlands, Vanstreels’ colleagues conducted follow-up research. “Under the microscope, we could see bacteria in the affected tissues,” he explained, indicating that a virus was not responsible.
The team identified a bacterial disease responsible for avian cholera, which, unlike human cholera, affects birds.
Vanstreels and his team’s findings were published in October in a scientific journal.
How concerning is avian cholera? Vanstreels stated that the disease doesn’t pose a significant threat to humans since the strains affecting birds and mammals are distinct. “Human infection risk isn’t really that high during bird outbreaks,” he added. However, the bacteria are lethal to birds globally, particularly in cold climates where they thrive.
There isn’t enough research to determine the prevalence of avian cholera, but the disease has been known among scientists for decades. Interestingly, the last dedicated study in the Antarctic Peninsula was 25 years prior.
“One might think that the incident from 2001 was just a rare occurrence, but it’s possible these die-offs happen regularly without scientists checking,” Vanstreels said, emphasizing the need for continued monitoring of bird diseases.
Antarctica isn’t as isolated as it seems
The mystery surrounding the cholera-infected penguins has scientists speculating about its origins. It’s hypothesized that the disease could have been introduced to Antarctica decades ago by researchers who brought poultry from the U.S.
Additionally, Dr. Gamble from Cornell University noted the strain of avian cholera found in Antarctica was very similar to one discovered far away on Île Amsterdam in the Southern Indian Ocean. “Antarctica is more connected to the rest of the world than we think,” she stated.
Tracking diseases in Antarctica is challenging, but Gamble pointed out its importance in the global pathogen puzzle. Monitoring responsibility has fallen to various countries as Antarctica isn’t governed by a single authority but is recognized as a continent of peace and science under an international treaty.
In conclusion, Gamble asserts that this avian cholera outbreak isn’t an isolated incident. “We really need to collaborate internationally,” she emphasized.
