Avian cholera, not bird flu, killed 500-plus Adélie penguins in Antarctica
Researchers who sailed to the Danger Islands expecting to confirm bird flu instead found a bacterial disease, a result that raises questions about how pathogens move around the globe.
At a glance
- More than 537 Adélie penguin carcasses were found on one landing ramp in Antarctica's Danger Islands in March 2024.
- Tests showed low bird flu viral loads, and later microscope work identified bacteria that cause avian cholera.
- Researchers say the bacteria strain infecting birds differs from the mammal strain, so human risk is low.
A mass die-off of Adélie penguins in Antarctica's Danger Islands was caused by avian cholera, a bacterial disease, and not by the bird flu that researchers had expected to find, according to findings published in October in the journal Proceedings of the Royal Society B.
Dr. Ralph Vanstreels, a wildlife veterinarian based in Argentina with the University of California, Davis, reached the islands off the Antarctic Peninsula in March 2024, after a virus had swept through the area leaving dead birds behind. He and his colleagues counted more than 537 carcasses on a single landing ramp roughly the size of an airport runway. Thousands more penguins and other bird species died elsewhere on the islands, which host two penguin mega-colonies, but the team could not complete a count because an iceberg could block the only way out.
Searchers had to work through snow, checking whether each bump was a rock or a body. Wearing double gloves, coveralls, glasses and masks, they took samples from the carcasses and analysed them in a mini-lab aboard their boat. By evening, they had early results — and they were puzzling. Bird flu was present, but at low viral loads. The carcasses were fresh, so Vanstreels would have expected far more virus had influenza been the main killer.
Bacteria, not virus
Months later, colleagues in the Netherlands examined the samples under a microscope and found bacteria in the tissues. The team identified avian cholera, a bacterial disease distinct from human cholera.
Vanstreels says the disease is not considered a major threat to people, because the strain specialised to birds is distinct from the strain that infects mammals. It does kill birds worldwide, particularly in cold environments where the bacteria thrive.
How common avian cholera is remains unclear. The last time researchers looked for it on the Antarctic Peninsula was 25 years ago, which Vanstreels says can give a misleading impression that a 2001 event was a one-off. It is possible that die-offs happen regularly and simply go unchecked.
His main lesson from the episode: while bird flu demands attention, scientists should keep testing for other diseases that may be circulating alongside it.
Bird flu's long journey
Bird flu reached Antarctica in late 2023 and early 2024. In June, H5N1 arrived in mainland Australia, the last continent to be reached after six years without the virus. Researchers had expected it to arrive from Southeast Asia through migrating birds; instead it came from Antarctica. Since late 2021, nearly 300 million poultry birds have died or been culled to stop the spread, according to the World Animal Health Information System, and millions of wild animals and marine mammals are estimated to have died.
Dr. Amandine Gamble of Cornell University says the avian cholera strain found in Antarctic penguins is very close to one identified about 5,000 miles away on Île Amsterdam in the Southern Indian Ocean. Antarctica, she says, is far more connected to the rest of the world than people assume.
One theory is that avian cholera reached Antarctica decades ago with poultry brought by researchers from the United States. Tracking disease there is difficult, and with no single government in charge — the Antarctic Treaty, designated in the mid-20th century, now has 58 parties — the work depends on collaboration between many countries and their research stations.
Source: NPR News.
Questions and answers
- What killed the penguins in Antarctica's Danger Islands?
- Researchers identified avian cholera, a bacterial disease distinct from human cholera. The team expected bird flu, but found only low viral loads in the carcasses, and later found bacteria in the tissues.
- Is avian cholera dangerous to humans?
- Vanstreels says the risk of human infection from a bird outbreak is not high, because the strain specialised to birds is distinct from the strain that infects mammals.
- How did bird flu reach mainland Australia?
- Scientists had expected H5N1 to arrive from Southeast Asia through migrating birds. Instead, when it reached Australia in June, it came from Antarctica, the last continent the virus reached.
