Avian cholera caused penguin deaths in Antarctica

A large-scale die-off of Adélie penguins in Antarctica was triggered by avian cholera rather than bird flu, according to research appearing in the journal Biological Sciences. While biologists had feared high-pathogenicity avian influenza was responsible, diagnostic work proved that a bacterial infection caused the vast majority of the fatalities.

Scientists documented the die-off during an expedition that surveyed the remote Danger Islands in early 2024. That archipelago serves as a nesting territory for over 1.2 million Adélie penguin pairs. Across two different islands, observers found thousands of lifeless penguins alongside remains from several additional seabird varieties.

Because H5N1 had recently arrived at the Antarctic Peninsula, bird flu served as the initial working theory. Detailed tissue evaluations and laboratory screenings told an entirely different story, however. The microbe responsible for avian cholera, Pasteurella multocida, was identified in 46 out of 49 collected specimens. In contrast, the influenza virus turned up in merely a handful of cases.

Study co-author Ralph Vanstreels, a veterinarian working with the Latin America Program of UC Davis's One Health Institute, has spent years studying wildlife epidemics across Latin America and the polar south. He explained that although experts remain deeply troubled by avian influenza given its verified ties to regional bird casualties, this incident serves as a vital alert that different pathogens remain active in polar wildlife.

DNA profiling showed that the strain behind the deaths is closely connected to bacteria discovered in polar birds over twenty years ago. That connection suggests avian cholera has been present throughout the Antarctic zone for two decades or longer. The authors also found genetic similarities linking this variant to bacteria detected roughly 8,000 kilometers, or 5,000 miles, away in other parts of the Southern Ocean.

Lead investigator Matteo Iervolino, a researcher based at Erasmus University, noted that avian cholera might represent a broader and underappreciated driver of seabird deaths in Antarctica than scientists had previously realized. He stressed that ongoing health monitoring is crucial across isolated ecosystems so that dangerous disease events do not slip by without being noticed or analyzed.