Antarctica: Avian cholera identified as primary driver of mass Adélie penguin deaths, not H5N1 (2026)

Key findings

• A March 2024 international research expedition to Antarctica's Danger Islands, home to more than 1 200 000 breeding pairs of Adélie penguins, found thousands of dead penguins and carcasses of several other seabird species on two islands.
• Laboratory and pathological testing identified Pasteurella multocida (avian cholera) in 46 of 49 sampled animals, whereas H5N1 highly pathogenic avian influenza was detected in only a few, overturning the initial field suspicion that bird flu was the primary cause.
• Genetic analysis linked the outbreak strain to a P. multocida strain identified in Antarctic seabirds more than 20 years earlier and to strains detected more than 8000 km away in the Southern Ocean.
• The findings were published on 14 Oct 2026 in Proceedings of the Royal Society B, led by Matteo Iervolino (Erasmus University) with senior author Ralph Vanstreels (UC Davis One Health Institute).
• The expedition, known as the HPAI Australis Expedition, was funded by the International Association of Antarctica Tour Operators, Ocean Expeditions, and the European Union.