Avian Cholera Killed Antarctic Penguins

A mass die-off of Adélie penguins in the Danger Islands was caused by avian cholera, not the bird flu virus that scientists initially feared. The finding, published in October in the journal Proceedings of the Royal Society B, resolves a mystery that unfolded in March 2024 when a disease swept through the region near the Antarctic Peninsula.

Dr. Ralph Vanstreels, a wildlife veterinarian at the University of California, Davis, led a team to the area expecting to find evidence of H5N1. The researchers discovered more than 537 carcasses on a single landing ramp, an area Vanstreels compared to the size of an airport runway. While they estimated thousands of birds died across the two mega colonies on the islands, the team could not complete a full count due to ice conditions.

The team collected samples from the deceased birds and tested them in a laboratory on their boat. Initial results showed the presence of bird flu, but the virus loads were unexpectedly low for a recent death. Vanstreels noted that the carcasses were not old enough for the virus to be the primary cause if it had killed them directly.

Further analysis in the Netherlands revealed bacteria in the tissues, identifying the pathogen as avian cholera. This disease, distinct from human cholera, is not considered a major threat to people because the strain specialized in birds differs from the mammalian strain. However, the bacteria thrive in cold environments and kill birds worldwide.

Dr. Amandine Gamble, an assistant professor at Cornell University, stated that the strain found in Antarctica is very close to a strain found 5,000 miles away on Île Amsterdam. She added that Antarctica is more connected to the rest of the world than previously thought. A theory suggests avian cholera may have been introduced decades ago by researchers who brought poultry from the United States.

The discovery follows the arrival of H5N1 in mainland Australia in June, which ended a six-year period where the continent remained free of the virus. Since late 2021, the avian influenza virus has resulted in the death of nearly 300 million poultry birds globally, either through infection or culling. Michelle Wille, a senior research fellow at the University of Melbourne, described the virus's spread as occurring through mass mortality events rather than human transport.

The Antarctic Treaty, which has 58 parties including the U.S., France, Japan, and Russia, governs the continent through international cooperation. Gamble emphasized that the outbreak is not a unique event and that continued international collaboration is necessary to track pathogens that cross borders.