‘Cautious optimism’ now that penguins test positive for bird flu, but show no symptoms

Adélie penguins in Antarctica are testing positive for bird flu without showing outward signs of illness, according to researchers who traveled around thirteen remote breeding sites on an ice-breaking cruise ship.

Since bird flu arrived in the region this year, there have been concerns that the virus could reach Antarctica’s vulnerable penguin populations. In November last year, researchers warned in a pre-print research paper that if the virus were to cause mass death in these colonies, “it could signal one of the greatest ecological disasters of modern times.”

In December 2023 and January 2024, scientists tested 16 Adélie penguins on Beagle Island on the Antarctic Peninsula for H5N1, and seven (43%) tested positive. Satellite trackers of the penguins showed them alive and foraging normally two months later, in early March 2024. At another location on Red Rock Ridge, nine Adélie penguins were tested and one tested positive.

None showed any sign of illness, which is good news for the penguins – but researchers warn they could act as “Trojan horses” and facilitate the spread of the virus to vulnerable species.

“These asymptomatic cases may seem reassuring for the species in question, but they have strong implications for Antarctic wildlife in general, potentially leading to undetected and widespread virus transmission,” wrote researchers led by Fabiola León of UC Chile, in the bioRxiv paperthat has yet to be peer-reviewed.

Their findings are cause for “some cautious optimism for penguin populations,” says Colin Butter, associate professor of bioveterinary sciences at the University of Lincoln, who was not involved in the study.

While it is possible that some penguin populations are resistant, as with many penguin populations, this is not known for certain other penguin species have died in South America. The widespread spread of bird flu across Antarctica would also threaten other populations, including seals and whales. “The Antarctic ecosystem is precious and vulnerable. The influenza virus can cause a devastating disruption from which it will not recover,” Butter said.

Ed Hutchinson, a molecular biologist from the MRC-University of Glasgow Center for Virus Research, who was also not involved in the paper, said the limited sample meant this study only gave a snapshot of what was happening.

“The fact that apparently healthy birds were found to be infected with influenza viruses is very important, but not surprising,” he said. “We know from elsewhere in the world that some bird species are more likely to become seriously ill from this virus than others.

“As the spread of the coronavirus in humans has reminded us, the presence of healthy but infectious individuals can be a real problem in controlling the spread of an outbreak… this study highlights the importance of continued monitoring of this.”

Dr. Connor Bamford, a virologist from Queen’s University Belfast, said he was cautious about the findings. “More work is needed to study these animals in relation to bird flu in disease and health. High mortality rates associated with the highly pathogenic H5 have been documented in penguins in the past. However, the reasons why these penguins appear to be protected, and the implications thereof, are difficult to say.”

The tests between December 2023 and January 2024 were conducted along the east and west coasts of the Antarctic Peninsula and the west coast of Antarctica. It provides a snapshot of how the virus is spreading across the continent.

A total of 115 apparently healthy birds were sampled, and nine of them tested positive, including eight Adélie penguins and one Antarctic cormorant. Researchers tested 31 emperor penguins and none tested positive. It is not possible to say whether the virus has reached these colonies and is no longer present, or whether these birds have not been exposed to it at all.

Bird flu was first confirmed on the Antarctic mainland in February, following a number of cases on the sub-Antarctic islands. The paper’s researchers said: “The first detection of suspected cases of H5N1 influenza in penguins and cormorants on the Antarctic continent marks a significant expansion… into this isolated continent and endangers highly vulnerable bird populations.”

The spread of H5N1 has caused millions of wild birds to die worldwide, while thousands of sea lions and seals have also died due to ‘spillover’ events to wild mammals. Following arrival in the sub-Antarctic region in October, there have been deaths of approximately ten species of Antarctic seabirds and seals.