Since January, hundreds of dead or dying sea lions have washed up on Peru’s beaches.
Before they died, the animals – majestic predators that can weigh up to 350 kilos – suffered from agonizing convulsions and struggled to swim.
Nothing like this had ever been observed in the region.
A scientific team of Peruvian and Argentine researchers has now confirmed that the mass deaths of the sea lions are due to the avian influenza A(H5N1) virus, which has jumped from seabirds to these wild mammals.
The researchers do not rule out a frightening hypothesis: that the virus may have learned to spread from mammal to mammal, as apparently happened at a Spanish mink farm.
It would be the first time this has occurred in nature.
In Peru, a total of 634 sea lions have been found dead.
The prevailing theory is that the mammals became infected individually and independently by cohabiting with sick birds or eating their carcasses, according to Argentine biologist Sergio Lambertucci, one of the investigation’s leaders.
However, the scientist points to a worrying incident on January 27, when a hundred dead sea lions were found in the waters of Isla Asia, less than 100 kilometers south of Lima, Peru’s capital.
“It wouldn’t be surprising if some of them had eaten infected birds, but all of them?” said Lambertucci, who works at the Biodiversity and Environment Research Institute in the Argentine city of San Carlos de Bariloche.
Dutch veterinarian Thijs Kuiken, an expert on emerging diseases, is also skeptical of the hypothesis that each sea lion was infected individually.
“Given the large number of specimens found dead, it seems more likely that there was direct transmission between sea lions,” says Kuiken of Erasmus University Medical Center in Rotterdam.
“This is worrying,” he continues. “This is the second case of mass mortality, suggesting that the virus can easily adapt to efficient mammal-to-mammal transmission. If it can occur in mink and sea lions, why shouldn’t it occur in humans?”
The A(H5N1) virus circulating worldwide is a highly pathogenic avian influenza subtype.
It has caused the most devastating epidemic in history in Europe, killing more than 50 million poultry in just one year.
In late 2022, the virus reached South America and wreaked havoc in Peru, where it killed more than 50,000 wild birds, mostly pelicans, and boobies, according to Peruvian and Argentine scientists.
The pathogen has already jumped from birds to mammals and, in exceptional cases, even to humans on several occasions. In those cases, however, there was no mammal-to-mammal transmission.
Scientists fear the virus could mutate and cause a deadly pandemic in humans.
Thijs Kuiken cites another cause for concern:
“There is video footage of people in Peru trying to rescue sea lions that may be infected with the virus. This close contact increases the likelihood of the virus being transmitted from sea lions to humans.”
The Peruvian government has urged citizens not to approach wild animals.
On Jan. 3, a nine-year-old girl from Ecuador who had contact with backyard poultry was admitted to the intensive care unit in critical condition after contracting the A(H5) virus.
According to the World Health Organization, the girl recovered from the virus.
It was the first reported case of a human being infected with this strain of the avian flu virus in Latin America.
In Peru, 634 dead sea lions were found on various beaches and in protected areas of the country, such as the Paracas National Reserve.
The researchers analyzed six specimens and found the virus in all of them.
Autopsies of other specimens also revealed traces of avian influenza, namely hemorrhagic pneumonia in the lungs and hemorrhagic encephalitis in the brain.
Lambertucci points out that sea lions are very social animals that live in crowded colonies.
“When you think about wildlife species that are most likely to have mammal-to-mammal transmission, they are social animals like sea lions that live very close together,” Lambertucci says.
Before publishing their findings on the sea lions, the Peruvian and Argentine scientists had warned that the arrival of the avian flu virus posed a threat to protected birds in South America, including the Andean condor.
In light of the mass deaths among sea lions, the researchers decided to immediately publish the first draft of their study on these mammals without waiting to finalize it.
“We wanted to sound the alarm as soon as possible, given the worrying situation. This is the first case of mass mortality in wild mammals in South America and could be the first event of intra-species transmission in wild mammals worldwide,” explains Lambertucci.
The Argentine biologist stresses that they will have to conduct genetic studies of the virus to confirm or refute their hypotheses – work that will take weeks.