What is causing the spread of bird flu?

An “apocalyptic” mass mortality event that left thousands of sea lions and sea elephants dead on the coast of South America has led some California marine mammal experts to believe that a similar scene to H5N1 infections could be seen on California's Pacific coast and other continents. However, we are concerned about the possibility of this happening and are increasing our vigilance. Avian influenza continues to be rampant around the world.

Highly pathogenic avian influenza viruses have become notorious for their devastating effects on wild bird and poultry populations over the past four years, but they have not caused so many deaths in mammal populations. That was just recently.

So far, the virus's ability to jump from mammal to mammal has been limited, but the scale of infections and deaths in South America raises troubling questions about whether anything has changed.

Although it remains unclear whether this particular strain of H5N1 has improved its ability to pass easily between mammals, such a development could have potentially devastating consequences for both endangered and non-threatened species. may result in

Chris Walzer, executive director of health for the Wildlife Conservation Society, wrote in a January statement that the disease “poses an existential threat to the world's biodiversity,” and the sight of dead elephant seals ” It can only be described as apocalyptic.”

According to the Centers for Disease Control and Preventionthe H5N1 virus circulating in birds is “considered to pose a low risk to the general public in the United States. However, people who have work-related or recreational contact with infected birds may be at increased risk of infection. Appropriate precautions as outlined in CDC guidance should be taken.”

The World Health Organization also believes the risk of human-to-human transmission is low and notes that vaccine candidates are being developed to prepare for a pandemic.

But Marcela Uhart, a wildlife veterinarian at the Argentina-based One Health Institute at the University of California, Davis, said the speed with which the virus decimated once-thriving animal populations was surprising. Ta.

In November, the mortality rate of newborn elephant seal pups on a beach in Argentina reached 96%. This is astronomically higher than the 0.8% mortality rate observed there in 2022.

“It will be over in 10 days. There is nothing alive left,” Uhart said.

Deaths have also been observed in dolphins and fur seals in South America. And the virus is effectively knocking on the doorstep of Antarctica, home to more than 100 million birds and marine mammals, including penguins who live in colonies.

“Climate change and habitat destruction are taking a huge toll on the planet's wildlife species,” said Rebecca Dewar, an avian veterinarian with the International Bird Conservancy in Long Beach. “And this. It's terrible.”

In California, some experts are concerned about the vulnerability of sea lions and sea otters.

“California has been spared some of the large-scale mortality events seen elsewhere in the world. But there are still species that are highly susceptible to it. No matter how you look at it, we… We're not out of the woods,” Dewar said.

Nesting seabirds and breeding marine mammals occur throughout the California coast, Channel Islands, and Farallon Islands. Seasonal species include terns, sea lions, and sea otters.

“There remains great concern about what will happen in the big picture over time,” she says. “This summer is breeding season, a time when other parts of the world are experiencing massive population declines in breeding colonies.”

The impact is not limited to infected animals, Duer said. These animals are important within the broader ecosystem. For example, guano produced by breeding bird colonies provides nutrients for marine invertebrates and fish.

And such damage to sea otters would jeopardize the health of California's vast kelp forests, making them easy prey for sea urchins, said Kristin, a professor of epidemiology and ecosystem health at the University of California, Davis. Johnson said.

And while there aren't very large populations of marine mammals in the southern and northern hemispheres, even if there was contact, we can't really be sure of anything because the world is changing so rapidly, Johnson said.

“The distribution of marine life is largely determined by where its food goes, which itself is determined by ocean trends and warming,” Johnson said. “Based on climate or other factors, are there any species that are now redundant that didn’t exist before?”

He said factors such as climate change and habitat destruction may have influenced the geographic spread of the virus and the initial and continued understanding of wildlife.

“There is growing evidence that the frequency of pandemics, particularly those originating from wildlife, is increasing,” Johnson said. “There's not much separation or segregation between wild animals and their pathogens, and between livestock and humans.”

Until recently, highly pathogenic avian influenza (HPAI) was considered to be strictly a poultry disease. It will spread everywhere (mostly in Asia) and will be quickly suppressed by killing all the infected farm birds.

But in 2002, the virus spread to wild birds, and in 2005 it spread to Eastern Europe, infecting seven people after feathering wild swans. Four of them died. Nine years later, the disease reached North America, likely via Alaska. Birds from all over the world come to Alaska to feed during the summer. And after a brief lull in Canada and the United States, and occasional flare-ups in Asia, Europe and Africa, it came back with a vengeance in 2021.

Since then, hundreds of millions of domestic birds have been culled, as well as countless wild birds and animals infected with the virus.

Juliana Lennock, national coordinator for wildlife services at the U.S. Department of Agriculture's Animal and Plant Health Inspection Service, said scientists are awaiting genetic information from South America, but “there is no evidence of a high degree of concern yet in the United States.” . But I think looking at mammalian spillover and potential mammalian spread is what the international community is looking for. ”

The agency conducts regular bird sampling and only samples suspected mammals.

“We adopt them from state agencies or wildlife rehabilitation facilities or people with suspicious symptoms…so what we have is probably an underestimate,” she said. To tell.

But so far, the situation in North America is different from the “madness” seen in South America.

The only mammals known to scavenge for dead birds include foxes, skunks, coyotes and bears in the United States and Canada. There is no indication that a mammalian-to-mammalian pathway exists.

But North American animals may also share defenses that South American wildlife lacks.

Because the virus has been present in North America since 2014, most wildlife on the continent “has some sort of underlying immunity to influenza,” said Deborah Fauquier, a veterinarian with the National Oceanic and Atmospheric Administration. “They have some antibodies. They may not be perfect… but they've seen the virus before.”

“In South America… these people were basically naive and had never experienced a high pass (influenza) before. … So they didn't have the kind of immunity that seals and birds have. I don’t have one,” she says.

Therefore, it remains unclear whether the mass mortality of marine mammals is the result of new exposure to the disease or because the virus has acquired the ability to move between mammals.

But neither case bodes well for wildlife in the last remaining regions of the world where the disease is still undetected: Antarctica and the Oceania region, which includes Australia, New Zealand, and surrounding islands.

Woohart said she was scheduled to leave on a cruise ship to collect animal samples in Antarctica in late February. She said she would go out and conduct surveillance to make sure everything was in order before tourists were allowed to disembark from the boats for landing. She also collects samples.

“We’ve seen enough of that,” she said. “I know exactly what it's like.”

Prime Minister Boris Johnson said countries around the world needed to step up surveillance as the virus continued to spread.

As with the coronavirus that causes COVID-19, this strain of influenza is constantly evolving and changing, with new variants emerging all the time. But fatigue is beginning to set in among many governments around the world who have been battling the virus for three or four years.

“No one wants to think or talk about another pandemic,” she says. But keeping track of their whereabouts and changes is important for conservation, ecosystems, and human health.

“I think countries … need to start preparing the necessary response efforts for major biosafety concerns,” she said. “People are talking about the high death rate and the fact that there are a lot of viruses around.”