Forgotten epidemic: How is the bird flu outbreak evolving now that more than 280 million birds have died?
With at least 280 million birds dead since October 2021, the highly contagious H5N1 strain of bird flu has devastated the poultry industry and caused the largest sudden decline in the world’s wild bird population in decades. The millions of wild birds killed include tens of thousands of endangered and endemic species – and tens of thousands of mammals have also died.
Today, new datapublished in Nature Communications, documents the spread of the disease to the southernmost tip of the planet – the Antarctic region – where it has caused significant mortality among elephant seals and fur seals. This outbreak has affected every continent except Oceania, and yet little attention has been paid to its impact on global biodiversity and agricultural systems – or to potential risks to human health.
“I’m not sure the public is aware of the significance of bird flu,” said lead author Prof Ashley Banyard, a virologist at the UK’s Animal and Plant Health Agency (APHA) lab in Weybridge, Surrey. “It hasn’t been front-page news.”
Experts are doing everything they can to learn more about the disease and understand how it will develop further. ““We can’t rest on our laurels … we have to make sure that we’re constantly monitoring and tracking the threat of avian influenza viruses,” Banyard said. “It’s almost impossible for me to predict what’s going to flare up where.”
Dr Connor Bamford, assistant professor of virology at Queen’s University Belfast, said there could be more surprises to come. “A big open space for the virus remains the human population.”
How did it start?
The bird flu strain that caused these deaths is more than a quarter century old. The highly pathogenic H5N1 was first reported in China in 1996, when it was found on a goose farm. The origins of all highly pathogenic bird flu strains – the strains that cause severe illness and death – can be traced to poultry farms.
“The history of (bird flu strain) 2.3.4.4b goes back before we started seeing these mass die-offs of wild birds,” Bamford said. “But something seemed to happen in 2021.” That’s when the strain became the dominant bird flu virus globally and is now highly pathogenic and highly contagious.
What does an outbreak look like?
Ornithologist Peter Stronach was one of the first people in the UK to witness the unfolding breeding bird disaster. On May 11, 2022, he was walking along the beach at Littleferry in Scotland, a walk he often takes, watching for birds flying overhead. But that day was different: “There were just dead bodies of birds strewn along the tide line,” he said.
In all, Stronach counted 72 dead birds, including puffins, guillemots and great skuas. The virus had killed birds of 17 different species, the first time multiple species had been killed in the summer (rather than wintering species). “That’s really unusual. It indicated something was wrong,” he said.
As the season progressed, “everything escalated,” Stronach said. Fishermen were reporting bird carcasses far out at sea. “By doing some primitive math, we figured out that these were huge numbers and no one was watching.”
Tens of thousands of seabirds would die in the coming months. The virus survived the summer in Europe and spread rapidly worldwide, along bird migration routes.
What is the toll?
Avian influenza has caused the most significant and sudden loss of birds in decades, with some of the world’s long-lived seabird species likely to take years to recover. It has led to the deaths and mass slaughter of more than 280 million poultry birds since October 2021, according to data from the World Animal Health Information System. There is no total figure for wild bird deaths, although it is estimated to be in the millions.
It has been particularly destructive to bird species with narrow geographical ranges. The first major outbreak in the winter of 2021 was among barnacle geese in Spitsbergen’s Solway Firth, where at least 13,000 birds died: a third of the world’s population of that species. In March 2022, more than 2,200 Dalmatian pelicans have died in Greece, or 40% of the population in southeastern Europe. The United Kingdom, home to the largest breeding pairs of the great skua, has lost three-quarters of the birds at sites surveyed since bird flu struck, according to a study published in February. Across Europe, more than 20,000 Sandwich terns died during the 2022 breeding season – or 17% of the population in northwestern Europe – in an outbreak that killed almost all chicks within colonies. In total, it has killed birds from 320 speciesand mammals of dozens of species.
How does it spread?
One bird can infect as many as 100, with the virus present in feces, mucus, blood and saliva. A teaspoon of feces is enough to kill a houseful of chickens or turkeys, experts say, with mortality rates as high as 100 percent.
Where was it found?
Australia and New Zealand are the only places still free of outbreaks in wild birds. In November 2021, the first case in North America was recorded in Newfoundland, Canada, probably transmitted by a bird that came from northwestern Europe along the East Atlantic flight path. Mid 2022, more than 230 outbreaks had been identified in wild animals and had spread across Canada and the US.
In October 2022, it arrived in South America. Data suggests there were three separate introductions. It spread across the length of the continent (6,000 km) in less than six months, arriving in Tierra del Fuego in April 2023In total, more than 500,000 wild birds have died in South America.
In October 2023, bird flu arrived on the sub-Antarctic island of South Georgia. In total, it has killed animals from about 10 species in the Antarctic region (most on South Georgia), including fur seals, elephant seals and gentoo penguins.
Researchers warned of large geographical ‘black boxes’ where it is not known whether bird flu occurs in wild populations, particularly in parts of Africa and Asia.
“It’s pretty unclear what happened in Asia and Africa. If you look, it’s there, but it’s not well-recorded,” Bamford said.
There are endemic strains in Bangladesh And Cambodia. Japan has recorded recent cases in crows with large beaks; South Korea has reported it in wild swansStudies from West and South Africa confirm fallen there: since January 2022, Burkina Faso has 133 outbreaksincluding three in wild birds. Early 2023, thousands of seabirds die were observed in Senegal, Gambia and Guinea-Bissau, including Caspian Terns, Royal Terns and Grey-headed Gulls.
And what about other animals?
In South America, bird flu caused mass deaths among mammals. More than 20,000 South American sea lions died in Chile and Peru, which 9% of the regional populationAn estimated 17,000 baby elephant seals have died in Argentina, which is equivalent to 96% of all puppies born in the country in 2023. This represents the loss of almost an entire generation of seals, which take at least three years to reach maturity.
In March This year, bird flu began spreading among American cattle. It is the first time that avian flu virus has been detected in cows, with more than 100 herds affected and likely more not yet reported.
Poultry farms near farms have also reported cases, suggesting the virus may be flowing back to birds. Barn cats and mice have also tested positive for H5N1, so that they could spread the virus from the farms to the rest of the environment.
What is the risk for people?
As the virus evolves, it could become a greater threat to humans, a recent report said. report by the U.S. Centers for Disease Control and Prevention (CDC). There have been nine cases of H5N1 in humans in the U.S. (though the symptoms have been relatively mild), and officials said they expected more. “The more infections there are in cows, the greater the risk of infections occurring in humans,” said Dr. Nirav Shah, deputy director of the CDC.
The UN health agency’s chief scientist has also said the risk of bird flu spreading to humans is a “huge concern.” So far, there is no evidence that H5N1 spreads between people. But in the hundreds of cases where people have been infected through contact with animals over the past 20 years, the fatality rate has been above 50%.
What now?
In October 2023, bird flu arrived in the Antarctic region. Researchers on the ground have counted hundreds of dead seal carcasses in South Georgia. But it’s a large area with few eyes on the ground.
“It could be that the numbers we detect are only a fraction of the number that actually died,” said Norman Ratcliffe, an avian ecologist with the British Antarctic Survey (BAS) who has studied penguins and seabirds on South Georgia.
While it has killed gentoo and king penguins, the losses among penguins have been relatively small. “There is reason to be optimistic. It’s not as bad as we thought when we first saw cases,” Ratcliffe said.
In general, viruses evolve in a way that means they don’t kill their hosts – they generally become less dangerous and more infectious over time. The virus has also traveled around the world, so it has little new territory to cover – apart from Oceania.
“Predicting the future of the highly pathogenic avian influenza virus is one of the biggest challenges for the field,” Bamford said. “It is possible that this season will be less affected by a build-up of immunity in wild birds that have been infected and survived previous seasons. However, we continue to detect the virus sporadically in European birds, so we should expect more outbreaks.”