Bird flu is decimating wildlife around the world and is now spreading in cows. In the handful of human cases seen so far it has been extremely deadly.
The tips of Lineke Begeman’s fingers are still numb from a gruelling mission. In March, the veterinary pathologist was part of an international expedition to Antarctica’s Northern Weddell Sea, studying the spread of High Pathogenic Avian Influenza (HPAI), the virus that has now encircled the globe, causing the disease known as bird flu.
Cutting into the frozen bodies of wild birds that the team collected, Begeman was able to help establish whether they had died from the disease. The conditions were harsh and the location remote, far from her usual base at the Erasmus Medical Centre in the Netherlands. But systematic monitoring like this could provide a vital warning for the rest of the world.
“If we don’t study the extent of its spread now, then we can’t let people know what the consequences are of having let it slip through our fingers when it began,” Begeman tells BBC Future Planet. “I imagine the virus as an explorer going through the world, to new places and bird species, and we’re following it along.”
Relatively few people have caught the virus so far, but it has had a high mortality rate in those that do: more than 50% of people known to become infected have died.
Moreover, the impact on animals has already been devastating. Since it was first identified, the H5 strain of avian influenza and its variants have led to the slaughter of over half a billion farmed birds. Wild-bird deaths are estimated in the millions, with around 600,000 in South America since 2023 alone – and both numbers potentially far higher due to the difficulties of monitoring. At least 26 species of mammals have also been infected.
In Antarctica’s Northern Weddell Sea, Begeman and her team sampled around 120 carcasses from different species, including several Antarctic fur seals. The virus was detected at four of the 10 sites they visited.
It was not the first time bird flu had been detected on this remote continent. That first case was a month prior, in February 2024. But theirs was the first confirmation from this particular region, and the first time, Begeman believes, that a multidisciplinary team had set out to systematically determine its Antarctic spread.
“The moment we found the first evidence of that destructive serial killer virus amidst such a bird-rich, pristine area, we realised what disaster is about to happen and it became sickening indeed,” says Begeman.
Already the worst bird flu outbreak in wildlife on record, scientists like Begeman are now racing to track its journey – and so better understand how its further spread among humans might be stopped.
Where does bird flu come from?
China’s southern Guangdong region is a mosaic of lakes, rivers and wetlands. These watery habitats are well suited to aquatic birds, who are natural hosts for low pathogenic avian flu. And it was here, in 1996, that a farmed goose became the world’s first bird to be diagnosed with a new, highly pathogenic strain of the virus, known as H5N1.
The categorisation of bird flu as low or high pathogenic was established in relation only to chickens, not to other bird (or mammal) species. But whereas low-path avian influenza is non-fatal in wild birds and only causes mild disease in chickens, in poultry, low path strains can mutate into fatal high-path ones, causing severe illness and often death.
People are the real problem – Thijs Kuiken
It should be no surprise that the highly pathogenic virus’s first case was detected on a poultry farm, says Thijs Kuiken, a comparative pathologist at Erasmus University Medical Centre in the Netherlands. “High pathogenic avian influenza is typically a poultry disease, which doesn’t occur in the wild. What’s unusual now, is this particular type has spilled into wild birds and this has allowed it to spread worldwide.”
Although wild birds have now helped the virus reach far beyond China, “people are the real problem”, Kuiken warns. And in particular, humanity’s ever-rising demand for farmed meat.
When this outbreak started in 1996, there were around 14.7 billion poultry birds in the world, mostly chickens. Now there’s double that number. “Biomass-wise, poultry currently forms over 70% of all avian biomass worldwide,” Kuiken notes.)
If the current poultry farming trends don’t change, then “other highly infectious pathogens will continue to spread into the few wild birds remaining,” Kuiken says. House finches, for instance, are proving particularly susceptible to a bacterial poultry disease, Mycoplasma gallisepticum. Virulent strains of Newcastle disease are also crossing over into multiple species, including parrots and macaws. “HPAI [high-pathogenic bird flu] is only one threat.”
How did bird flu spread around the world?
By 2005-06 the virus had spilled over into wild birds and was travelling as far as Europe, Africa and the Middle East, but it was disappearing in these populations after only a few months – likely a combination of not spreading well enough in wild birds, not surviving well enough in water, and some birds developing immunity, says
That relative containment changed in 2020, however, when a new strain of H5N1 emerged. Though it’s not known exactly why, the strain could maintain itself in wild bird populations year-round. Now able to spread during springtime when birds gather in high densities to breed, the virus rapidly became endemic in wild bird populations.
In late 2021, the virus arrived in the New World via Canada’s eastern Newfoundland province. A black-backed gull, found sick in a pond, was taken to a wildlife rehabilitation centre where it died the following day. It was later found to be positive for H5N1. Days after its death, a poultry farm started reporting increased mortality rates and autopsies also confirmed presence of the virus.
The fact there was no evidence this farm had imported poultry from Europe helped to confirm scientists’ theories that wild birds’ migration routes are the key long-distance carrier, explains Kuiken. There have been some exceptions, however, such as the transport of infected turkeys from the UK to Europe.
Source: BBC
It’s like avoiding getting into a packed metro when you’re already sick – Gregorio Torres
By 2022, birds in colonies from the UK to Israel were dying in their thousands. In October 2022, the virus was detected in wild birds on the west coast of Peru and Chile. After travelling down the coast, it then returned up the east, spreading to the Falkland Islands and South Georgia – the stepping stones to the Antarctic.
Along this route, the virus has diverged to infect a wide variety of mammals – including 21 species in the US alone. And with such cross-over, the opportunity for both human contact and mammal-to-mammal spread has increased.
By 16 April 2024, HPAI was confirmed in dairy cows on 26 farms in the US, from Texas to Michigan. Some of these may have been infected through wild birds, but other cases have been connected to cows’ long-distance transport. So far, only one case of cow-to-human infection is thought to have occurred, and the virus may require several more mutations beforeit can spread easily between people.
But farms can create conditions that allow disease to spread more easily, offering new pathways for adaptation. “Wild birds can transmit the virus, but domestic farms can amplify it,” says Gregorio Torres, head of the science department at the intergovernmental body the World Organisation for Animal Health, of the need for farmers to be especially cautious. “It’s like avoiding getting into a packed metro when you’re already sick.”
One bright spot is that birds in New Zealand and Australia have so far been spared. The countries are part of the East Asian-Australian migration route, but their visiting birds are mostly shorebirds or waders, rather than more-susceptible waterfowl like ducks or geese, Kuiken notes.
Source: BBC
Quote
By 2005-06 the virus had spilled over into wild birds and was travelling as far as Europe, Africa and the Middle East, but it was disappearing in these populations after only a few months – likely a combination of not spreading well enough in wild birds, not surviving well enough in water, and some birds developing immunity, says
That relative containment changed in 2020, however, when a new strain of H5N1 emerged. Though it’s not known exactly why, the strain could maintain itself in wild bird populations year-round. Now able to spread during springtime when birds gather in high densities to breed, the virus rapidly became endemic in wild bird populations.
In late 2021, the virus arrived in the New World via Canada’s eastern Newfoundland province. A black-backed gull, found sick in a pond, was taken to a wildlife rehabilitation centre where it died the following day. It was later found to be positive for H5N1. Days after its death, a poultry farm started reporting increased mortality rates and autopsies also confirmed presence of the virus.
Getty Images
