The corona pandemic has not yet been overcome, and some experts are already warning of the next danger: bird flu could bring the next deadly pandemic with it if the virus spreads to mammals and ultimately humans. But how high is the risk really?
It is undisputed that outbreaks of avian influenza have had a tremendous impact on birds in recent months and that the current outbreak is worse than previous cases. Avian influenza has now been identified in a number of mammals including cats, foxes, otters, seals and sea lions, and appears to have spread to a mink farm in Spain. A small number of human cases have also been reported.
This is undoubtedly worrying, but no reason to panic just yet. Deadly outbreaks of bird flu are, at least to some extent, man-made and controllable. The first outbreaks occurred on poultry farms, where the cramped conditions in stalls or cages provide an ideal breeding ground for viruses. “The strains of bird flu that are dominant today probably originated in poultry production,” says Alastair Ward, a wildlife biologist at the University of Leeds in England.
Prolonged outbreaks of the bird flu virus
What is less clear is how the virus moves back and forth between wild and farmed birds. So far, transmission has been observed every year mainly when migratory birds are on their migration and bring the virus from one region of the world to another and back again. Not so last year: Instead of seasonal outbreaks of the virus, there were long-lasting outbreaks, Ward says. So the virus seems to have persisted, either in the environment or in the birds themselves.
Millions of birds have died as a result. In the United States, the virus has infected more than 58 million birds since the beginning of last year. The vast majority are commercially farmed poultry, but wild birds have also been badly hit, such as the endangered Dalmatian Pelican. In 2022, the virus wiped out an estimated 10 percent of the world’s population of these birds.
Intermediate stages of propagation
The virus already appears to have undergone some sort of mutation that allows it to infect more birds, Ward says. So what speaks against a future tribe spreading from person to person?
The spread of the virus between other mammals may actually be an intermediate step between bird-to-bird and human-to-human transmission. That is why the report about a Outbreak at a mink farm in Spain alarm bells have been ringing over the past month.
There are two ways viruses can “jump” from one species to another, Ward says. First, the mammals mentioned in recent reports may have picked up the virus from infected bird carcasses. The cadavers of a group of birds that died from bird flu were “bursting with viruses,” the expert said. For example, if a fox were to eat the infected carcasses, its immune system could be overwhelmed by the virus. This could be deadly for the fox, but it would not necessarily be able to pass the virus on to another fox.
The second type of contagion would be more worrying. So far, bird flu has rarely affected humans. But viruses can mutate quickly. Different strains can inherit genetic sequences from each other that could help them survive or spread. If a new variant were better able to infect mammals — including humans — it could also spread between them, quickly hopping from one species to another. This could well be the start of another pandemic. However, there is still no conclusive evidence that this jump has taken place.
At the Spanish mink farm, 52,000 animals lived in metal cages. Wild birds in the region had recently died from the virus. It’s unclear how the virus got into the farm or how it spread among the animals. All animals have since been killed as a precaution, bringing back memories of 2020 when millions of mink were killed after scientists found a variant of SARS-CoV-2 had spread between animals and transmitted to humans.
The threat of bird flu was always there
In the current case of bird flu, fortunately, that doesn’t seem to have happened yet. None of the people working at the Spanish mink farm appeared to have contracted the virus. Only one person caught a cold and tested negative for bird flu.
But that doesn’t mean people can’t get bird flu. In the 1990s, there was an outbreak in Hong Kong that killed hundreds of people. And over the past year, single people have tested positive for the virus, including a man in England who kept 20 ducks in his home and a person in the US involved in industrial chick shredding.
But at least as far as people are concerned, not much has changed in the past year. There is no new convincing evidence that avian influenza is more likely to cause a human pandemic now than it has been in previous years. There is therefore no reason to panic. Not yet.
(jle)
