2023-05-12 15:28:47
Outbreaks of bird flu were always limited to autumn and winter. Migratory waterfowl brought the virus here. It would go around violently for a few weeks or months, but then the disease would die out again. But the variant that is now circulating has been more or less permanently present since the fall of 2020.
“Now you see that black-headed gulls are severely affected in the previously quiet spring,” says Rotterdam virologist Thijs Kuiken. “The virus has adapted and is spreading much faster among wild birds. As a result, it does not disappear after the winter.”
This variant has now spread all over the globe, outbreaks are occurring more often and such an outbreak usually involves much larger numbers. The virus is no longer going away from nature. Some bird species, which are already struggling, are under serious threat, such as the California condor or, in Europe, the peregrine falcon and the sandwich tern.
Humans can also become infected
Dozens of mammal species are also infected, especially animals that hunt birds. In the Netherlands these are, for example, foxes, stone martens and polecats. Mammals rarely pass the virus on to each other. Kuiken is aware of two examples where transmission cannot be ruled out: at a sea lion colony off the coast of Peru and at a mink farm in Spain.
Humans are also infected with this so-called highly pathogenic variant. Officially, there are about a thousand cases, mainly in China. There may be more because of underreporting. The disease is not very contagious, people rarely pass the virus on to each other, but it is dangerous. Of those thousand people, half have died.
In the meantime, it seems only a matter of time before the virus acquires the mutations that allow mammals, including humans, to pass it on to each other. Chick points to a greater danger. Pigs have so far been spared this virus, but they are notorious mixing vessels of flu viruses. If a pig becomes infected, the bird flu virus can cross with a pig virus and a new variant that is contagious to humans can arise. “That is exactly how the 2009 pandemic flu originated.”
Expert advice is hardly followed
It is not for nothing that the Experts Council-Zoonoses, an advisory body that keeps a finger on the pulse of diseases that can be transmitted from animals to humans, recently considered it undesirable to keep pigs and poultry at the same location. Kuiken notes an advice that RIVM also issued in 2008.
The same expert council advises to reduce the poultry density in the Gelderse Vallei, not to keep chickens or ducks in areas rich in waterfowl and to vaccinate poultry. It’s not really happening yet, even though there have been successful trials of commercially available vaccines, which were found to protect poultry and reduce virus shedding.
Kuiken is non-committal about why, but he cannot come up with a convincing argument against vaccination. “Earlier objections have been superseded. We can now see whether a chicken is vaccinated or infected. We know how to prevent vaccinated animals from spreading the virus.”
The only thing that happens now is preventive clearing. More than 6.6 million largely healthy chickens have been killed in the Netherlands since October 2021. That would no longer be necessary with vaccinations, says Kuiken. “But vaccination does not prevent mortality among wild birds. And the threat that the virus will still be able to make the transition to humans somewhere in the world remains present.”
Read also:
What is the chance that the avian flu virus will also become a danger to humans?
The H5N1 virus is rampant in the avian world and regularly crosses over to mammals. A Spanish mink farm was recently hit. What is the chance that the virus will become contagious to humans? No idea, says virologist Ron Fouchier. “But this outbreak should wake us up.”
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