Bird flu infections have been reported in several mammals, including foxes and minks. However, it is still unclear whether the virus can also be transmitted from one mammal to another.
The world is in the midst of the largest bird flu outbreak ever. Currently, mammals are also being infected. How much should we be concerned?
What is the current situation?
Since October 2021, when the latest outbreak began, the H5N1 subtype of the virus has spread through seabird colonies, poultry and wild bird flocks in the US, Europe and beyond. Worldwide, about 15 million domestic birds have died from bird flu in the past 15 months, and more than 193 million birds have been culled to prevent the virus from spreading to other birds.
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The only thing authorities can do to limit the spread is to keep poultry away from wild populations. Since November 2022, all UK poultry, including free-range, must be kept indoors until further notice.
Does the outbreak also occur in mammals?
The virus has been found in a variety of mammal species: from foxes in England to minks in Spain, grizzly bears in the US and seals in the Caspian Sea. The World Organization for Animal Health (WOAH) told the BBC that there have been 119 mammalian bird flu outbreaks recorded, with about 200 individual cases.
There have been outbreaks in otters and foxes in the UK, according to statistics from the Animal and Plant Health Agency (APHA). In 2021, 49 mammal carcasses infected with bird flu were collected, in 2022 there were 119 and this year already four.
Do we have a full picture of what is happening?
The WOAH warns that the number of infections in mammals is likely to be underestimated because it is difficult to study wildlife on different continents. It is unclear whether mammals always get the virus directly from birds, or whether it spreads between mammals.
Studies by Wageningen Bioveterinary Research show that there is no spread of the H5N1 virus between wild mammals such as foxes. There is evidence that these animals became infected independently from eating contaminated wild birds.
“What we don’t have evidence for is that it can go from fox to fox or from otter to otter. So these are what we call dead-end infections,” said APHA’s Ian Brown on February 2 BBC Radio 4.
But the DNA of the virus of an outbreak in October 2022 on a mink farm in Spain does suggest that the animals were infected with a new variant of H5N1 that can spread among minks. It is also being investigated whether an outbreak that killed more than 700 seals in the Caspian Sea in December 2022 provides evidence of mammal-to-mammal transmission, said the newspaper i news.
More research is needed before mammal-to-mammal transmission can be confirmed, he says Munir Iqbal from the Pirbright Institute in the United Kingdom. The virus in the mink farm could have spread through a contaminated water source or feed, he says. “If one animal is infected and they all share the same water, the contamination is probably through the water,” he says.
Can humans get bird flu?
People can get bird flu, although it is rare. Over the past 20 years, there have been nearly 870 cases of human infection with H5N1 in various outbreaks, 457 of which have been fatal, according to the World Health Organization WHO.
Symptoms include fever, muscle aches, headache, and cough or shortness of breath. People who come into close contact with infected birds are at greatest risk. It is therefore advised to avoid close contact with wild birds and poultry. There is currently no evidence that the avian flu virus can be transmitted between humans.
Researchers do fear that if the H5N1 virus mutates to jump from mammal to mammal, it could also happen between humans. “If the virus is able to move between wild animals, that means the virus can persist in those animals,” says Iqbal. “And if the virus adapts to mammalian species, that increases the risks for humans.”