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Bird flu has jumped to mammals in the UK - so how worried should humans be?

Bird flu has been creeping slowly closer to home since the outbreak started in October 2021.

First there were the headlines about poultry being culled, then the shortage of Christmas turkeys and the barren supermarket shelves where eggs were once stacked high.

Now bird flu has spilled to mammals in the UK, with otters and foxes testing positive for the virus.

With COVID now in its fourth year, people are naturally alert to the possibility of another pandemic sweeping through the population.

Bird flu isn't about to become the next Omicron, but the possibility of the virus mutating means scientists are keeping a watchful eye.

What animals has bird flu been found in?

On Thursday, the Animal and Plant Health Agency (APHA) confirmed five foxes and four otters have tested positive for avian flu in England, Scotland and Wales since 2021.

The UK isn't alone in seeing the virus crop up in mammals. Around the world it's been found in domestic cats, grizzly bears, dolphins, leopards and more, according to the United Nations Food and Agriculture Organisation.

In October last year, mink started dying at a farm in Spain. Testing revealed they had H5N1 avian flu.

How worried should we be about bird flu in mammals?

The spread at the mink farm set alarm bells ringing. In most cases where mammals become ill - including the otters and foxes in the UK - it's likely because they ate infected dead wild birds or their droppings.

But at the mink farm, the virus appeared to spread between the animals, from pen to pen.

Genetic sequencing showed the mink were infected with a new variant of H5N1 which includes a genetic change that means animal-flu viruses are better able to reproduce in mammals, according to a report by Nature.

A UKHSA risk assessment from January concluded the apparent transmission between mink was of "significant concern" but said there was no "clear evidence" this had happened in any other species of mammal.

When it comes to the strain found in mammals in the UK, there's "currently no reason to suspect that the jump is due to a change in the virus's genetic make-up", according to Dr Alastair Ward, associate professor of biodiversity and ecosystem management at the University of Leeds.

He said foxes and otters are known to scavenge, and it's likely the bird carcasses would have had high viral loads.

"Such high exposure is likely to have overwhelmed the mammal's immune system, resulting in infection," he said.

What does this mean for humans?

Just because bird flu has been found in mammals, it doesn't mean humans are next in line.

As Dr Ward points out: "Humans rarely come into contact with wild foxes or otters, and potentially infectious contact is likely to be rarer still."

Professor Ian Jones, virologist at the University of Reading, said while the jump to different species provides an opportunity for the virus to adapt to mammals, "the natural barriers to this occurring are quite high".

"The risk to people right now therefore appears no more than it is for direct spread from infected birds."

But low risk doesn't mean no risk

The kicker is that phrase "right now". The Pirbright Institute, which carries out research into viral diseases in animals, warns that new avian flu virus strains are created frequently, meaning there is "a constant risk that one of the new strains may spread easily among people".

If this happened, we could be facing a new influenza virus pandemic.

It notes the viruses responsible for all four of the worldwide human influenza pandemics seen in the last 100 years have originated from birds.

What's being done?

The APHA is boosting its surveillance programme to make sure it tracks any instances of the virus passing from mammal to mammal.

Speaking on BBC Radio 4's Today programme, Prof Jones said Defra and the devolved administrations are supporting a programme for actively looking for mammals that we believe might scavenge and feed on wild birds.

"We analyse those viruses if we detect them, and we share that data very rapidly with our public health counterparts, so we can make clear and rapid assessments."

He added: "If you analyse the genetic code of the virus, you can work out whether it's come from a bird or whether it's going from one mammal to another."