The global bird flu wave has now jumped to mammals in the UK, including otters and foxes, a new study has found.
The discovery was made after employees at the UK's Animal and Plant Health Agency (Apha) tested 66 mammals for avian flu. Nine otters and foxes were found to be infected.
British officials are now carrying out more targeted testing and surveillance in animals and humans exposed to the virus, known as H5N1.
Bird flu has wiped out tens of millions of birds in Europe in the past year. Many of the birds were slaughtered to stop the disease from spreading.
Worldwide, the disease has also been discovered in grizzly bears, mink and even a dolphin.
Experts have stressed the risk to humans is low, but acknowledge there is a possibility it could one day jump to people.
“These animals, these are wild mammals, animals that scavenge on sick and dead birds. And there is a lot of dead wild birds at the moment due to the bird flu presence around the globe,” Professor Ian Brown, scientific services director at the Animal and Plant Health Agency (Apha) told Radio 4’s Today show on Thursday.
“We have to be watchful, which is why we are enhancing our surveillance in the UK, to make sure we can track and monitor for these changes.
“So Defra, the devolved administration, are supporting a programme to actively look in animals that we believe might scavenge on wild birds. We analyse those viruses if we detect them and we share that information very rapidly with our public health counterparts, so we can make a clear and rapid assessment."
He said there is no evidence of transmission from fox to fox or otter to otter, making them what is called “dead end infections”.
Asked about whether the Apha is asking questions about whether it could spread to humans, he said: "Yes and that’s what we’re looking for, that’s why we’re doing the work. We need to understand the consequence of this infection. Does it make the virus change by jumping its host? We’re aware those events can sometimes lead to that.”
But Prof Brown said the world is a long way from the current avian flu outbreak – the worst in history – becoming a pandemic among humans, which would require a change in the genetic code of the virus.
But we need to still be watchful, he said.
In November, officials in the UK instructed all poultry and captive birds in England to be kept indoors in an effort to prevent the spread of the virus.
Hundreds of cases have been confirmed on commercial premises, smallholdings and in pet birds since October last year.
Last week a domestic cat was euthanised after suffering from severe neurological symptoms due to a case of bird flu it picked up from a nearby poultry farm that raised ducks.
And scientists from Dagestan State University are currently investigating whether the mass death of 700 seals found dead in December in the Caspian Sea is related to the virus, which was found in wild birds there months earlier.
If confirmed, it would make it the first event of mammal to mammal transmission of the virus.
"If this turns out to be sustained transmission in a wild mammalian species this is yet another worrying ‘first’ with these H5N1s that shouldn’t be ignored," Dr Tom Peacock, a virologist at Imperial College London, told The i newspaper.
“It would be yet more evidence these H5N1s could be poised to cause the next pandemic.”
Since the outbreak began a year ago, fewer than 10 people have caught the virus, and only directly from birds via close contact. One person has died.
However, scientists have warned they have seen changes in the virus from samples from a mink farm in Spain which could more easily replicate in mammalian tissue.
More than 200 million birds have died or had to be culled since the onset of the outbreak.