The bird flu virus circulating in East Anglia has spread into wild mammals including foxes and otters - heightening fears over its potential to infect humans and their pets.
East Anglia has become a national epicentre for the epidemic which has decimated wild bird colonies and poultry farms.
But there is now evidence that the virus has jumped into UK mammals too.
The Animal and Plant Health Agency (APHA) has tested 66 mammals and found nine otters and foxes tested positive for the highly pathogenic H5N1 strain of avian influenza.
It is believed they had eaten dead or sick infected wild birds.
The UK Health Security Agency warned the mutation in mammals "may imply this virus has a propensity to cause zoonotic infections", meaning it could potentially infect humans - but currently there is "no evidence of sustained human-to-human transmission".
Paul Hunter is a professor in medicine at the UEA, and an expert in viral diseases.
He described the risk of a human bird flu pandemic as "low probability, high impact" - meaning that although it is unlikely, it could be "dreadful" if it happened.
"It is worrying, but I don't think we should get too scared at the moment," he said. "Avian flu does not jump easily into mammals or humans.
"But we need to keep a check on this and if it ever does look like spreading in humans we need to make sure we have got vaccines up and running very quickly.
"It is a big leap for a virus to be infectious in birds to being infectious in humans. It is less of a leap for it to be in mammals and then spread to humans.
"Normally we don't come into contact with animals like foxes, so the risk of human transmission is very low, but it is possible foxes could spread the infection to a family dog and that then takes it into someone's home.
"So if you are out walking with the dog - or indeed your children - and they find a dead bird, for God's sake don't touch it, get them away from it."
Prof Hunter said there was a warning from history in the devastating Spanish Flu of 1918, believed to have begun as an avian influenza which eventually infected pigs, and then humans.
Since October 2021, when the latest outbreak began, the World Health Organisation (WHO) says there have been five confirmed human cases of the H5N1 virus, including one in the UK, and one death, in China.
A recent WHO report says while poultry farming carries a risk of "small clusters of human cases", the virus has "not acquired the ability for sustained transmission among humans".
The public is warned not to touch dead or sick birds, but to report any dead birds of prey, three or more dead wild waterfowl or five or more dead birds of any species to the Defra helpline 03459 335 577 or online at www.gov.uk/guidance/report-dead-wild-birds.
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