UK officials are now testing mammals for avian influenza (bird flu) and have reported evidence of a “direct spillover from birds into some scavenger wild mammalian species”.

In 2022, 56 mammals were tested, of which eight were positive, the UK Health Security Agency (HSA) said in its most recent impact assessment.

“Enhanced” mammalian surveillance was initiated at the beginning of this year, targeting mammals found dead near known areas of bird flu transmission and, so far, two animals have been tested, of which one fox was positive.

It is presumed that foxes affected – and otters, the HSA notes – have or had “direct high-level exposure to infected birds based on feeding behaviour and food preferences”.


The strains of bird flu found in the positive mammals are so far different from what is most common in birds (H5N1).

“The four available influenza genomes from these positive mammals all show the PB2 E627K substitution,” the HSA explained.

This mutation is known to be acquired rapidly after infection of a mammalian host in some flu viruses and is associated with enhanced replication. 

“The rapid and consistent acquisition of the PB2 mutation in mammals may imply this virus has a propensity to cause zoonotic infections and further assessment should be made of the properties of this mutation,” the HSA added.

There have also been confirmed infections in mammals in other countries according to the impact assessment, including “multiple species in the US, a cat in France, and a large outbreak in farmed mink in Spain”.

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The mink affected in Spain had a different a PB2 mutation to that seen in UK mammals and its transmission is of “significant concern” to the HSA.

In a report of the Spanish mink outbreak in the scienctific journal Eurosurveillance, researchers said: “The viruses detected at the mink farm are distinguished from all the clade H5N1 viruses characterised thus far in the avian population in Europe as they bear an uncommon mutation (T271A) in the PB2 gene, which may have public health implications.”

However, the HSA assessment added that there is no clear evidence that this has continued in mammalian species since the initial outbreak, which was in October 2022, nor does Animal and Plant Health Agency data (APHA) suggest “widespread mammalian adaption” of the virus.

Furthermore, the HSA assessment believes that there are no indicators of increased risk to human health at present. The agency will continue to review the assessment regularly.

In the UK, there have been 166 confirmed cases of bird flu – the H5N1 strain – since October 2022, and 279 since the H5N1 outbreak started in October 2021.