Avian flu surveillance has been stepped up in the UK after at least 200 cases of infection in mammals were detected.
Public health experts say the risk of jumping to humans is still very low, but that risk will be monitored through increased genomic surveillance and targeted testing of people exposed to the virus. Recent outbreaks of avian flu at mink farms in Spain and mass deaths of seals in the Caspian Sea have also raised concern, possibly linked to the infection.
“The virus is fully on the march,” Prof Ian Brown, director of scientific services at the Animal and Plant Health Agency (EFA), told the BBC.
He added that experts are “intensely aware” of the risks of avian flu becoming a pandemic like Covid-19. “This global spread is a concern,” he said. “We need globally to look at new strategies, those international partnerships, to get on top of this disease.”
Over the past two years, the UK has faced its biggest outbreak of avian influenza since October 2021, with more than 300 cases confirmed and poultry farms currently required to keep birds indoors.
Figures reported by the BBC show that the virus has killed around 208 million birds worldwide and at least 200 recorded cases in mammals. In the UK, Apha tested 66 mammals, including seals, and found nine otters and foxes positive for highly pathogenic avian influenza (HPAI) H5N1.
Cases have been found in Durham, Cheshire and Cornwall in England; Powys in Wales; Shetland, Inner Hebrides and Fife, Scotland.
It is believed that the animals fed on dead or sick wild birds infected with the virus.
“The affected species – foxes and otters – are known to scavenge,” said Dr Alastair Ward of the University of Leeds. “Possibly, affected individuals have scavenged carcasses of infected wild birds, which may have very high viral loads. Such high exposure is likely to overwhelm the mammalian immune system, leading to infection.”
There is no reason to suspect that the jump is due to changes in the genetic make-up of the virus or that humans are at greater risk from infected foxes or otters than birds. However, scientists believe that close monitoring is needed to detect any mutations that could cause a jump between species. And reports of an apparent spread of the virus among mammals on mink farms and the possibility of an outbreak in wild seal populations have raised concerns.
Professor Ian Jones, a virologist at the University of Reading, said: “While these constant attacks of viruses on mammalian species provide opportunities for the virus to transfer to mammals, the natural barriers to this are very high and there is no problem. A sign of dispersal within these species. So now the risk to humans appears to be greater than direct transmission from infected birds.”
In a recent report, the UK Health Security Agency (UKHSA) warned that “the rapid and continuous acquisition of mutations in mammals may predispose this virus to zoonotic infections”, meaning it could pass to humans.
The agency also raised concerns about limited wild bird and mammal surveillance and genomic data collection in England, and warned that there was insufficient testing of people who had come into contact with infected birds.
According to the World Health Organization (WHO), there have been approximately 870 cases of infection in humans in the past 20 years, and 457 of these infections have been fatal.