February 2, 2023

expert reaction to avian flu found in foxes and otters in the UK

There have been reports that the avian influenza outbreak in the UK has spilled over into mammals.

Prof Mark Fielder, Professor of Medical Microbiology, Kingston University, said:

“The ongoing H5N1 Avian influenza outbreak has been affecting flocks globally. More recently there has been some evidence of mammals that are testing positive for the virus. Whilst this is a situation that merits attention and surveillance, it is not yet a situation that should cause concern.

“The H5N1 influenza strain currently remains an avian virus, that appears to “want” to remain in birds. There is currently no genetic evidence that has changed to become more likely that the virus has adapted to a mammalian host. Whilst there have been situations where various different mammals from around the globe have picked up the virus there does not, at present seem to be any evidence that the virus has spread from mammal to mammal.

“It would appear more likely, in the current scenario, that the virus has been picked up when dead birds have been scavenged opportunistically. So it would appear likely that the virus was picked up during a meal but not passed on from fox to fox or between otters, as an example. There is no genetic evidence that the virus has changed to persist and spread in mammals at present. There would have to be a mutation that facilitates a change in how the virus infects cells for the virus to infect and maintain its presence in mammalian cells. So we are currently a far way from the virus having the capability jump and maintain its presence in mammalian population.

“There is currently no indication that the succession of necessary genetic changes to facilitate a longer-term species jump are present. That being said, there does need to be ongoing surveillance to monitor the virus, how it is changing and where it is changing, and population being infected.

“One of the things it is important to do globally is protect vulnerable species as much as possible, this is impossible with free flying wild birds, but we can control poultry and domesticated birds and limit their exposure to the virus by improving and maintaining biosecurity. If this is carried out both here and elsewhere, we can try to limit the spread of the virus as much as possible and reduce the chances of further spill over event.”

Prof Paul Wigley, Professor of Animal Microbial Ecosystems, School of Veterinary Science, University of Bristol, said:

“The main concern is these events indicate the wide distribution of H5N1 in birds in the UK. It also shows there is potential to cause disease in non-avian species. We have also seen recent reports of avian flu in mink farms in Spain.

“There is always a low risk of direct transmission to mammals. To cause a large scale spill over there would need to be transmission within or between mammalian species. To do this would likely need some genetic reassortment or mixing of influenza serotypes such as happened in the 2009 H1N1 or ‘swine flu’ pandemic.’ As pigs have been a potential vessel for this to occur in previous influenza outbreaks, entry into pig production is a particular concern.

“Whilst there is no transmission within mammalian populations, the risk to humans remains low. It does, however, illustrate that this remains a potential risk we need to be vigilant to.

“The ongoing avian influenza outbreak illustrates the need for more research funding and international cooperation to counter this threat.  Control in poultry to avoid spill overs to wildlife or other livestock is essential and there is a clear need to accelerate research to produce effective vaccines and enabling legislation in the longer term.  It is important we follow the good advice given by APHA/DEFRA to minimise risks.”

Dr Alastair Ward, Associate Professor of Biodiversity and Ecosystem Management, University of Leeds, said:

How worrying is this development?

“Symptoms in mammals can vary considerably, but mass mortality of affected mammals has not been experienced before. It’s finding in wild mammals in the UK is of concern, but there is currently no reason to expect that it will spread through wild mammal populations.

Has this been seen anywhere else in the world?

“Highly pathogenic avian influenza has spilled over from birds to mammals during previous outbreaks in other parts of the world, but it seems to be a rare event.

What needs to happen for this spillover into mammals?

“The species affected (foxes and otters) are known to scavenge. In all likelihood, the affected individuals will have scavenged infected wild bird carcasses, which may have had very high viral loads. Such high exposure is likely to have overwhelmed the mammal’s immune system, resulting in infection. There is currently no reason to suspect that the jump is due to a change in the virus’s genetic make-up.

Does this increase the risk of spillover events to humans?

“Probably not, although we cannot be 100% certain. Humans rarely come into contact with wild foxes or otters, and potentially infectious contact is likely to be rarer still. In the past, a relatively small number of humans who have lived or worked very closely with affected poultry e.g. in slaughter houses, have become infected with highly pathogenic avian influenza, with variable outcomes. Sensible biosecurity practices, such as avoiding contact with wild mammals and birds, wearing protective gloves and a face covering if contact is unavoidable, and washing of hands and soiled clothing with soap and water after exposure to affected environments should help maintain risks to humans at a minimum.”

Any other comments?

“Guidance on how to respond if you suspect an outbreak of avian influenza is available on government websites for each administration: https://www.gov.uk/government/news/bird-flu-avian-influenza-latest-situation-in-england#guidance, https://www.gov.scot/publications/avian-influenza-outbreaks/ , https://www.gov.wales/avian-influenza-bird-flu-latest-update , https://www.daera-ni.gov.uk/ai.”

Prof Ian Jones, Virologist at the University of Reading, said:

“Given its current prevalence in the bird population and the fact that influenza is known to infect mustelids it is not too surprising that avian flu has been found in animals that will have fed on infected carcasses. While these constant incursions of the virus into mammalian species does provide an opportunity for the virus to adapt to mammalian transmission, the natural barriers to this occurring are quite high and there is no indication of spread within these species. The risk to people right now therefore appears no more than it is for direct spread from infected birds.”

Bird flu (avian influenza): latest situation in England – GOV.UK (www.gov.uk)

Latest data published in December Bird flu (avian influenza): findings in non-avian wildlife – GOV.UK (www.gov.uk)

Declared interests

Prof Mark Fielder: “No conflicts to declare.”

Dr Alastair Ward: “I’m a member of the FluMAP project, funded by Defra and BBSRC to investigate the ongoing AIV outbreak in the UK.”

Prof Ian Jones: “No conflicts.”

For all other experts, no reply to our request for DOIs was received.