A human case of bird flu has recently been detected in England. This news comes just days after restrictions were put in place to curb the virus's spread among wild birds and poultry in England and Scotland .
Author
- Ed Hutchinson
Professor, MRC-University of Glasgow Centre for Virus Research, University of Glasgow
Although cases of bird flu are surging among birds in the UK, the risk of the virus spreading to humans still remains extremely low. A bit of context about influenza explains why health protection agencies think this is the case.
There are many different influenza viruses out there. They're all related, but each specialises in infecting different types of animals.
Each winter, humans have to deal with three different types of seasonal influenza virus - H1N1, H3N2 and influenza B viruses . Meanwhile, birds, particularly shore birds and waterfowl, contend with a huge number of their own influenza viruses.
Most of these avian influenza viruses only afflict birds with minor infections of the airway or gut. But a small set cause more serious illness. These are called highly pathogenic avian influenza viruses ( HPAIVs ).
Among the HPAIVs, the H5N1 strains stand out. H5N1 bird flu, which is largely a disease of wild birds, has been notorious since the late 1990s for causing major die-offs of poultry worldwide - and for occasionally causing serious illness in humans. Viruses evolve rapidly, and in 2020 H5N1 evolved so it could spread more aggressively in wild birds.
The resulting outbreak tore through bird populations globally, including devastating die-offs in seabird colonies when the virus arrived in the UK in 2021. As it spread, the virus also caused outbreaks in farmed birds.
All outbreaks ebb and flow. After mid-2023, cases of H5N1 subsided in the UK. However, the virus never fully disappeared - and in autumn 2024, cases in wild birds started increasing again . It's very hard to keep wild birds and farmed birds apart, and infections in poultry farms soon followed.
In the UK, the threat of H5N1 to birds is tracked through ongoing surveillance. In response to these rising cases, avian influenza prevention zones have recently been declared for England, Scotland and now Wales . These restrictions aim to reduce the risk of farmed birds getting infected. Anyone keeping birds in England , Scotland and Wales will be required to take additional measures to prevent their birds being infected - including keeping birds under cover in regions facing the greatest risk.
These prevention zones are an important intervention. But given the current outbreak's scale in wild birds, these measures will at best only reduce the ongoing risk to farmed birds, rather than eliminating it.
What does this outbreak mean for humans?
Despite the serious problems H5N1 is causing for birds, the risk to humans is still very low. Because each virus is closely adapted to a particular host species , it's really hard for bird flu to infect a human.
When infections do occur, this is normally only in people who have close contact with birds - and even then it's an unusual event. The recent case of bird flu in a poultry worker in England is almost certainly an example of this sort of "spillover" infection.
It's good to hear the affected person is currently well and that antiviral drugs - which work against these viruses - have been offered to others who may have been exposed . The control measures announced over the weekend will help reduce the risk of other people who work with poultry getting infected.
If you don't have close contact with either wild or farmed birds, your chances of being infected are very low indeed. Still, if you come across any dead birds (particularly waterfowl), it's important to avoid handling them. Try to prevent pets from scavenging bird carcasses and avoid feeding pets raw bird meat from non-commercial sources . Sightings of dead or sick birds can be reported to health protection agencies .
Because influenza viruses are killed quickly by heat , there should be no risk to the public from eating properly-cooked eggs or poultry . The UK outbreak may also cause temporary difficulties in accessing free-range eggs and an increase in egg prices - things that have already been seen in the US , which is also experiencing a major H5N1 outbreak.
Is bird flu a problem anywhere else?
What's happening in the UK is just one part of an ongoing global H5N1 outbreak.
In some regions , strains of the virus have managed to spread beyond wild birds and infect mammals as well. In South America, H5N1 is causing devastating outbreaks in seals and sea lions. In the US, it has managed to adapt to dairy cattle and is being shed in their milk.
There have also been reported human infections. In the US, numerous farm workers have caught H5N1 from cattle , so far with relatively mild symptoms. There have also been two cases of severe illness in the US and Canada in people who caught a slightly different strain of H5N1 from birds, one of which sadly led to the patient's death .
These cases underscore the potential risks of H5N1 infections. But because human infections are so rare, how likely each strain of H5N1 is to cause severe disease in humans is still unclear. We also need to be on the lookout for any signs that any H5N1 strain anywhere might gain the ability to spread between humans. This would be an exceptionally unusual event - but to minimise the risk of future influenza pandemics, it's crucial situations like this are carefully monitored.
Nothing has been reported which suggests human-to-human transmission has occurred anywhere during the current outbreak. In the UK we have good surveillance for detecting any signs of this if it did. If wider spread did occur, the reserves of vaccines and antiviral drugs that we have in the UK would give us opportunities to intervene.
For now, bird flu remains a very real problem, but is primarily a problem for birds. By intervening now to protect farmed birds, we hope that we can keep it that way.
Ed Hutchinson receives funding from the Wellcome Trust and UKRI, including through the Flu:TrailMap-One Health consortium which is working to respond to the H5N1 outbreak. He has unpaid positions on the board of the European Scientific Working group on Influenza and other respiratory viruses (ESWI) and as a scientific adviser to PinPoint Medical.
