Biggest Ever Bird Flu Outbreak

Not all emerging infections are brand new kids on the biological block: some are old diseases in a new form. Flu is a good example. This is originally an infection of aquatic birds that has jumped into humans more recently, giving us human flu, but continues to circulate in its bird hosts as “bird flu” from where it occasionally makes new jumps into humans, spawning flu pandemics. And the more bird flu cases there are, the greater the risk of this happening. In fact, in recent months, many countries have seen massive bird flu activity. And much of that is down to us. Ian Brown monitors this at the Animal and Plant Health Agency...

Ian - Currently we're hopefully about to exit the largest ever outbreak the UK has had. And this is a problem that's not just in the UK, it's across Europe, across Central Asia, down in Africa, and into North America. So what's happening here is this bird flu strain has been evolving in wild birds. And of course, some of those wild birds move substantial distances on their normal migration, taking the virus with them and where they take that virus it will occasionally then spill over into poultry, chickens, turkeys, ducks, and this virus has a very highly lethality and it's happening now because this virus has improved its fitness. So a bit like COVID has done with new variants emerging, it's exactly the same. It's happened with birth flu. New variants have suddenly emerged over a period of time. And now we've got a particularly fit strain.

Chris - Given that flu has been around for thousands to millions of years. Why are we seeing this intensifying? Something must have changed which is driving this harder.

Ian - Yeah. That reflects a number of different systems. In some areas we rear and produce birds in a different way to how we used to. There's greater connectivity, there's greater density. So that means when a disease enters those birds, it's more easily able to spread. We also produce birds in an environment where connectivity with wild birds is relatively free and easy. So the virus can move between poultry and wild birds in both directions. Then you've got the dimension of climatic factors: urbanisation, wild birds will go through their annual cycle, which involves, for some species, migrating. And of course that is a key mechanism for moving this virus.

Chris - The parallels, as you highlight, with COVID are quite striking aren't they? So what you're seeing at the moment is a variant of the virus that's a bit like Omicron. It's evolved to become really easy to spread, but then you've got the human factor that also hands the trump card to the virus, because we've got loads and loads of animals all packed together in quite high density intensive farming. And then we've got the vector, which is like us on aeroplanes with COVID going on. Those wild birds from one henhouse to the next.

Ian - Behaviour is obviously a critical part. As you say, once the virus is in poultry of course, if we don't take steps to limit it's spread from one farm to another or one premise to another, then of course the virus is very able and efficient at doing that. And in some areas they do have this problem of stopping lateral spread as we say, spread between different sites and different farms.

Chris - What's the risk to humans? Is there one?

Ian - This virus in some circumstances can rarely jump to humans. We had a single case in the UK this winter which was through very close contact with birds, very mild clinical disease, and was only picked up through active surveillance. In some situations, people can get exposure to a very high dose and they can suffer more severe disease. That is a very rare event. And this virus is a bird virus. It wants to be in a bird. It does not want to be in a human.

Chris - But as we saw with Covid, one theory is that, this being a bat virus, it took people getting up close to bats and putting pressure on the virus, as it were, to jump the species barrier. It got into a person, once it's into a person, it can humanise. Is there not a risk that it could turn from something which is not very good at infecting humans into something that's much better at infecting humans. And then we could get an outbreak in humans of a new kind of flu?

Ian - Yeah. And that is a risk. And of course, that is the theory for the emergence of pandemic flu. Generally, when the virus is able to cross, it's because there's no hygiene measures being taken by those individuals. They're exposed to the birds and their secretions that are full of virus. So they get exposed to high amounts of virus. The second thing of course is managing the infection when they are in birds: taking prompt action to isolate those birds and deal with the outbreak effectively. And of course, that's what we aim to do internationally. So it's about prevention of exposure. It's about monitoring those people, but it's about taking action to control the infection effectively in birth. Now, if that is done, you can mitigate that risk. But where that isn't done, the virus has the opportunity to jump into a human and then maybe successfully make that transmission from one human to another.

Chris - Climate change is predicted to really shrink the amount of livable land area that we have available to us. It probably goes for animals too, doesn't it? So are we expecting to see more of this kind of thing in future, as more people and more animals converge on less and less resources; water, land, where they can live and therefore the opportunities for jumps like with bird flu, but other things as well.

Ian - Unfortunately, yes. It is a numbers game, isn't it? The more possibility for connectivity between these different populations, the more possibility pathogens can jump. Prior to 1997, the particular strain of bird flu we have now, causing these international episodes, was a very rare pathogen. Now, over the last 25 years, there have been changes in how we rear birds. There have been changes in how we rear poultry and how they connect with wild birds. All of those changes, influenced by different drivers, including climate change, where they bring that connectivity closer together, they increase the risk of a virus going from one population that it normally is present in into another new population that it doesn't normally reside in. And that has contributed undoubtedly to the increased scale of the problem with birth flu and all of that is good for a virus to spread. It's a perfect breeding ground.