First human death from bird flu in the US

The United States has recorded their first human death from bird flu. The patient - who had underlying health conditions - was taken to a hospital in Louisiana after contracting the H5N1 virus but deteriorated. The infection is now spreading in cows and even killing domestic cats. So what’s the risk for us? To find out more, we put in a call to Ed Hutchinson from the MRC-University of Glasgow Centre for Virus Research…

Ed - We've been concerned about H5N1 bird flu for about 25 years now. It's a virus which is capable of causing severe disease in humans as well as spreading in birds. But it's become a real issue in recent years where a new strain of H5N1 has started spreading really aggressively around the world through birds, starting in Asia and then through into Europe, Africa, North America, South America, Antarctica. It's everywhere now. It's caused enormous problems with wild birds, but it's also been very good at jumping from those birds into other species, particularly into mammals. The most surprising case so far has been in the United States, where it's not only infected dairy cows, but it's become a dairy cow virus. It's fully adapted to spreading among cattle. There's now this big outbreak of H5N1 in cattle in the US.

Chris - And when it gets into a cow, does it behave like it does in the bird or does it behave more like mammalian flu, the kind of flu that you and I get: a runny nose, sore eyes, and a high temperature.

Ed - This was a real surprise to virologists. The first surprise was that cows got infected at all because up to this point we would have said that cattle, for whatever reason, didn't tend to get influenza A infections. But the second surprise was the way it spread. The main thing it's doing in these dairy cows is it's infecting the udders and it's being shed in the milk at incredibly high levels. Now, if you pasteurise milk, that kills the virus. That's good news. But if you don't, the milk remains infectious. That seems to be a good part of how it's spreading among these cattle now.

Chris - And what are the implications for people, then? Are we worried that the cows might act as an interface, enabling the infection to jump more efficiently to us?

Ed - Yes. Against the backdrop of the fact that the virus is still circulating in birds, within cattle (these are animals which are obviously found in large numbers) you have two points of contact. You have people who are working with the cattle, dairy workers. If you can imagine a big dairy, there are lots of opportunities to come into contact with milk from these cattle. The other is consumption of unpasteurised dairy products. There's a subculture of drinking what's called raw milk, unpasteurised milk. We pasteurise milk for good reasons, for killing all sorts of pathogens. This adds another one to the mix. So we are concerned that both humans and domesticated animals like pets could be exposed to the virus that way.

Chris - And have there been many human cases via those roots?

Ed - It's unclear at the moment whether there have been human cases from the consumption of raw milk, but there have definitely been cases from occupational exposure in dairies. These have generally been conjunctivitis, people getting pink eye probably from the milk coming into their eyes. Also some respiratory infections. And there have been cases where farm cats have died, almost certainly because they've been lapping up milk around the dairy. What we've also seen in the US and Canada have been two really severe cases of human infection, both of which put people in hospital, one of which sadly recently resulted in the patient dying. But these cases did not come from cattle. These came directly from viruses and birds. We can tell that because the viruses they got are much more closely related to the viruses still in birds than to the viruses which are in cows. This highlights the fact that we've now got two different places to look when we're thinking about risks of H5N1 infection of humans.

Chris - Does this not nevertheless put us on alert that this particular virus, this particular form of H5, appears to be quite good at getting into a range of mammals, of which group of animals we're obviously a member, and this might be the first steps towards a full incursion of this becoming a human flu?

Ed - It absolutely does. There are plenty of reasons to be worried about the animals themselves from an ecological perspective and animal welfare perspective, but if we're just going to look at humans for now, adapting to new species is a really difficult thing for a virus to do but flu is unusually good at it. It's good for two reasons. One is that it can mutate really quickly and we could see signs of that in those two really severe human cases. But the other thing to be concerned about is that influenza viruses can breed with each other. They can swap genes back and forth between them. If two different viruses infect one at the same time - we're currently in the middle of a winter flu season in the US and there are loads of people being infected with influenza viruses which are already very good at infecting humans - there is this risk that you could have an H5N1 virus swapping genes with a virus which is already good at growing in humans and getting a head start to becoming a human virus that way.

Chris - So you end up with a kind of hybrid virus that looks like H5N1, something we don't recognise as a human population, we've never seen that before, but it's got the inner workings of a human flu that knows really well how to grow in our cells and to grow really efficiently and spread really well.

Ed - That's absolutely right. And most of the influenza pandemics we've seen over the last century have occurred that way. Most recently, the 2009 swine flu outbreak occurred by different influenza viruses breeding with each other.

Chris - What then should public health officials, doctors, et cetera, be doing to A) keep an eye on that and B) minimise the risk?

Ed - The most important thing you can do is to keep an eye on it, because at the moment there is not any evidence for human to human transmission. We're not talking about a human outbreak right now. What we're talking about is the need to minimise the risk of the virus and figuring out how to do that. That involves minimizing the chances of the virus learning its way around humans. What does that involve? It involves biosecurity measures. If you have farmed animals, trying to reduce the risk of them getting infected. If you are working with animals which could be infected, both monitoring and wearing appropriate PPE, and this is legitimately quite a challenging thing to do in big complex farms, but it's important that this is considered. I'm also very concerned as lots people are consuming raw milk in areas where H5N1 is spreading.

Chris - What about vaccines? They're our mainstay for preventing seasonal flu. Have we got vaccines that will combat this form of H5 and have we got them at the sort of scale it would take if this suddenly does start to take off?

Ed - This is a partial good news story. We obviously know how to make influenza vaccines and we also already have produced H5N1 vaccines. Indeed, the UK government has recently purchased an initial batch of vaccines for exactly that reason. What's also good news is that you don't have to have a precisely matched H5 vaccine to get some protection against a virus. Even if it doesn't give you complete protection, it might reduce the risk of severe symptoms or reduce the risk of you spreading it to other people. This is very similar to what happens with seasonal influence vaccines and why it's always worth getting them, even if they're not going to completely protect you against every risk of infection.