Chris Smith interviews Dr Paul Digard from the Division of Virology at the University of Cambridge
Part of the show Avian Flu, How Flu Spreads and How to Avoid It
Paul - 'Flu's a virus, so it grows by taking over cells in your body and turning them into factories that replicate more virus. The cells 'flu infects are found in your airway and upper respiratory tract. It infects you by you breathing it in, it gets into your lungs, replicates in them and then to get out and infect another person, you have to cough or sneeze the new viruses out, so they can be passed on.
Chris - So I breathe it in, it locks onto my cells, turns them into virus factories and I go down with it. But how does it actually get out of me, in terms of getting out of the cells that it's infected? How does it do that?
Paul - The virus factories are releasing new particles from their surface all the time. One infected cell will produce 10 000 new virus particles. The peculiar thing about flu is that it makes two sorts of virus particles. There's one sort that's very small, about one ten thousandth of a millimetre across, like a standard sized virus particle. But there's a second sort, which is a hair like structure, and we call it a filament. It's an interesting question as to why the viruses make these filaments, because the filaments are very large for a virus. These things are easily 20 to 50 times the length of a normal virus.
Chris - So what do you think they do?
Paul - it's a very good question, because if you think about the virus factory, it can produce about 10000 particles of the small size, but the amount of material needed to make one of these hair like structures is 20 to 50 times more. So that's 20 to 50 times less particles that can be made in that one infected cell.
Chris - So they must be pretty important to the cell and have quite an important job to do then.
Paul - Yes, exactly. The virus wouldn't do it without a compelling reason. And I have to say that we don't know what the reason is, but the best hypothesis we have at the moment is that it's involved in getting past the mucus layer. Your respiratory tract is lined with a mucus layer as a protective barrier against all sorts of nastiness in the outside world. This forms a coating over the cells, and it's possible that these filaments are a way of reaching past that barrier.
Chris - It's almost as though flu has it's own snot escape kit then.
Paul - Yes, the filaments can poke past this layer of snot and release virus much closer to the open air than when it's in the layer of gunk covering your nasal passage.