Flu. Everyone is familiar with it. It comes along every so often and makes you utterly miserable during its stay, with headaches, fever, fatigue and the risk of death. Fortunately that last part isn’t common to every experience with flu, but it certainly does happen, killing hundreds of thousands of people each year.

So why is flu so dangerous? It’s a master of disguise. The flu virus has proteins on the outside of it which it uses to gain access to cells to infect them, and other proteins to help it get out of the cells it infects when it’s time to move on. These proteins, which I sometimes imagine as little keys and weapons, are called hemagglutinin and neuraminidase – the “H” and “N” that you see in the news when they refer to “H1N1” (swine flu). There are different forms of H and N, and when this differences are large, they get referred to by a different number – for example H7N8 (bird flu). The N and the H (the weapons and keys) are what the immune system can recognise and attack.

The reason flu is such a master of disguise is the way it keeps its genetic information. Unlike most plants, bacteria and animals (including humans and badgers), instead of having its genes part of DNA, its genes are comprised of RNA. For the unfamiliar, RNA is very similar to DNA, but instead of being two strands wrapped around each other – the “double helix” – RNA is only a single strand.

When DNA is copied, as it is every time a cell replicates, the machinery that carries out the copying has an error checking function, a bit like an auto-correcting spellchecker on a computer. Like a spellchecker, it occasionally misses a mistake or corrects with the wrong letter or word, but this is very rare. This means that mutations don’t happen very often when DNA is copied. However, when RNA is copied, this “spellchecker” doesn’t work nearly as well, or at all, and that means mutation happens much more often! That means that the N and H (keys and weapons) might be different enough for the immune system not to recognise them. This is called antigenic drift.

As well as the mistakes in copying leading to mutation, flu carries not one strand of RNA, but 8 smaller strands. These have the potential to become a little mixed up in an infected cell while the virus is replicating, and even more so if two different strains of the flu infect the same cell! This can result in big changes and a completely new strain, carrying bits and pieces of the two parent strains mixed in new ways. This is called antigenic shift, and the big threat here is that a strain that is really good at killing people – like bird flu – mixes with a strain that is good at moving from person to person, resulting in a new strain that can infect many people and hurt or kill a lot of them.

This has happened in the past several times and will happen again. In 1918, a strain of flu killed 3-5% of the population of the entire world. However, Doctors and other Scientists are well aware of the threat and are constantly on the lookout – which is why there was such a lot of attention payed to the strain of flu (Swine flu) in 2009/10 as it initially looked like it might be really dangerous. As I’ve said before, awareness can make a huge difference. A vaccine could probably be made for a new flu quite quickly, and there are drugs that can reduce the severity of flu if caught early enough (that target and damage the H and N keys and weapons) which many governments have stockpiled.

Biology Badger would therefore give the Flu a Doomwatch rating of “Scary” – it’s very likely to happen, and could be very bad, but there are many people preparing and watching for it. I’ll leave you now with this chilling panel from The Stand by Stephen King (marvel comics adaptation), a story with a particularly deadly flu strain…

Images: Crudely Drawn Virus Cartoons by Biology Badger. Comic panel from IGN.com, from Marvel Comics run of “Captain Tripps”, part of the comic adaption of The Stand by Stephen King. Title picture an electron micrograph of 1918 swine flu, from Wikipedia commons.