Bird flu

MicrobiologyBytes: Latest Updates

Influenza viruses are small.   Very small.   It would take a billion of them to cover the head of a pin. They're so small, you can't see them using an ordinary microscope. You have to use an electron microscope. Then, if you can find them, they look like this: All those bits on the surface of the virus particles are proteins. There are two kinds of protein on this virus. They're called haemagglutinin and neuraminidase. To make it easier to remember, we'll call them the H and N proteins.

My friend Russell has drawn this nice picture of an influenza virus particle. The twisted green bit in the middle is the virus' genes. This virus has naughty genes (we'll come back to those later). We can ignore all the other bits. (OK if you really want to know, click here) Those two proteins are important. The H protein lets the virus grab hold of cells and infect them. The N protein lets the virus get out of the cells it has infected. The virus needs those proteins. Without them, it can't reproduce. But those two proteins are also the virus' weak point and the way we can attack it.

How do we get the flu?

You catch flu from the respiratory secretions of another infected person. Yes, that's right folks, we're talking snot here! If someone coughs or sneezes near you, you may breathe in some of those secretions containing flu virus particles. More often however, you pick up the virus from an infected object that the other person has touched, then infect yourself by putting your fingers in your mouth or up your nose (yes you do, I've seen you).

But we're clever people - we're not scared of flu

We have a bunch of drugs which can help with flu infections:

• Symmetrel
• Relenza
• Tamiflu

but we don't have any drugs which guarantee to stop you getting flu in the first place. For that, we need a vaccine.

I have some good news and some bad news about flu vaccines. We know how to make vaccines against flu - we do it every year. You just grow up a whole mess of virus, knock the H and N proteins off the surface of the particles and inject them into someone's arm.

Except that - it doesn't always work.

 

Don't stop changing

Your genes are made of DNA (unless they're Calvin Klein :-), but influenza viruses' genes are made of RNA. That's one reason the virus keeps changing all the time. Although each flu virus only has one H and one N protein, we know there are at least 15 different H and N proteins, and there could be more. We can't make a vaccine which contains all the different the H and N proteins because it wouldn't work. Your immune system would just get confused.

But wait, it gets worse. As well as changing dramatically to form a completely new H or N protein, the flu virus also changes slowly all the time. Not a lot, but enough to make sure that a vaccine made against one strain of the virus may not work against a different strain in a few months time. And it takes up to a year to make and distribute a flu vaccine.

But this is bird flu

At the moment. But it's unlikely to stay that way. As well as humans, the really nasty types of influenza, the ones that make us ill, can also infect birds as well as other mammals such as horses, ferrets and pigs. And that's where the trouble starts. Flu virus likes to infect birds, particularly water birds such as ducks, geese and seabirds. And they don't stay in one place. They go on holiday. They may call it migration, but we both know it's just a holiday. And they take their flu viruses with them. And if it can't find a waterbird, the virus will infect a chicken. And humans eat chickens. And pigs.

At the moment, the scariest bird flu that's spreading around the world is called H5N1 (because of the H and N proteins it has). There are lots of other bird flu viruses (avian influenza if you like), but we don't hear much about those. We hear about H5N1. Because it kills people. But not very well.

Yet.

You're a pessimist

Or just a student of history. This isn't the first time this has happened. Ever hear about what happened in 1918? Don't take my word for it:

History of Influenza:

The 1918 "Spanish flu" pandemic killed between 20-40 million people. H5N1 isn't as deadly as the 1918 strain, but it might go that way. Or it might not. We just don't know yet.

America's Forgotten Pandemic: The Influenza of 1918
by Alfred W. Crosby.

Imagine that the world is gripped in the throes of the lengthy stalemate of a senseless war that has depleted Europe of most of its young men and resources, and those that remain are destitute, dispirited, starving, and suffering from the lost of loved ones. In the midst of this war, a formerly rather innocuous disease suddenly mutates into a new killer strain which infects all corners of the globe, from Alaska to Africa, within a matter of weeks. This new disease is not only remarkably contagious, but it is so lethal and destroys so many lives in such a short time-frame that even the ghastly global war pales in comparison. The scariest aspect of this tale is that it is not fiction.
(Amazon.co.UK)

So what's the worst that could happen?

• A pandemic of human-adapted avian influenza.
• Such a virus could have a mortality rate of 30-40%.
• Within a few months 10-25% of the world's population could be infected.
• 6.3 billion * 0.4 * 0.25 = over half a billion deaths.
• or worse ...

On the other hand

We have drugs available which were not available in 1918. In particular, antibiotics which can stop people dying of pneumonia. Which is great, if you live in a rich country with a good healthcare system. Not so great if you don't.

So should we worry about bird flu?

© MicrobiologyBytes 2007.