Science Matters: The elegant flu and its fine art of deception

I’m sick. Achy… sore throat… headache… fever…

Yep, like many people across the New England region, I’ve got the flu. 

It’s kind of amazing, when you think about it, just how much impact something that is only one 10 millionth of our size can have on us. Everyone knows how the flu makes us feel, but have you ever wondered what it actually is?

The influenza virus is such an elegant little thing. It’s tiny – really tiny – only about 120 nanometers across. If you lined up about 100 virions they would fit nicely across the diameter of just a single human cell. 

This is where the virus gets really sneaky...

These tiny little virions are roughly spherical in shape and, a bit like an onion (or an ogre), they have layers. 

Right in the middle is their genetic material. Unlike humans, the flu virus doesn’t have DNA. Instead, it has another type of genetic material called RNA. DNA and RNA are similar but not identical – same same but different. In your cells, your DNA contains all the instructions needed to make proteins. In the virus, these instructions are found in the RNA instead.

The viral RNA is protected by a layer of protein called a capsid. The capsid is kind of like a shell – it’s strong and rigid, and helps give the virus its shape.

Around the outside of the capsid is a third layer, called the envelope. The envelope is made of lipids – a group of molecules that include fats, oils and waxes. The cool thing about the envelope is that the virus doesn’t make it itself – it steals it from its host! Our cells are also surrounded by a membrane made of lipids. When the flu virus has finished replicating in our cells, it surrounds itself with some of this membrane, forming the envelope.

If you look at the flu virus under an electron microscope it looks kind of like a spiky ball. That’s because there are some special protein spikes embedded in the envelope layer. There are two types, called hemagglutinin and neuraminidase – usually just called the H and N proteins. These proteins help the virus to infect our cells – but they’re also the key to us being able to fight the virus.

The way our immune system fights off the flu virus is by producing antibodies that recognise those H and N proteins. The antibodies can then stick to the virus, and take it out of action. So it’s a bit of a stand off – the virus needs those proteins to infect cells, but our immune system, once it’s been exposed to those proteins once, is primed to defend against them.

This is where the virus gets really sneaky. It changes, just slightly, those H and N proteins. And when they change our immune system, our antibodies, can’t recognise them. Which is why we can catch the flu over and over again.

Right now, there’s not much I can do but wait. Eventually my immune system will win, and the virus will be gone… at least for a while.