A viral platypus

Updated: Apr 15, 2019

Steve Wylie studies the smallest, strangest, most mind-bending organisms of all time - viruses.

Everyone knows that viruses cause the flu, common cold and a host of other diseases in plants and animals. But Steve and many virologists like him see them in a very different light. His journey to virus taxonomy followed a remarkably common path for virologists: he first just wanted to control them, but became increasingly fascinated by the viruses themselves, rather than the diseases they cause.

Like many good things in Australia, Steve's a kiwi. He grew up on the South Island of New Zealand and completed undergraduate training in plant physiology at Otago University. A PhD followed at Murdoch University, where he studied resistance of lupins to a serious agricultural virus, the bean yellow mosaic virus.

Viruses are one of the most abundant and ubiquitous life forms on Earth. Every drop of seawater contains around 10 million virus particles. Multiply that by the number of drops in the ocean, and the abundance of viruses starts to become apparent.

But that's just the beginning. As this blog notes, when you talk about viruses, you need to talk in very, very big numbers. Multiply the number of stars in the Universe by 10 million and you have an estimate for the number of viruses on Earth. Stack them all end-to-end, and you'd have a stack 200 million light years long, stretching way beyond the edge of our galaxy.

Our galaxy is over 100,000 light years across. A stack of all the viruses on Earth laid end to end would be nearly 2000 times wider than the galaxy. Image: publicdomainpictures.net

And bringing this right down to Earth, when you have a flu, your body probably harbours around 100 trillion flu viruses. No wonder you feel rotten.

As far as we know, there are no free-living viruses. Every one them needs a host - a bacterium, human or other organism - to function and reproduce. And every one of the more than ten million species of other organisms on Earth, from humans to fungi and bacteria, has specialised viruses living in and on them.

Viruses range in shape from simple rods or spheres to weird-looking things like a cross between a NASA moon lander and a hypodermic syringe. And these are only the more conventional ones. Many are simply naked strands of RNA or DNA. They have no "body" at all - they are infective molecules.

Many bacteriophages - viruses that infect bacteria - have an extraordinarily complex structure, which they use to dock with then infect bacterial cells. Image: BBC (https://www.bbc.com/news/health-21799534)

This great variety, and the very wide range of genetic mechanisms viruses use to reproduce, strongly suggests that they do not constitute a single branch of life on Earth. Rather, there have almost certainly been multiple origins for viruses. Some of them may represent the very first stages of the evolution of life, while others may represent the last - more conventional organisms that gradually stripp