User:Graham Beards/viruses/Introduction

__NOINDEX__ Viruses, for all intents and purposes, are invisible – we cannot see them, smell them or feel them. But viruses are everywhere; in the oceans, on the land, in the air, in plants and in our bodies, and those of all other animals. There are more viruses on Earth than all forms of life put together. We are only aware of their presence when they cause disease, but very few of the, probably, millions of different types of viruses actually do this. They have been around longer than humans – and pretty much everything else – and infected the first cells to have evolved on Earth. So bad is their reputation that it often comes as a surprise to discover that they are essential to life and have been a powerful force in evolution.

They were not discovered until relatively recently, and they have only been studied directly for the past 100 years. Before then, the diseases they caused were often thought to be caused by supernatural activity including the influence of the stars, and this is where the word "influenza" is derived from. Similar superstitions are still believed in some communities, which often make the control of the spread of viral infections difficult.

The 20th century was a golden age, and now much is known about viruses – what they are, what they do and where they came from. Despite their smallness, viruses are complex, and the way they reproduce in their host cells is even more so. This leads to difficulties in description because technical terms are often unavoidable. We have only one word for "cell" and, even more unfortunately, "messenger RNA". To have used definitions rather than such words, would have made the prose cumbersome. In the Wikipedia versions of the book's chapters, these terms are linked to other pages that explain them. This is difficult to achieve in print but will hopefully be addressed in later editions in the form of a glossary, when the corresponding Wikipedia article has been created. In the meantime, the reader might find my Wikipedia article Introduction to viruses useful.