More than a piece of bad news wrapped in a protein

Too small to be seen with a conventional microscope, and capable of causing diseases that range from a mild cold to a rapid and painful death, it is not surprising that viruses cause mystification and fear. Where do they come from? Will new diseases like Aids emerge? When will the next influenza pandemic appear and how bad will it be? Why can we get rid of some viruses but carry others for life?

Some of medicine's greatest successes have been victories against viral diseases such as the eradication of smallpox and the nearly complete eradication of polio. But virus infections remain near the top of the list of medical and veterinary problems, as the epidemics of HIV and foot-and-mouth disease remind us.

Dorothy Crawford sets out to demystify viruses, and she does so in a lucid and comprehensive way. She gives clear and jargon-free answers to the sweeping questions posed above and to more mundane questions. But although she writes in a populist and accessible style, Crawford's book is a welcome counterweight to the sensationalism of "drama doc" books on emerging infections, in which the line between fact and fiction is blurred to the detriment of both. The details in Crawford's book are accurate, authoritative and up to date, but nevertheless digestible.

It will surprise many readers to learn of the positive aspects of viruses. The study of virology has led to huge advances in biology, for example in immunology, cancer and genetics. A whole branch of medical research has recently grown up around the subject of gene therapy, in which the hope is to introduce a healthy version of a mutated gene into cells to cure a rare and often untreatable genetic disease. A few years ago there was considerable debate over the best means to introduce the normal gene into the cell. It is now widely agreed that the most efficient means is to use a harmless virus as the carrier of the gene, because viruses have evolved to enter cells and can correct their function without damaging them.

There was perhaps scope for a separate chapter on the immune response of the viruses, which is an inseparable part of our understanding of how viruses do or do not cause disease. Trying to understand viral infections by looking only at the virus is rather like trying to understand a battle by studying the movements of the army on only one side.

The proof-reading has not been faultless, and some mistakes are irritating, such as the consistent misspelling of Stanley Prusiner's name throughout the book and in the index.

However, Crawford conveys well the interest and diversity of the subject, and she makes it clear that a virus is not merely, in Peter Medawar's phrase, "a little piece of bad news wrapped in a protein".

Charles R. M. Bangham is professor of immunology, Imperial College School of Medicine at St Mary's, London.