Viruses cause everything from the common cold to cancer to multiple sclerosis to acquired immune deficiencey syndrome, or AIDS. This book is about viruses: what they do, how they live and the diseases they cause.

Viruses are tiny and incredibly simple biological "pirates" that invade living cells and then exploit the complex metabolic machinery of the cells to mass produce more viruses. In the most elemental sense, viruses do little more than enter cells, multiply, and then escape from the cells to enter new ones and start the whole business of multiplication all over again.

Almost all of the chemical reactions required to bring about this endless cycle are performed by the cells they invade, rather than by the viruses themselves. Despite the simplicity of viruses and the viral life cycle overall, however, the process of viral infection can follow an astonishing variety of paths, and rather than always being committed to rampant multiplication, viruses can often quitely take up residence within infected cells for long periods of time.

During the course of their wanderings from cell to cell the viruses can do a great deal of damage. The diseases they cause range from trivial infections such as the common cold to such deadly illnesses as smallpox, rabies, yellow fever and cancer. In between these two extremes come many other conditions such as influenza, chickenpox, measles, mumps, hepatitis, polio and many more -- all capable of killing, maining, or at least causing considerable discomfort for days, weeks, or even months. The viruses don't just attack humans, but can also infect other animals and plants.

While most of the book is written in a style that allows the reader with no medical background to easily digest the facts and problems about viruses, there are several chapters that can be understood only by those with background in complex biology and life sciences.

The book also raises the frightening specter of of using viruses as weapons. Such biological techniques have the potential to allow a war to be waged unnoticed. A biological attack could be disguised to appear as though it were a natural epidemic, or if carried out with cunning, could allow one nation to seriously and continuously damage another nation's economy without being detected.