Viruses cannot even perform the functions of living organisms until they invade other cells. Yet viruses cause some of the deadliest diseases that affect human beings: AIDS, SARS, Hanta and Ebola syndromes, herpes, the flu, and polio. Illustrated with microphotographs of the viruses, this book offers clear, straightforward explanations of how viruses cause these diseases, and it gives a realistic assessment of the danger they bring to human beings.