A GENERAL INTRODUCTION
Individual viruses have evolved interesting and unique lifestyles. One consequence is that battles have been won or lost when a particular virus infected one army but not its adversaries. Viruses have depleted the native populations of several continents. Entire countries have been changed geographically, economically, and religiously as a result of sweeping virus infections that were impervious to known cures.
Smallpox alone, in the twentieth century, has killed an estimated 300 million individuals, about threefold as many persons as all the wars of this century ( 1).* In the sixteenth and seventeenth centuries, smallpox killed emperors of Japan and Burma, as well as kings and queens of Europe, thereby altering dynasties, control of countries, and alliances ( 2). Earlier, the successful conquest of Mexican Aztec and Peruvian Inca empires by a handful of Span-____________________