ANCIENT ENEMY
Many bacteria and viruses have been affecting man since antiquity, but there are many more that are of recent origin. We learn about the afflictions of our ancestors by studying human remains, art, and literature. The nature of the infection and its mode of transmission also help us determine how long a microbial organism has existed. Our knowledge of the plague, for example, is obtained through the writings and drawings of physicians, poets and writers who lived during a time when this "Pestilence" swept through the Old World, leaving death and despair. In retrospect, scientists were able to trace its deadly path through Europe and determine that the disease was caused by bacteria and transmitted by fleas -- both facts that were unknown to the medieval physician.
Based on the evidence available, it is clear that many infections are as old as humankind itself. Others have appeared only when changes in lifestyle and environment have allowed them to survive, or when they were able to infect animal hosts. While some organisms have been infecting humans in Europe, North Africa or Asia for a very long time, people living in the Americas, Australia, New Zealand, or the Pacific Islands were apparently free of those infections until European contact.
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Many disease-causing microbes have chosen humans as their only host. This represents both opportunity and liability. Their goal is to survive, but the strategies vary, which is a measure of how long man's relationship with them has existed.
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Unaware of the microbial cause of the disease, some blamed earthquakes or claimed that unseasonable winds had poisoned the air. People wore masks to avoid evil vapors, and carried herbs and perfumes to negate them. In the Middle Ages, people never suspected that bacteria transmitted by fleas carried by rats were spreading the disease. Medieval doctors had no miracle drugs and their treatments, which included bloodletting, enemas and a bland diet, proved powerless against these microbes.
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