THE MICROBIAL MENACE

I judged that even if 100 of these very wee animals lay stretched out one against another, they could not reach to the length of a grain of course sand...
— Antoni van Leeuwenhoek, describing bacteria, c.1676

Microbes, bacteria in particular, are the oldest and most abundant form of life — predating humans by about 3.5 billion years. Most microbes are benign or beneficial to humans, but the portion of the microbial world that is pathogenic (capable of producing disease) has periodically wreaked havoc on human populations. Epidemics (localized outbreaks of disease) and pandemics (global outbreaks) have occurred throughout human history.

Microscopic pathogens were once invisible and unknown to humans, but their effects have long been observable. The Old Testament dramatically describes plagues and infectious diseases, such as leprosy. Ancient Babylonian records refer to infectious diseases that we now know to be bacterial or viral in nature. Ancient Egyptian murals and writings graphically depict and describe infectious diseases that we can recognize and identify today.

The spread of infectious disease is episodic, changing, and seemingly unpredictable. Three of the most important factors or variables appear to be changes in the environment, the emergence of new species of pathogens, and the increased virulence of existing species through genetic mutation or change.