Overview

By the late nineteenth century, the work of Louis Pasteur (1822-1895) and other scientists had established the germ theory of disease and identified the bacteria that caused many ailments.

But they found that some diseases were caused by invisible agents that could not be filtered out, agents that came to be called viruses. The experiments by Martinus Beijerinck (1851-1931) and Dmitri Ivanovsky on the tobacco mosaic virus in the 1890s are generally thought of as the beginning of the science of virology, but it was not until 40 years later that viruses could be isolated with extra-fine filters and imaged using electron microscopes.

Background

Infectious diseases have always been humanity's lot. Throughout history, plagues were not uncommon, and many people died of diseases that would be preventable or easily curable today. Early explanations of disease included possession by evil spirits and imbalance...