Historical Overview

“Poisons” were originally considered as the causative agents of illnesses that we know as viral diseases today. At that time, there were no standard methods to detect pathogenic (disease-causing) organisms such as bacteria and protozoa in the supposed “poisonous materials”. Only animal experiments performed by Louis Pasteur at the end of the nineteenth century, in which no dilution of the poisonous properties was achieved even after several passages, suggested that the disease-causing agent was able to multiply in the organism. Therefore, there was talk of a reproducible “virus” (Latin for “poison” or “slime”) in living organisms, and later also in cells. In St. Petersburg in 1892, Dimitri I. Ivanovski demonstrated that tobacco mosaic disease is caused by an “ultrafilterable” agent, whose size is significantly smaller than that of bacteria: tobacco mosaic virus (bacteria filters have a pore size of approximately 0.2 μm, however, most viruses are smaller than 0.1 μm). Soon afterwards, Martinus Willem Beijerinck came to the same conclusion: he developed, for the first time, the notion of a self-replicating, “liquid” agent (contagium vivum fluidum). The discovery of foot-and-mouth disease virus by Friedrich Loeffler and Paul Frosch in Greifswald in 1898 was the first evidence of an animal pathogenic virus.