Originally, the word virus meant any poisonous substance, among which were included for a long time, for example, the venom of snakes. Viruses are truly fascinating biological structures that lie on the border between the inanimate and the living. Their sizes are between 100 and 1,000 times smaller than those of a cell.

The smallpox virus, one of the most lethal pathogens in history, is one of the largest, with a diameter of 200 nanometers. At the opposite pole are, for example, polioviruses – the cause of poliomyelitis with only 20 nm in diameter. These dimensions delayed its direct observation. It was not until the 1930s after the invention of the electron microscope, that we were able to see viruses for the first time despite the fact that we sensed their existence for a long time.

Treatments against unknown germs

In 1796 the British doctor Edward Jenner (1749-1823) developed the first vaccine in history, he did it against smallpox, and in 1885 the French scientist Louis Pasteur (1822-1895) did the same against rabies. In both cases they were viral diseases and the two scientists died without identifying the microorganism against which they had developed an effective treatment.

Charles Chamberland (1851-1908), a collaborator of Pasteur, provided the key piece that would end with the discovery of viruses. He developed a filter, which was baptized with his surname, made with pores smaller than the size of bacteria, so as to prevent the passage of them. With his filter, made of porcelain, he intended to obtain bacteria-free water, which could be used by Pasteur in his experiments.

In 1892, the microbiologist and botanist Dmitri Ivanovsky (1864-1920) studied a disease that affected the tobacco plant, an infection that spread extremely rapidly and caused millions in economic losses. The disease had been identified some time ago in the Netherlands and was known as tobacco mosaic, due to the characteristic spots that appeared on its leaves.

The first viruses are discovered
Ivanovsky ground the leaves of an infected plant, passed the obtained fluid through the Chamberland filter, and then brought the obtained fluid into contact with another plant. The scientist was amazed that the second plant acquired the infection, in other words, the infectious agent responsible for the tobacco mosaic disease was smaller than a bacterium.

Six years later, a Dutch microbiologist, Martinus W Beijererinck (1851-1931), reproduced Ivanovsky’s experiment in his laboratory in Delft, reaching the same conclusion. But the Dutchman also showed that the infection could be transferred to other plants, thus discovering that the pathogen was self-replicating.

Beijerinck christened the filterable agent” contagium vivum fluidum (living soluble germ), as opposed to bacteria, which were contagium fixum.”In this way, the existence of the first virus in history the one responsible for the tobacco mosaic disease was confirmed experimentally. The virology career had only just begun.

In 1898 two scientists, Friedrich Loeffler and Paul Frosch, demonstrated that the causative agent of foot-and-mouth disease in cattle was also a virus, and the discovery of the first human virus took just three years. In 1901 Walter Reed found the yellow fever virus. Despite the important advances made by Ivanovsky and Bijerinck, the liquid nature of viruses would later be ruled out and, most importantly, it would be called into question whether they were alive. But, as Rudyard Kipling would say, that is another story.