In 1796 British doctor Edward Jenner developed the first vaccine against a disease of viral origin: smallpox. However, it would take another century to discover what a virus is.
Neither Jenner nor other famous 19th century immunologists, such as Louis Pasteur, knew what pathogens their vaccines fought against.
Until that time, the best known infectious agents were bacteria , the smallest organisms discovered until then.
Pasteur , who in 1885 developed the vaccine Against rabies, he was never able to identify what caused the disease, but believed that it was a pathogen smaller than bacteria and therefore could not be detected by a microscope.
It was Pasteur’s assistant, Charles Chamberland, who provided the key piece that would lead to the discovery of the first virus.
Chamberland invented a filter, which bears his name, that allows bacteria to be removed.
The porcelain filter has pores smaller than bacteria, which allows them to be separated.
The French bacteriologist created this apparatus with the intention of producing bacteria-free water to use in his experiments with Pasteur.
But a Russian scientist gave it another use , opening the doors to the discovery of viruses.
Tobacco disease
Dmitri Ivanovsky was a Russian microbiologist and botanist.
A few years after Chamberland created his filter, began to investigate a disease that affected the tobacco plant, spreading rapidly and producing serious economic losses.
The evil had been identified a few years earlier in the Netherlands, where It was nicknamed tobacco mosaic , since it produced stains on the leaves that gave it that appearance.
The German scientist who identified the disease, Adolf Mayer, proved that it was infectious and, although he could not isolate the pathogen, he was convinced that it was a bacterium.
But Ivanovsky managed to prove that it was not a known infectious agent.
In 1885 ground leaves extracted from an infected plant and passed the culture through the Chamberland filter .
His experiment showed that the plant was still infected. In this way, he was able to verify that the infectious agent was not a bacterium , at least not a traditional one.
” Viruses ”
Although Ivanovsky could not identify what caused the tobacco mosaic disease – his main theory was that it could be a toxin produced by a bacterium – he did provide a key data.
It was able to determine that it was a filterable agent , giving rise to a new category of pathogens.
It was his Dutch counterpart, the botanist and microbiologist Martinus Willem Beijerinck , who made further progress with the study of this new infectious agent.
In addition to describing some of its properties, Beijerinck is credited with having baptized this pathogen as a “virus”, a word derived from a Latin term that means “viscous liquid” or “poison” , although some versions point out that it was Ivanovsky who first used the term.
In 1898, in his laboratory at Delft, Beijerinck replicated Ivanovsky’s work, again demonstrating that the plant of Tobacco infected with mosaic disease was still contagious after being filtered.
The scientist also showed that the infection could be transferred to other plants in a serial way, revealing that the pathogen in question was self-replicating and, therefore, was not a chemical toxin, as Ivanovsky speculated.
In addition, it verified that the causative agent could diffuse through several millimeters of gel.
It concluded that it was a liquid pathogen, which he called a contagium vivum fluidum (soluble living germ), ruling out that it was a contagium fixum (fixed or solid germ), such as bacteria.
Beijerinck described the virus as a living liquid that contained a dissolved entity, not particular and not corpuscular.
Despite the fact that Ivanovsky and Beijerinck’s investigations contained erroneous conclusions – years later the liquid nature of viruses would be ruled out and also that they were alive – they gave rise to a new branch of science: virology .
Plants, animals and humans
Tobacco mosaic virus (also known as TMV for its acronym in English) was the first virus identified in history, and continued to play a key role in the development of virology.
After the identification of this first virus in a plant, others began to be discovered in animals and humans.
In 1898, the same year that Beijerinck published his findings, two German colleagues, Friedrich Loeffler and Paul Frosch, used the Chamberland filter to investigate the pathogen that caused FMD in cattle.
Thus, they were able to determine that the disease was caused by a filtering agent le, as viruses were called at that time.
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The first human virus found was that of yellow fever, in Cuba, in 1901.
After Cuban doctor Carlos Finlay discovered that the vector of the disease was the mosquito, a special commission created by the United States Army (which occupied Cuba until 1902), managed to determine that the origin of the evil was a “filterable agent”.
It was the invention of the electron microscope , in 1931, which finally allowed scientists to see viruses and begin to understand their complex structures.
In 1935, the American biochemist and virologist Wendell Meredith S Tanley was the first to crystallize a virus -TMV-, showing that they remain active and infectious after crystallization.
Stanley’s experiment also revealed that viruses were not liquids but solid particles.
And found that they are made mostly of proteins .
His findings led him to receive the Nobel Prize in Chemistry in 1946, which he shared with two other scientists who worked with crystallization.
In the decade of 1950 it was discovered that in addition to proteins, viruses are composed of nucleic acids (DNA or RNA), which act as hereditary material.
From yellow fever to covid
In the last 120 years have been discovered more of 200 viruses that affect humans.
It is estimated that between three and four new species are discovered each year.
Some, such as smallpox, influenza and HIV / AIDS, have killed millions of people.
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How do pandemics end?
It remains to be determined how many people will lose their lives due to SARS -CoV-2, the type of coronavirus that is causing the covid pandemic – 19, and that has already caused almost 2 million deaths worldwide.
However, virologists have found that only a small handful of viruses harm us, of which intillion (a 1 followed by 30 zeros) that exist on Earth.
Most viruses are harmless . Some are beneficial, and there are even others that are indispensable for some species.
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