Virus History: Louis Pasteur and Germ Theory

Study Notes

Louis Pasteur, a French scientist, was a proponent of the germ theory of disease, which states that illnesses are caused by living microorganisms (microbes) that can spread between people and multiply in the body.
Pasteur identified and studied bacteria involved in diseases and disproved the idea of "spontaneous generation" of microbes.
He was unable to find the germ responsible for rabies, although he believed it existed, and later discovered that it was caused by viruses.
Other viral diseases known during Pasteur's time include the common cold, mumps, measles, and polio.
Pasteur developed the first vaccine for rabies in 1885, using a weakened extract of tissue infected with rabies, which was successfully tested on a 9-year-old boy named Joseph Meister.

In 1892, Russian scientist Dmitri Ivanovsky discovered that tobacco mosaic disease was caused by a filterable agent, which could not be trapped by a fine filter, leading him to believe it was not a bacterium.
Ivanovsky's findings were later confirmed by Dutch botanist Martinus Beijerinck, who concluded that the infectious agent was not a microbe but a "contagious living fluid".
Beijerinck coined the term "virus" from the Latin word for poison or pestilence.
In the 1930s, filters with tiny pores were developed, proving that viruses are particulate in nature, and the first electron microscopes were used to visualize viruses.

Viruses are not living cells like bacteria but rather tiny packets of genetic material.
They are responsible for various diseases, including rabies, common cold, mumps, measles, polio, foot-and-mouth disease, yellow fever, AIDS, and Ebola virus.
The discovery of viruses has led to a greater understanding of infectious diseases, but new viral diseases continue to emerge, challenging our knowledge of them.