Germ Theory of Disease - History

History

Girolamo Fracastoro proposed in 1546 that epidemic diseases are caused by transferable seed-like entities that transmit infection by direct or indirect contact or even without contact over long distances. The Italian Agostino Bassi was the first person to prove that a disease was caused by a microorganism when he conducted a series of experiments between 1808 and 1813, demonstrating that a "vegetable parasite" caused a disease in silkworms known as calcinaccio. This disease was devastating the French silk industry at the time. The "vegetable parasite" is now known to be a fungus pathogenic to insects called Beuveria bassiana (named after Agnostino Bassi). However, germ theory is more commonly attributed to Louis Pasteur (1822-1895) and Robert Koch (1843-1910). Pasteur discovered that another serious disease of silkworms, pebrine, was caused by a small microscopic organism now known as Nosema bombycis (1870). Pasteur saved the silk industry in France by developing a method to screen silkworms eggs for those that are not infected, a method that is still used today to control this and other silkworm diseases. Koch is known for developing four basic criteria (known as Koch's Postulates) for demonstrating, in a scientifically sound manner, that a disease is caused by a particular organism. These postulates grew out of his seminal work with the anthrax using purified cultures of the pathogen that had been isolated from diseased animals.

Microorganisms were first directly observed by Anton van Leeuwenhoek, who is considered the father of microbiology. Building on Leeuwenhoek's work, physician Nicolas Andry argued in 1700 that microorganisms he called "worms" were responsible for smallpox and other diseases. Ignaz Semmelweis was a Hungarian obstetrician working at Vienna's Allgemeines Krankenhaus in 1847, when he noticed the dramatically high incidence of death from puerperal fever among women who delivered at the hospital with the help of the doctors and medical students. Births attended by the midwives were relatively safe. Investigating further, Semmelweis made the connection between puerperal fever and examinations of delivering women by doctors, and further realized that these physicians had usually come directly from autopsies. Asserting that puerperal fever was a contagious disease and that matter from autopsies were implicated in its development, Semmelweis made doctors wash their hands with chlorinated lime water before examining pregnant women, thereby reducing mortality from childbirth from 18% to 2.2% at his hospital. Nevertheless, he and his theories were viciously attacked by most of the Viennese medical establishment.

John Snow contributed to the formation of the germ theory when he traced the source of the 1854 cholera outbreak in Soho, London. The statistical analysis of the affected cases showed that the outbreak was not consistent with the miasma theory, which was prevalent at the time. Contrary to the miasma model, he identified drinking water as the vessel for transmission of the disease. He found that cases occurred in the homes that obtained their water from the Broad Street pump, which was at the geographical center of the outbreak.

Italian physician Francesco Redi provided early evidence against spontaneous generation. He devised an experiment in 1668 in which he used three jars. He placed a meatloaf and egg in each of the three jars. He had one of the jars open, another one tightly sealed, and the last one covered with gauze. After a few days, he observed that the meat loaf in the open jar was covered by maggots, and the jar covered with gauze had maggots on the surface of the gauze. However, the tightly sealed jar had no maggots inside or outside it. He also noticed that the maggots were found only on surfaces that were accessible by flies. From this he concluded that spontaneous generation is not a plausible theory. Louis Pasteur further demonstrated between 1860 and 1864 that fermentation and the growth of microorganisms in nutrient broths did not proceed by spontaneous generation. He exposed freshly boiled broth to air in vessels that contained a filter to stop all particles passing through to the growth medium: and even with no filter at all, with air being admitted via a long tortuous tube that would not pass dust particles. Nothing grew in the broths, therefore the living organisms that grew in such broths came from outside, as spores on dust, rather than being generated within the broth. Abraham Groves developed aseptic surgery techniques in the 1870s because he considered surgical infections to be transmitted by fluids as he knew typhoid was spread