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The 'germ theory of disease', also called the 'pathogenic theory of medicine', is a theory that proposes that microorganisms are the cause of many diseases. Although highly controversial when first proposed, it is now a cornerstone of modern medicine and clinical microbiology, leading to such important innovations as antibiotics and hygienic practices. Brock Biology of Microorganisms, Madigan M, Martinko J (editors)., , , Prentice Hall, 2005,
Thus saving many important lives.

Contents

History

Reception

Criticism

See also

References

External links

History

The ancient historical view was that disease was spontaneously generated instead of being created by microorganisms which grow by reproduction. The Atharvaveda is the first ancient text dealing with medicine. It identifies the causes of disease as living causative agents such as the yatudhānya, the kimīdi, the kṛimi and the durṇama. The atharvāns seek to kill them with a variety of drugs in order to counter the disease (see XIX.34.9). One of the earliest western references to this latter theory appears in ''On Agriculture'' by Marcus Terentius Varro (published in 36 BC) wherein there is a warning about locating a homestead in the proximity of swamps:
Girolamo Fracastoro proposed in 1546 that epidemic diseases are caused by transferable seedlike entities that could transmit infection by direct or indirect contact or even without contact over long distances.
Microorganisms were first directly observed by Anton van Leeuwenhoek, who is considered the father of microbiology.
The Italian Agostino Bassi is often credited with having stated the germ theory of disease for the first time, based on his observations on the lethal and epidemic muscardine disease of silkworms. In 1835 he specifically blamed the deaths of the insects on a contagious, living agent, that was visible to the naked eye as powdery spore masses; this microscopic fungus was subsequently called ''Beauveria bassiana'' in his honor.
Italian physician Francesco Redi provided proof against spontaneous generation. He devised an experiment where he used three flasks. He placed a meat loaf in each of the three flasks. He had one of the flasks 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 flask was covered by maggots, and the flask covered with gauze had maggots on the surface of the gauze. However, the tightly sealed flask had no maggots inside or outside it. He also noticed that the maggots were only found on surfaces that were accessible by flies. From this he concluded that spontaneous generation is not a plausible theory.
John Snow contributed to the formation of the germ theory when he traced the source of the 1854 cholera outbreak in the Soho neighbourhood of 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 contagion model, he identified drinking water as the vessel for transmission of the disease. He found that cases occurred in the homes which obtained their water from the Broad Street pump, which, not coincidentally, was at the center of the outbreak.
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.
Robert Koch was the first scientist to devise a series of proofs used to verify the germ theory of disease. Koch's Postulates were first used in 1875 to demonstrate anthrax was caused by the bacterium ''Bacillus anthrasis''. These postulates are still used today to help determine if a newly discovered disease is caused by a microorganism.

Reception

"Science proceeds by the death of scientists", and although Pasteur's demonstration essentially solved the question, the germ theory was not universally immediately accepted. The germ theory of disease was a theoretical foundation of epidemiology, the development and use of anti-microbial and antibiotic drugs, further vaccines after the empirically derived one for smallpox, hygienic practices in hospitals, and public sanitation. The germ theory provided a rationale for some existing practices and enabled others to be established.

Criticism

Though no one seriously disputes the germ theory outright, there are some who believe that it is incomplete as a theory of disease. The most commonly cited reason is the clinical inaccuracy of Koch's third postulate, which states that any susceptible animal infected with a pathogenic microbe should express symptoms. Koch himself later recanted this postulate after evidence showed asymptomatic carriers of typhoid and cholera.
Others' theories of disease accentuate the host resistance factors, arguing that germs are too ubiquitous to be viewed as the "cause" of disease, even if they are a necessary component of disease. These approaches typically accept the mechanics of the germ theory, but emphasize that heredity, public health, socioeconomic status, nutritional and/or immunologic status, or lifestyle are more important than germs themselves.
Many people with same or similar exposure to same microbes, may not all get similar infection and outcome under normal envoronment. It can be immune defence strength dependant. But immune strength, sucestibilities and senstivities related to particular microbe can also be dependant on instabilities and imbalanced in biochemistry of an indivdual. As such, it can be thought that any deviation from homeostasis can also be a reason to invite nd get any infection somewhat justify "miasma" or substance based theory.
Outside of science, previous theories ascribing disease to supernatural or divine agents also continue to have proponents.

See also

★ Rudolf Virchow

References

External links

★ Germ Theory of Disease—Supplemental Lecture (98/03/28 update) by Stephen T. Abedon

★ The Germ Theory Calendar by William C. Campbell

★ Science's war on infectious diseases