Germ theory of disease
From Wikipedia, the free encyclopedia
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.
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[edit] Historical view of disease
The ancient historical view was that disease was spontaneously generated instead of being created by microorganisms which grow by reproduction. One of the earliest references to this theory appears in On Agriculture by Marcus Terentius Varro (published in 36 BCE) wherein there is a warning about locating a homestead in the proximity of swamps which reads "...and because there are bred certain minute creatures which cannot be seen by the eyes, which float in the air and enter the body through the mouth and nose and there cause serious diseases." (Varro On Agriculture 1,xii Loeb)
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 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.
Louis Pasteur demonstrated that fermentation and the growth of microorganisms in nutrient broths did not proceed by spontaneous generation. He exposed freshly boiled broths 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.
Italian physician Francesco Redi provided further 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 abiogenesis is not a plausible theory.
John Snow applied the germ theory to an outbreak of cholera, in opposition to the prevailing miasma theory of cholera. He plotted the source of the contagion to the Broad Street well water pump. Had his model of the world been one of contagion, the idea that the water was the source of the illness would not have been supported. Since adjacent families caught cholera or not, depending on where they got their water, the miasma theory could not easily have been applied.
[edit] Reception of the Germ Theory of Disease
"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. No mainstream medical professional today does not subscribe to the germ theory.
Previous theories ascribing disease to supernatural or divine agents continue to have proponents. Others accentuate the host resistance factors in disease, 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, or lifestyle are more important than germs themselves.
