-DUBEY, PRAVEEN KUMAR

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.

Causal structure of the germ theory of disease.

Several theories were advanced form time to time to explain disease causation such as the supernatural theory of disease, the theory of humors by Greeks and Indians, the theory of contagion, the miasmatic theory which attributed disease to noxious air and vapors, the theory of spontaneous generation (abiogenesis) etc. The breakthrough came in 1860, when the French bactieriologist Louis Pasteur (1822- 1895) demonstrated the presence of bacteria in air. He disapproved the theory of “spontaneous generation”.

Louis Pasteur 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 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 unless the flasks were broken open; therefore, the living organisms that grew in such broths came from outside, as spores on dust, rather than spontaneously 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 anthracis.

Koch’s postulates are as follows: The microorganism must be found in abundance in all

organisms suffering from the disease, but should not be found in healthy animals.

The microorganism must be isolated from a diseased organism and grown in pure culture.

The cultured microorganism should cause disease when introduced into a healthy organism.

The microorganism must be reisolated from the inoculated, diseased experimental host and identified as being identical to the original specific causative agent.

These postulates are still used today to help determine if a newly discovered disease is caused by a microorganism.

The discoveries of Pasteur and Koch confirmed the germ theory of disease. It was the golden age in bacteriology. Microbe after microbe was discovered in quick succession- gonococcus in 1847, typhoid bacillus, pneumococcal in 1880, tubercule bacillus in 1882, cholera vibrio in 1883, diphtheria bacillus in 1884.

The concept of cause embodied in the germ theory of disease is generally referred to as a one-to-one relationship between causal agent and disease. The disease model accordingly is:

Disease agent man disease

The germ theory of disease, though it was revolutionary concept, led many epidemiologists to take one sided view of disease causation. That is, they could not think beyond the germ theory of disease. It is now recognized that a disease is rarely caused by a single agent alone, but rather depends upon a number of factors which contribute to its occurrence. This demanded a broader concept of disease causation that synthesized the basic factors of agent, host and environment (epidemiological triad).

PARK’S TEXTBOOK OF PREVENTIVE AND SOCIAL MEDICINE – K.PARK

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