The Germ Theory of Disease
The germ theory of diseases describes that diseases are caused by tiny germs invading the human body. This is an accepted scientific theory for many diseases. These tiny germs invade human beings and animals. Their reproduction within the host causes diseases.
Finding the Relationship between Germs and Diseases
Girolamo Fracastoro (1478–1553) proposed that diseases are caused by invisible living organisms transmitted from one person to another. This was further supported by Marcus Von Plenciz. Plenciz not only stated that living germs are the causative agents of diseases but also said that different germs are responsible for different diseases. However, many people believed that diseases are caused by supernatural forces, poisonous vapors (Miasmas), and an imbalance of four humors (blood, phlegm, yellow bile, and black bile) present in the body. That means the Germ theory was still dominated by Galen’s Miasma theory until the early nineteenth century. Many scientists had proposed the germ theory, even much before Pasteur’s experiment. But all those proposals remained unrecognized.
Agostino Bassi (1773–1856) was the first one to identify the contributing factors for disease caused by microorganisms in 1835.
Later, the concept of “Germs to Diseases” became quite general during the 19th century.
In 1842, Oliver Wendell Holmes (1809–1894) believed that Puerperal fever, a disease of childbirth, was caused by a germ carried from one mother to another by midwives and physicians. At the same time, Ignaz Philipp Semmelweis. (1818–1865) from Hungary, started using antiseptics for hand disinfection during obstetrical operations. He also explained the importance of hand disinfection to other physicians and advised them to use it. This has gradually reduced the rate of deaths caused due to infections associated with childbirth. Semmelweis was called as “Saviour of Mothers”.
Semmelweis published the “Concept and Prophylaxis of Childbed Fever” in 1861. His work was ignored though, the concept of antisepsis was brought to life by the experiments of Joseph Lister in England. Later, the importance of antisepsis was completely understood and appreciated by the medical profession.
On the other side, Louis Pasteur (1822–1895) successfully worked on the fermentation issues and Pebrine disease. Pebrine is a silk-warm disease that ruined the silk industry in France. Pasteur was then challenged to work on Anthrax by the French government. Anthrax is a disease of cattle, sheep, and rarely human beings. He isolated the microbes from the blood of infected animals.
Koch’s Postulates
Simultaneously, Robert Koch (1843–1910) was also working on Anthrax in Germany. Because of his interest in bacteriology, he continued to work on Anthrax and discovered that the germs that cause anthrax, are rod-shaped. He also isolated these germs from the blood of animals that died of anthrax.
In his experiments, he inoculated the isolated germs into a healthy animal. Then he observed that these animals had developed similar kinds of symptoms of Anthrax. He finally provided the first evidence that bacteria are the causative agents of diseases in animals. This has led him to establish Koch’s postulates, a series of 4 principles, to support the Germ to disease concept.
- The organism must always be present, in every case of the disease.
- The organism must be isolated from a host containing the disease and grown in pure culture.
- Samples of the organism taken from pure culture must cause the same disease when inoculated into a healthy animal, in the laboratory.
- The organism must be isolated from the inoculated animal and must be identified as the same original organism that was first isolated from the originally diseased host.
Although Koch’s postulates provided guidelines to identify the cause of the disease, there were some limitations that could not be answered at those times.
The postulates explain some infectious diseases but not viruses, as techniques were not developed to isolate viruses during the 1800s. Therefore, it was believed that Koch’s postulates apply to only a few infectious diseases.
As per the third postulate, the experimental animal should develop the disease, but it did not happen in every case because of asymptomatic carriers, immunity, and genetic resistance.
Koch’s postulates fail to explain prion diseases (a type of protein that can trigger normal proteins in the brain, to fold abnormally), and other agents that cannot be grown in cultures.
The germ theory of disease has transformed the field of medicine, greatly influencing our understanding of the causes, prevention, and treatment of illnesses. From its controversial hypothesis to widespread acceptance, the germ theory of diseases has brought extraordinary advancements in public health, clinical medicine, and biomedical research. Its recognition of microorganisms as agents of disease paved the way for innovative discoveries in immunology, microbiology, and molecular biology, while its emphasis on sanitation and infection control measures has saved countless lives and mitigated the impact of epidemics and pandemics.
