Before the 6 th century BC, the understanding of infections was based solely on religion and metaphysics. Demons, earthquakes, comets, and gods were perceived as the originators of the ailments that often befell humanity. Treatment was practiced through exorcism, and the gods were appeased to obtain their favor and protection (Karamanou, Panayiotakopoulos, Tsoucalas, Kousoulis & Androutsos, 2012).
The 6 th century BC, Alcameon, Pythagoras, and Empedocles ushered in a new era of diseases understanding. These minds and their school linked infections with the environment (Karamanou et al., 2012). This era is significant in advancing disease understanding as it establishes the commencement of understanding the true nature of infections. The concept developed into the miasma theory whereby diseases were believed to result from particles ( miasmas) that contaminated the air: the miasma was believed to emanate from putrefying matter (Karamanou et al., 2012). Infections such as cholera, tuberculosis, plague and skin diseases were ascribed to this phenomenon
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The Justinian plague led to the new development in the understanding of a newer theory, the theory of contagion that would soon revolutionize disease understanding. Evagrius Scholasticus (537-594AD) explains the spread of the Justinian plague proposing that it was due to contact with infected persons (Karamanou et al., 2012).
A breakthrough in the theory of contagion arrives in history after the works of scientist Girolamo Fracastoro (1478-1533AD). His theory attributed diseases to the work of seed-like beings, germs or seminaria via three routes: contact such as syphilis, clothing, and air such as tuberculosis (Karamanou et al., 2012). He understood germs to be chemical substances that would enter a host and cause chemical putrefaction. This is a primitive understanding of the germs however necessary for the concept of disease to advance to the next level. It is recognized as the first theory on contagious infection of diseases.
The next century witnessed great changes in understanding disease theory. With the development of the microscope by Anton van Leeuwenhoek, (1632-1723) new possibilities were opened however delayed. Nonetheless, the work of Francesco Redi (1626-1697) in this period is significant as he disproves the theory of spontaneous generation (Karamanou et al., 2012). The theory postulated that living things originated from non-living things due to the presence of the vital force, pneuma , in those things: Redi experimented and successfully disapproved the theory. Louis Pasteur (1822-1895) laid the final evidence to disprove the spontaneous generation theory by working on ferments (Karamanou et al., 2012). The conclusion of his study, on boiled meat broth, generated the germ theory and expanded the understanding that the germs were everywhere in the air.
The theory of germs cells was empowered by the works of Robert Koch (1843-1910) who discovers that specific bacteria are responsible for causing specific infections (Karamanou et al., 2012). Koch identifies specific bacteria and names them such as anthrax bacillus, tuberculosis bacillus, and Vibro cholerae. The year 1884 marked an important year in the understanding of disease and bacteria; Koch and Friedrich Loeffler (1852-1915) formulate the principles for determining the relationship between infection and the causative agent (Karamanou et al., 2012). According to the postulate
The microorganism must exist in abundance in the organisms suffering from its infection
The microorganism should not be found in healthy animals
It must be isolated and grown in pure culture
The cultured organism should cause the disease when introduced into a healthy animal
The microorganism must be isolated from the diseased and identified to be identical to the one introduced earlier on.
Overall, the development of the disease concept and causative agents has evolved greatly from the supernatural causes, miasma, contagion, spontaneous generation, and the germ theory. This development has changed the understanding and ability to cure diseases thereby improving life quality and expectancy.
References
Karamanou, M., Panayiotakopoulos, G., Tsoucalas, G., Kousoulis, A. A., & Androutsos, G. (2012). From miasmas to germs: a historical approach to theories of infectious disease transmission. Infez Med, 20 (1), 58-62.
