![]() The miasma theory was the predominant theory of disease transmission before the germ theory took hold towards the end of the 19th century it is no longer accepted as a correct explanation for disease by the scientific community. Eventually, a "golden era" of bacteriology ensued, during which the germ theory quickly led to the identification of the actual organisms that cause many diseases. Viruses were initially discovered in the 1890s. By the end of that decade, the miasma theory was struggling to compete with the germ theory of disease. ![]() ![]() This work was later extended by Robert Koch in the 1880s. A transitional period began in the late 1850s with the work of Louis Pasteur. However, such views were held in disdain in Europe, where Galen's miasma theory remained dominant among scientists and doctors.īy the early 19th century, smallpox vaccination was commonplace in Europe, though doctors were unaware of how it worked or how to extend the principle to other diseases. Infectious diseases are caused by biological agents such as pathogenic microorganisms (viruses, bacteria, and fungi) as well as parasites.īasic forms of germ theory were proposed by Girolamo Fracastoro in 1546, and expanded upon by Marcus von Plenciz in 1762. Pathogens are disease-carrying agents that can pass from one individual to another, both in humans and animals. Even when a pathogen is the principal cause of a disease, environmental and hereditary factors often influence the severity of the disease, and whether a potential host individual becomes infected when exposed to the pathogen. Diseases caused by pathogens are called infectious diseases. "Germ" refers to not just a bacterium but to any type of microorganism, such as protists or fungi, or even non-living pathogens that can cause disease, such as viruses, prions, or viroids. ![]() Their growth and reproduction within their hosts can cause disease. These small organisms, too small to be seen without magnification, invade humans, other animals, and other living hosts. It states that microorganisms known as pathogens or "germs" can affect disease. The germ theory of disease is the currently accepted scientific theory for many diseases. This is the bacterium that causes cholera. Scanning electron microscope image of Vibrio cholerae. ![]()
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