Germ theory of disease in the context of Pathogenicity

Ritual purification is a ritual prescribed by a religion through which a person is considered to be freed of uncleanliness, especially prior to the worship of a deity, and ritual purity is a state of ritual cleanliness. Ritual purification may also apply to objects and places. Ritual uncleanliness is not identical with ordinary physical impurity, such as dirt stains; nevertheless, body fluids are generally considered ritually unclean.

Most of these rituals existed long before the germ theory of disease, and figure prominently from the earliest known religious systems of the Ancient Near East. Some writers connect the rituals to taboos.

The 19th century in science saw the birth of science as a profession; the term scientist was coined in 1833 by William Whewell, which soon replaced the older term of (natural) philosopher.

Among the most influential ideas of the 19th century were those of Charles Darwin (alongside the independent research of Alfred Russel Wallace), who in 1859 published the book On the Origin of Species, which introduced the idea of evolution by natural selection. Another important landmark in medicine and biology were the successful efforts to prove the germ theory of disease. Following this, Louis Pasteur made the first vaccine against rabies, and also made many discoveries in the field of chemistry, including the asymmetry of crystals. In chemistry, Dmitri Mendeleev, following the atomic theory of John Dalton, created the first periodic table of elements. In physics, the experiments, theories and discoveries of Michael Faraday, Andre-Marie Ampere, James Clerk Maxwell, and their contemporaries led to the creation of electromagnetism as a new branch of science. Thermodynamics led to an understanding of heat and the notion of energy was defined.

The history of biology traces the study of the living world from ancient to modern times. Although the concept of biology as a single coherent field arose in the 19th century, the biological sciences emerged from traditions of medicine and natural history reaching back to Ayurveda, ancient Egyptian medicine and the works of Aristotle, Theophrastus and Galen in the ancient Greco-Roman world. This ancient work was further developed in the Middle Ages by Muslim physicians and scholars such as Avicenna. During the European Renaissance and early modern period, biological thought was revolutionized in Europe by a renewed interest in empiricism and the discovery of many novel organisms. Prominent in this movement were Vesalius and Harvey, who used experimentation and careful observation in physiology, and naturalists such as Linnaeus and Buffon who began to classify the diversity of life and the fossil record, as well as the development and behavior of organisms. Antonie van Leeuwenhoek revealed by means of microscopy the previously unknown world of microorganisms, laying the groundwork for cell theory. The growing importance of natural theology, partly a response to the rise of mechanical philosophy, encouraged the growth of natural history (although it entrenched the argument from design).

Over the 18th and 19th centuries, biological sciences such as botany and zoology became increasingly professional scientific disciplines. Lavoisier and other physical scientists began to connect the animate and inanimate worlds through physics and chemistry. Explorer-naturalists such as Alexander von Humboldt investigated the interaction between organisms and their environment, and the ways this relationship depends on geography—laying the foundations for biogeography, ecology and ethology. Naturalists began to reject essentialism and consider the importance of extinction and the mutability of species. Cell theory provided a new perspective on the fundamental basis of life. These developments, as well as the results from embryology and paleontology, were synthesized in Charles Darwin's theory of evolution by natural selection. The end of the 19th century saw the fall of spontaneous generation and the rise of the germ theory of disease, though the mechanism of inheritance remained a mystery.

John Snow (15 March 1813 – 16 June 1858) was an English physician and a leader in the development of anaesthesia and medical hygiene. He is considered one of the founders of modern epidemiology and early germ theory, in part because of his work in tracing the source of a cholera outbreak in London's Soho, which he identified as a particular public water pump. Snow's findings inspired fundamental changes in the water and waste systems of London, which led to similar changes in other cities, and a significant improvement in general public health around the world.

In biology, a pathogen (Greek: πάθος, pathos "suffering", "passion" and -γενής, -genēs "producer of"), in the oldest and broadest sense, is any organism or agent that can produce disease. A pathogen may also be referred to as an infectious agent, or simply a germ.

The term pathogen came into use in the 1880s. Typically, the term pathogen is used to describe an infectious microorganism or agent, such as a virus, bacterium, protozoan, prion, viroid, or fungus. Small animals, such as helminths and insects, can also cause or transmit disease. However, these animals are usually referred to as parasites rather than pathogens. The scientific study of microscopic organisms, including microscopic pathogenic organisms, is called microbiology, while parasitology refers to the scientific study of parasites and the organisms that host them.

A severe outbreak of cholera occurred in 1854 near Broad Street (now Broadwick Street) and Golden Square in Soho, London, England, during the worldwide 1846–1860 cholera pandemic. The outbreak (also known as Golden Square outbreak), which killed 616 people, is best known for the physician John Snow's study of its causes and his hypothesis that germ-contaminated water was the cause, rather than something in the air called "miasma". This discovery influenced public health and the construction of improved sanitation facilities beginning in the mid-19th century. Later, the term "focus of infection" was used to describe sites, such as the Broad Street pump, where conditions are favourable for transmission of infection. Snow unknowingly took advantage of a natural experiment during his endeavours to identify the cause of cholera transmission.

The history of herbalism is closely tied with the history of medicine from prehistoric times up until the development of the germ theory of disease in the 19th century. Modern medicine from the 19th century to today has been based on evidence gathered using the scientific method. Evidence-based use of pharmaceutical drugs, often derived from medicinal plants, has largely replaced herbal treatments in modern health care. However, many people continue to employ various forms of traditional or alternative medicine. These systems often have a significant herbal component. The history of herbalism also overlaps with food history, as many of the herbs and spices historically used by humans to season food yield useful medicinal compounds, and use of spices with antimicrobial activity in cooking is part of an ancient response to the threat of food-borne pathogens.

Marko Anton Plenčič, Marcus von Plenciz or Marcus Antonius von Plenciz (28 April 1705 – 25 November 1786) was a Slovenian physician in Vienna who was among the early adopters of the germ or contagion theory of infection at a time when infectious disease was attributed to bad air or miasmas. He published his theories in Opera medico-physica 1762. He has been called the Slovene Pasteur.

Plenčič was born in Salcan near Görtz/Gorizia where he studied before going to study medicine in Vienna and Padua. Graduating in 1735, he practiced in Vienna until his death. His 1762 book Opera medico-physica had four parts and he described the theory of germs that he called animalcula minima or animalcula insensibilia as being the cause of infectious diseases with his focus being on rinderpest. Among his teachers was Carlo Francesco Cogrossi (1682–1769) who had also identified microbes as causal organisms for disease. Plenčič suggested that earthquakes such as the one in 1755 had helped the spread of rinderpest. He hypothesized that each disease was caused by a different organism dwelling within the human body, but was unable to offer proof. He suggested treatments that worked against the microbes as cures although the agents he suggested were antiseptics and heavy metal compounds. He was an honorary professor at the Vienna Medical School and was titled as a nobleman by Maria Theresa in 1764 and knighted in 1770.

The miasma theory (also called the miasmic theory) is an abandoned medical theory that held that diseases—such as cholera, chlamydia, or plague—were caused by a miasma (μίασμα, Ancient Greek for pollution), a noxious form of "bad air", also known as night air. The theory held that epidemics were caused by miasma, emanating from rotting organic matter. Though miasma theory is typically associated with the spread of contagious diseases, some academics in the early 19th century suggested that the theory extended to other conditions, as well, e.g. one could become obese by inhaling the odor of food.

The miasma theory was advanced by Hippocrates in the fifth century BC and accepted from ancient times in Europe and China. The theory was eventually abandoned by scientists and physicians after 1880, replaced by the germ theory of disease; specific germs, not miasma, caused specific diseases. However, cultural beliefs about getting rid of odor made the clean-up of waste a high priority for cities. It also encouraged the construction of well-ventilated hospital facilities, schools, and other buildings.

Bacillus anthracis is a gram-positive and rod-shaped bacterium that causes anthrax, a deadly disease to livestock and, occasionally, to humans. It is the only permanent (obligate) pathogen within the genus Bacillus. Its infection is a type of zoonosis, as it is transmitted from animals to humans. It was discovered by a German physician Robert Koch in 1876, and became the first bacterium to be experimentally shown as a pathogen. The discovery was also the first scientific evidence for the germ theory of diseases.

B. anthracis measures about 3 to 5 μm long and 1 to 1.2 μm wide. The reference genome consists of a 5,227,419 bp circular chromosome and two extrachromosomal DNA plasmids, pXO1 and pXO2, of 181,677 and 94,830 bp respectively, which are responsible for the pathogenicity. It forms a protective layer called endospore by which it can remain inactive for many years and suddenly becomes infective under suitable environmental conditions. Because of the resilience of the endospore, the bacterium is one of the most popular biological weapons. The protein capsule (poly-D-gamma-glutamic acid) is key to evasion of the immune response. It feeds on the heme of blood protein haemoglobin using two secretory siderophore proteins, IsdX1 and IsdX2.