Germ theory of disease
Encyclopedia
The germ theory of disease, also called the pathogenic theory of medicine, is a theory
that proposes that microorganism
s are the cause of many diseases. Although highly controversial when first proposed, germ theory was validated in the late 19th century and is now a fundamental part of modern medicine and clinical microbiology
, leading to such important innovations as antibiotics and hygienic practices
.
instead of being created by microorganisms which grow by reproduction. The Atharvaveda
, a sacred text of Hinduism
, is one of the earliest ancient texts dealing with medicine. It identifies the causes of disease as living causative agents such as the yatudhānya, the kimīdi, the kṛimi and the durṇama. The atharvāns seek to kill them with a variety of drugs in order to counter the disease (see XIX.34.9). One of the earliest Western references to this latter theory appears in On Agriculture by Marcus Terentius Varro
(published in 36 BC), wherein there is a warning about locating a homestead in the proximity of swamps:
Girolamo Fracastoro
proposed in 1546 that epidemic diseases are caused by transferable seed-like entities that could transmit infection by direct or indirect contact or even without contact over long distances. The Italian Agostino Bassi
is often credited with having stated the germ theory of disease for the first time, based on his observations on the lethal and epidemic muscardine
disease of silkworms. In 1835 he specifically blamed the deaths of the insects on a contagious, living agent, that was visible to the naked eye as powdery spore masses; this microscopic fungus was subsequently called Beauveria bassiana
in his honor.
Microorganisms were first directly observed by Anton van Leeuwenhoek
, who is considered the father of microbiology
. Building on Leeuwenhoek's work, physician Nicolas Andry
argued in 1700 that microorganisms he called "worms" were responsible for smallpox
and other diseases. Ignaz Semmelweis
was a Hungarian
obstetrician working at Vienna's Allgemeines Krankenhaus
in 1847, when he noticed the dramatically high incidence of death from puerperal fever
among women who delivered at the hospital with the help of the doctors and medical students. Births attended by the midwives were relatively safe. Investigating further, Semmelweis made the connection between puerperal fever and examinations of delivering women by doctors, and further realized that these physicians had usually come directly from autopsies. Asserting that puerperal fever was a contagious
disease and that matter from autopsies were implicated in its development, Semmelweis made doctors wash their hands with chlorinated lime water before examining pregnant women, thereby reducing mortality from childbirth from 18% to 2.2% at his hospital. Nevertheless, he and his theories were viciously attacked
by most of the Viennese medical establishment.
John Snow
contributed to the formation of the germ theory when he traced the source of the 1854 cholera
outbreak in Soho, London. The statistical analysis of the affected cases showed that the outbreak was not consistent with the miasma theory
which was prevalent at the time. Contrary to the miasma model, he identified drinking water as the vessel for transmission of the disease. He found that cases occurred in the homes which obtained their water from the Broad Street pump, which was at the geographical center of the outbreak.
Italian physician Francesco Redi
provided early evidence against spontaneous generation
. He devised an experiment in 1668 where he used three jars. He placed a meat loaf and egg in each of the three jars. He had one of the jars open, another one tightly sealed, and the last one covered with gauze. After a few days, he observed that the meat loaf in the open jar was covered by maggots, and the jar covered with gauze had maggots on the surface of the gauze. However, the tightly sealed jar had no maggots inside or outside it. He also noticed that the maggots were only found on surfaces that were accessible by flies. From this he concluded that spontaneous generation is not a plausible theory. Louis Pasteur
further 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 broth 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, therefore the living organisms that grew in such broths came from outside, as spores on dust, rather than being generated within the broth.
Robert Koch
was the first scientist to devise a series of tests used to assess the germ theory of disease. Koch's Postulates
were published in 1890, and derived from his work demonstrating that anthrax was caused by the bacterium
Bacillus anthracis
. These postulates are still used today to help determine if a newly discovered disease is caused by a microorganism.
In the 1870s Joseph Lister
was instrumental in developing practical applications of the germ theory of disease with respect to surgical techniques.
Scientific theory
A scientific theory comprises a collection of concepts, including abstractions of observable phenomena expressed as quantifiable properties, together with rules that express relationships between observations of such concepts...
that proposes that microorganism
Microorganism
A microorganism or microbe is a microscopic organism that comprises either a single cell , cell clusters, or no cell at all...
s are the cause of many diseases. Although highly controversial when first proposed, germ theory was validated in the late 19th century and is now a fundamental part of modern medicine and clinical microbiology
Microbiology
Microbiology is the study of microorganisms, which are defined as any microscopic organism that comprises either a single cell , cell clusters or no cell at all . This includes eukaryotes, such as fungi and protists, and prokaryotes...
, leading to such important innovations as antibiotics and hygienic practices
Hygiene
Hygiene refers to the set of practices perceived by a community to be associated with the preservation of health and healthy living. While in modern medical sciences there is a set of standards of hygiene recommended for different situations, what is considered hygienic or not can vary between...
.
History
The ancient historical view was that disease was spontaneously generatedSpontaneous generation
Spontaneous generation or Equivocal generation is an obsolete principle regarding the origin of life from inanimate matter, which held that this process was a commonplace and everyday occurrence, as distinguished from univocal generation, or reproduction from parent...
instead of being created by microorganisms which grow by reproduction. The Atharvaveda
Atharvaveda
The Atharvaveda is a sacred text of Hinduism and one of the four Vedas, often called the "fourth Veda"....
, a sacred text of Hinduism
Hinduism
Hinduism is the predominant and indigenous religious tradition of the Indian Subcontinent. Hinduism is known to its followers as , amongst many other expressions...
, is one of the earliest ancient texts dealing with medicine. It identifies the causes of disease as living causative agents such as the yatudhānya, the kimīdi, the kṛimi and the durṇama. The atharvāns seek to kill them with a variety of drugs in order to counter the disease (see XIX.34.9). One of the earliest Western references to this latter theory appears in On Agriculture by Marcus Terentius Varro
Marcus Terentius Varro
Marcus Terentius Varro was an ancient Roman scholar and writer. He is sometimes called Varro Reatinus to distinguish him from his younger contemporary Varro Atacinus.-Biography:...
(published in 36 BC), wherein there is a warning about locating a homestead in the proximity of swamps:
Girolamo Fracastoro
Girolamo Fracastoro
Girolamo Fracastoro was an Italian physician, poet, and scholar in mathematics, geography and astronomy. Fracastoro subscribed to the philosophy of atomism, and rejected appeals to hidden causes in scientific investigation....
proposed in 1546 that epidemic diseases are caused by transferable seed-like entities that could transmit infection by direct or indirect contact or even without contact over long distances. The Italian Agostino Bassi
Agostino Bassi
Agostino Bassi, sometimes called de Lodi, was an Italian entomologist. He preceded Louis Pasteur in the discovery that microorganisms can be the cause of disease...
is often credited with having stated the germ theory of disease for the first time, based on his observations on the lethal and epidemic muscardine
Beauveria bassiana
Beauveria bassiana is a fungus that grows naturally in soils throughout the world and acts as a parasite on various arthropod species, causing white muscardine disease; it thus belongs to the entomopathogenic fungi. It is being used as a biological insecticide to control a number of pests such as...
disease of silkworms. In 1835 he specifically blamed the deaths of the insects on a contagious, living agent, that was visible to the naked eye as powdery spore masses; this microscopic fungus was subsequently called Beauveria bassiana
Beauveria bassiana
Beauveria bassiana is a fungus that grows naturally in soils throughout the world and acts as a parasite on various arthropod species, causing white muscardine disease; it thus belongs to the entomopathogenic fungi. It is being used as a biological insecticide to control a number of pests such as...
in his honor.
Microorganisms were first directly observed by Anton van Leeuwenhoek
Anton van Leeuwenhoek
Antonie Philips van Leeuwenhoek was a Dutch tradesman and scientist from Delft, Netherlands. He is commonly known as "the Father of Microbiology", and considered to be the first microbiologist...
, who is considered the father of microbiology
Microbiology
Microbiology is the study of microorganisms, which are defined as any microscopic organism that comprises either a single cell , cell clusters or no cell at all . This includes eukaryotes, such as fungi and protists, and prokaryotes...
. Building on Leeuwenhoek's work, physician Nicolas Andry
Nicolas Andry
Nicolas Andry de Bois-Regard was a French physician and writer. He played a significant role in the early history of both parasitology and orthopedics, the name for which is taken from Andry's book Orthopédie.-Early life and career:...
argued in 1700 that microorganisms he called "worms" were responsible for smallpox
Smallpox
Smallpox was an infectious disease unique to humans, caused by either of two virus variants, Variola major and Variola minor. The disease is also known by the Latin names Variola or Variola vera, which is a derivative of the Latin varius, meaning "spotted", or varus, meaning "pimple"...
and other diseases. Ignaz Semmelweis
Ignaz Semmelweis
Ignaz Philipp Semmelweis was a Hungarian physician now known as an early pioneer of antiseptic procedures. Described as the "savior of mothers", Semmelweis discovered that the incidence of puerperal fever could be drastically cut by the use of hand disinfection in obstetrical clinics...
was a Hungarian
Hungary
Hungary , officially the Republic of Hungary , is a landlocked country in Central Europe. It is situated in the Carpathian Basin and is bordered by Slovakia to the north, Ukraine and Romania to the east, Serbia and Croatia to the south, Slovenia to the southwest and Austria to the west. The...
obstetrician working at Vienna's Allgemeines Krankenhaus
Vienna General Hospital
The Vienna General Hospital is the University medical center of the city of Vienna, Austria. The AKH is the largest hospital of Austria and Europe, the second largest hospital in the world, and at 85-m high is one of the tallest hospital buildings in the world...
in 1847, when he noticed the dramatically high incidence of death from puerperal fever
Puerperal fever
Puerperal fever or childbed fever, is a bacterial infection contracted by women during childbirth or miscarriage. It can develop into puerperal sepsis, which is a serious form of septicaemia. If untreated, it is often fatal....
among women who delivered at the hospital with the help of the doctors and medical students. Births attended by the midwives were relatively safe. Investigating further, Semmelweis made the connection between puerperal fever and examinations of delivering women by doctors, and further realized that these physicians had usually come directly from autopsies. Asserting that puerperal fever was a contagious
Contagious disease
A contagious disease is a subset category of infectious diseases , which are easily transmitted by physical contact with the person suffering the disease, or by their secretions or objects touched by them....
disease and that matter from autopsies were implicated in its development, Semmelweis made doctors wash their hands with chlorinated lime water before examining pregnant women, thereby reducing mortality from childbirth from 18% to 2.2% at his hospital. Nevertheless, he and his theories were viciously attacked
Contemporary reaction to Ignaz Semmelweis
Dr. Ignaz Semmelweis discovered in 1847 that hand-washing with a solution of chlorinated lime reduced the incidence of fatal childbed fever tenfold in maternity institutions...
by most of the Viennese medical establishment.
John Snow
John Snow (physician)
John Snow was an English physician and a leader in the adoption of anaesthesia and medical hygiene. He is considered to be one of the fathers of epidemiology, because of his work in tracing the source of a cholera outbreak in Soho, England, in 1854.-Early life and education:Snow was born 15 March...
contributed to the formation of the germ theory when he traced the source of the 1854 cholera
Cholera
Cholera is an infection of the small intestine that is caused by the bacterium Vibrio cholerae. The main symptoms are profuse watery diarrhea and vomiting. Transmission occurs primarily by drinking or eating water or food that has been contaminated by the diarrhea of an infected person or the feces...
outbreak in Soho, London. The statistical analysis of the affected cases showed that the outbreak was not consistent with the miasma theory
Miasma theory of disease
The miasma theory held that diseases such as cholera, chlamydia or the Black Death were caused by a miasma , a noxious form of "bad air"....
which was prevalent at the time. Contrary to the miasma model, he identified drinking water as the vessel for transmission of the disease. He found that cases occurred in the homes which obtained their water from the Broad Street pump, which was at the geographical center of the outbreak.
Italian physician Francesco Redi
Francesco Redi
Francesco Redi was an Italian physician, naturalist, and poet.-Biography:The son of Gregorio Redi and Cecilia de Ghinci was born in Arezzo on February 18, 1626. After schooling with the Jesuits, he attended the University of Pisa...
provided early evidence against spontaneous generation
Spontaneous generation
Spontaneous generation or Equivocal generation is an obsolete principle regarding the origin of life from inanimate matter, which held that this process was a commonplace and everyday occurrence, as distinguished from univocal generation, or reproduction from parent...
. He devised an experiment in 1668 where he used three jars. He placed a meat loaf and egg in each of the three jars. He had one of the jars open, another one tightly sealed, and the last one covered with gauze. After a few days, he observed that the meat loaf in the open jar was covered by maggots, and the jar covered with gauze had maggots on the surface of the gauze. However, the tightly sealed jar had no maggots inside or outside it. He also noticed that the maggots were only found on surfaces that were accessible by flies. From this he concluded that spontaneous generation is not a plausible theory. Louis Pasteur
Louis Pasteur
Louis Pasteur was a French chemist and microbiologist born in Dole. He is remembered for his remarkable breakthroughs in the causes and preventions of diseases. His discoveries reduced mortality from puerperal fever, and he created the first vaccine for rabies and anthrax. His experiments...
further demonstrated between 1860 and 1864 that fermentation
Fermentation (food)
Fermentation in food processing typically is the conversion of carbohydrates to alcohols and carbon dioxide or organic acids using yeasts, bacteria, or a combination thereof, under anaerobic conditions. Fermentation in simple terms is the chemical conversion of sugars into ethanol...
and the growth of microorganisms in nutrient broths did not proceed by spontaneous generation. He exposed freshly boiled broth 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, therefore the living organisms that grew in such broths came from outside, as spores on dust, rather than being generated within the broth.
Robert Koch
Robert Koch
Heinrich Hermann Robert Koch was a German physician. He became famous for isolating Bacillus anthracis , the Tuberculosis bacillus and the Vibrio cholerae and for his development of Koch's postulates....
was the first scientist to devise a series of tests used to assess the germ theory of disease. Koch's Postulates
Koch's postulates
Koch's postulates are four criteria designed to establish a causal relationship between a causative microbe and a disease. The postulates were formulated by Robert Koch and Friedrich Loeffler in 1884 and refined and published by Koch in 1890...
were published in 1890, and derived from his work demonstrating that anthrax was caused by the bacterium
Bacteria
Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...
Bacillus anthracis
Bacillus anthracis
Bacillus anthracis is the pathogen of the Anthrax acute disease. It is a Gram-positive, spore-forming, rod-shaped bacterium, with a width of 1-1.2µm and a length of 3-5µm. It can be grown in an ordinary nutrient medium under aerobic or anaerobic conditions.It is one of few bacteria known to...
. These postulates are still used today to help determine if a newly discovered disease is caused by a microorganism.
In the 1870s Joseph Lister
Joseph Lister, 1st Baron Lister
Joseph Lister, 1st Baron Lister OM, FRS, PC , known as Sir Joseph Lister, Bt., between 1883 and 1897, was a British surgeon and a pioneer of antiseptic surgery, who promoted the idea of sterile surgery while working at the Glasgow Royal Infirmary...
was instrumental in developing practical applications of the germ theory of disease with respect to surgical techniques.
See also
- Cell theoryCell theoryCell theory refers to the idea that cells are the basic unit of structure in every living thing. Development of this theory during the mid 17th century was made possible by advances in microscopy. This theory is one of the foundations of biology...
- Alexander FlemingAlexander FlemingSir Alexander Fleming was a Scottish biologist and pharmacologist. He wrote many articles on bacteriology, immunology, and chemotherapy...
- Robert HookeRobert HookeRobert Hooke FRS was an English natural philosopher, architect and polymath.His adult life comprised three distinct periods: as a scientific inquirer lacking money; achieving great wealth and standing through his reputation for hard work and scrupulous honesty following the great fire of 1666, but...
- Miasma theory
- Louis PasteurLouis PasteurLouis Pasteur was a French chemist and microbiologist born in Dole. He is remembered for his remarkable breakthroughs in the causes and preventions of diseases. His discoveries reduced mortality from puerperal fever, and he created the first vaccine for rabies and anthrax. His experiments...
- Rudolf VirchowRudolf VirchowRudolph Carl Virchow was a German doctor, anthropologist, pathologist, prehistorian, biologist and politician, known for his advancement of public health...
- Zymotic diseaseZymotic diseaseZymotic diseases , an obsolete term in medicine, formerly applied to the class of acute infectious maladies, presumed to be due to some virus or organism which acts in the system like a ferment...
External links
- Germ Theory of Disease—Supplemental Lecture (98/03/28 update) by Stephen T. Abedon
- The Germ Theory Calendar by William C. Campbell
- Science's war on infectious diseases