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The history of virology – the scientific study of
virus A virus is a submicroscopic infectious agent that replicates only inside the living cells of an organism. Viruses infect all life forms, from animals and plants to microorganisms, including bacteria and archaea. Since Dmitri Ivanovsk ...
es and the
infection An infection is the invasion of tissues by pathogens, their multiplication, and the reaction of host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmissible disease or communicable di ...
s they cause – began in the closing years of the 19th century. Although
Louis Pasteur Louis Pasteur (, ; 27 December 1822 – 28 September 1895) was a French chemist and microbiologist renowned for his discoveries of the principles of vaccination, microbial fermentation and pasteurization, the latter of which was named afte ...
and
Edward Jenner Edward Jenner, (17 May 1749 – 26 January 1823) was a British physician and scientist who pioneered the concept of vaccines, and created the smallpox vaccine, the world's first vaccine. The terms ''vaccine'' and ''vaccination'' are derived f ...
developed the first
vaccine A vaccine is a biological preparation that provides active acquired immunity to a particular infectious or malignant disease. The safety and effectiveness of vaccines has been widely studied and verified.
s to protect against viral infections, they did not know that viruses existed. The first evidence of the existence of viruses came from experiments with filters that had pores small enough to retain bacteria. In 1892, Dmitri Ivanovsky used one of these filters to show that sap from a diseased tobacco plant remained infectious to healthy tobacco plants despite having been filtered.
Martinus Beijerinck Martinus Willem Beijerinck (, 16 March 1851 – 1 January 1931) was a Dutch microbiologist and botanist who was one of the founders of virology and environmental microbiology. He is credited with the discovery of viruses, which he called "'' ...
called the filtered, infectious substance a "virus" and this discovery is considered to be the beginning of
virology Virology is the scientific study of biological viruses. It is a subfield of microbiology that focuses on their detection, structure, classification and evolution, their methods of infection and exploitation of host cells for reproduction, the ...
. The subsequent discovery and partial characterization of
bacteriophage A bacteriophage (), also known informally as a ''phage'' (), is a duplodnaviria virus that infects and replicates within bacteria and archaea. The term was derived from "bacteria" and the Greek φαγεῖν ('), meaning "to devour". Bac ...
s by
Frederick Twort Frederick William Twort FRS (22 October 1877 – 20 March 1950) was an English bacteriologist and was the original discoverer in 1915 of bacteriophages (viruses that infect bacteria). He studied medicine at St Thomas's Hospital, London, was super ...
and Félix d'Herelle further catalyzed the field, and by the early 20th century many viruses had been discovered. In 1926, Thomas Milton Rivers defined viruses as obligate parasites. Viruses were demonstrated to be particles, rather than a fluid, by
Wendell Meredith Stanley Wendell Meredith Stanley (16 August 1904 – 15 June 1971) was an American biochemist, virologist and Nobel laureate. Biography Stanley was born in Ridgeville, Indiana, and earned a BSc in Chemistry at Earlham College in Richmond, Indiana. ...
, and the invention of the
electron microscope An electron microscope is a microscope that uses a beam of accelerated electrons as a source of illumination. As the wavelength of an electron can be up to 100,000 times shorter than that of visible light photons, electron microscopes have a hi ...
in 1931 allowed their complex structures to be visualised.


Pioneers

Despite his other successes,
Louis Pasteur Louis Pasteur (, ; 27 December 1822 – 28 September 1895) was a French chemist and microbiologist renowned for his discoveries of the principles of vaccination, microbial fermentation and pasteurization, the latter of which was named afte ...
(1822–1895) was unable to find a causative agent for
rabies Rabies is a viral disease that causes encephalitis in humans and other mammals. Early symptoms can include fever and tingling at the site of exposure. These symptoms are followed by one or more of the following symptoms: nausea, vomiting, ...
and speculated about a pathogen too small to be detected using a microscope. In 1884, the French
microbiologist A microbiologist (from Greek ) is a scientist who studies microscopic life forms and processes. This includes study of the growth, interactions and characteristics of microscopic organisms such as bacteria, algae, fungi, and some types of para ...
Charles Chamberland (1851–1931) invented a filter – known today as the
Chamberland filter A Chamberland filter, also known as a Pasteur–Chamberland filter, is a porcelain water filter invented by Charles Chamberland in 1884. It was developed after Henry Doulton, Henry Doulton's ceramic water filter of 1827. It is similar to the ...
– that had pores smaller than bacteria. Thus, he could pass a solution containing bacteria through the filter and completely remove them from the solution. In 1876,
Adolf Mayer Adolf Eduard Mayer (9 August 184325 December 1942) was a German Agricultural chemistry, agricultural chemist whose work on Tobacco mosaic virus, tobacco mosaic disease played an important role in the discovery of tobacco mosaic virus and viruses ...
, who directed the Agricultural Experimental Station in
Wageningen Wageningen () is a municipality and a historic city in the central Netherlands, in the province of Gelderland. It is famous for Wageningen University, which specialises in life sciences. The municipality had a population of in , of which many ...
, was the first to show that what he called "Tobacco Mosaic Disease" was infectious. He thought that it was caused by either a toxin or a very small bacterium. Later, in 1892, the Russian biologist Dmitry Ivanovsky (1864–1920) used a Chamberland filter to study what is now known as the
tobacco mosaic virus ''Tobacco mosaic virus'' (TMV) is a positive-sense single-stranded RNA virus species in the genus ''Tobamovirus'' that infects a wide range of plants, especially tobacco and other members of the family Solanaceae. The infection causes characteri ...
. His experiments showed that crushed leaf extracts from infected tobacco plants remain infectious after filtration. Ivanovsky suggested the infection might be caused by a
toxin A toxin is a naturally occurring organic poison produced by metabolic activities of living cells or organisms. Toxins occur especially as a protein or conjugated protein. The term toxin was first used by organic chemist Ludwig Brieger (1849 ...
produced by bacteria, but did not pursue the idea. In 1898, the Dutch microbiologist
Martinus Beijerinck Martinus Willem Beijerinck (, 16 March 1851 – 1 January 1931) was a Dutch microbiologist and botanist who was one of the founders of virology and environmental microbiology. He is credited with the discovery of viruses, which he called "'' ...
(1851–1931), a microbiology teacher at the Agricultural School in
Wageningen Wageningen () is a municipality and a historic city in the central Netherlands, in the province of Gelderland. It is famous for Wageningen University, which specialises in life sciences. The municipality had a population of in , of which many ...
repeated experiments by
Adolf Mayer Adolf Eduard Mayer (9 August 184325 December 1942) was a German Agricultural chemistry, agricultural chemist whose work on Tobacco mosaic virus, tobacco mosaic disease played an important role in the discovery of tobacco mosaic virus and viruses ...
and became convinced that filtrate contained a new form of infectious agent. He observed that the agent multiplied only in cells that were dividing and he called it a ''
contagium vivum fluidum ''Contagium vivum fluidum'' (Latin: "contagious living fluid") was a phrase first used to describe a virus, and underlined its ability to slip through the finest-mesh filters then available, giving it almost liquid properties. Martinus Beijerinck ...
'' (soluble living germ) and re-introduced the word ''virus''. Beijerinck maintained that viruses were liquid in nature, a theory later discredited by the American biochemist and virologist
Wendell Meredith Stanley Wendell Meredith Stanley (16 August 1904 – 15 June 1971) was an American biochemist, virologist and Nobel laureate. Biography Stanley was born in Ridgeville, Indiana, and earned a BSc in Chemistry at Earlham College in Richmond, Indiana. ...
(1904–1971), who proved that they were in fact, particles. In the same year, 1898,
Friedrich Loeffler Friedrich August Johannes Loeffler (; 24 June 18529 April 1915) was a German bacteriologist at the University of Greifswald. Biography He obtained his M.D. degree from the University of Berlin in 1874. He worked with Robert Koch from 1879 to 1884 ...
(1852–1915) and Paul Frosch (1860–1928) passed the first animal virus through a similar filter and discovered the cause of
foot-and-mouth disease Foot-and-mouth disease (FMD) or hoof-and-mouth disease (HMD) is an infectious and sometimes fatal viral disease that affects cloven-hoofed animals, including domestic and wild bovids. The virus causes a high fever lasting two to six days, follo ...
. The first human virus to be identified was the yellow fever virus. In 1881,
Carlos Finlay Carlos Juan Finlay (December 3, 1833 – August 20, 1915) was a Cuban epidemiologist recognized as a pioneer in the research of yellow fever, determining that it was transmitted through mosquitoes ''Aedes aegypti''. Biography Early life and ...
(1833–1915), a Cuban physician, first conducted and published research that indicated that mosquitoes were carrying the cause of yellow fever, a theory proved in 1900 by commission headed by Walter Reed (1851–1902). During 1901 and 1902, William Crawford Gorgas (1854–1920) organised the destruction of the mosquitoes' breeding habitats in Cuba, which dramatically reduced the prevalence of the disease. Gorgas later organised the elimination of the mosquitoes from Panama, which allowed the
Panama Canal The Panama Canal ( es, Canal de Panamá, link=no) is an artificial waterway in Panama that connects the Atlantic Ocean with the Pacific Ocean and divides North and South America. The canal cuts across the Isthmus of Panama and is a condui ...
to be opened in 1914. The virus was finally isolated by
Max Theiler Max Theiler (30 January 1899 – 11 August 1972) was a South African-American virologist and physician. He was awarded the Nobel Prize in Physiology or Medicine in 1951 for developing a vaccine against yellow fever in 1937, becoming the first ...
(1899–1972) in 1932 who went on to develop a successful vaccine. By 1928 enough was known about viruses to enable the publication of ''Filterable Viruses'', a collection of essays covering all known viruses edited by Thomas Milton Rivers (1888–1962). Rivers, a survivor of
typhoid fever Typhoid fever, also known as typhoid, is a disease caused by '' Salmonella'' serotype Typhi bacteria. Symptoms vary from mild to severe, and usually begin six to 30 days after exposure. Often there is a gradual onset of a high fever over severa ...
contracted at the age of twelve, went on to have a distinguished career in virology. In 1926, he was invited to speak at a meeting organised by the Society of American Bacteriology where he said for the first time, "Viruses appear to be obligate parasites in the sense that their reproduction is dependent on living cells." The notion that viruses were particles was not considered unnatural and fitted in nicely with the
germ theory The germ theory of disease is the currently accepted scientific theory for many diseases. It states that microorganisms known as pathogens or "germs" can lead to disease. These small organisms, too small to be seen without magnification, invade h ...
. It is assumed that Dr. J. Buist of Edinburgh was the first person to see virus particles in 1886, when he reported seeing "micrococci" in vaccine lymph, though he had probably observed clumps of
vaccinia ''Vaccinia virus'' (VACV or VV) is a large, complex, enveloped virus belonging to the poxvirus family. It has a linear, double-stranded DNA genome approximately 190 kbp in length, which encodes approximately 250 genes. The dimensions of t ...
. In the years that followed, as optical microscopes were improved "inclusion bodies" were seen in many virus-infected cells, but these aggregates of virus particles were still too small to reveal any detailed structure. It was not until the invention of the electron microscope in 1931 by the German engineers
Ernst Ruska Ernst August Friedrich Ruska (; 25 December 1906 – 27 May 1988) was a German physicist who won the Nobel Prize in Physics in 1986 for his work in electron optics, including the design of the first electron microscope. Life and career Erns ...
(1906–1988) and
Max Knoll Max Knoll (17 July 1897 – 6 November 1969) was a German electrical engineer. Knoll was born in Wiesbaden and studied in Munich and at the Technical University of Berlin, where he obtained his doctorate in the Institute for High Voltage T ...
(1887–1969), that virus particles, especially
bacteriophage A bacteriophage (), also known informally as a ''phage'' (), is a duplodnaviria virus that infects and replicates within bacteria and archaea. The term was derived from "bacteria" and the Greek φαγεῖν ('), meaning "to devour". Bac ...
s, were shown to have complex structures. The sizes of viruses determined using this new microscope fitted in well with those estimated by filtration experiments. Viruses were expected to be small, but the range of sizes came as a surprise. Some were only a little smaller than the smallest known bacteria, and the smaller viruses were of similar sizes to complex organic molecules. In 1935, Wendell Stanley examined the tobacco mosaic virus and found it was mostly made of protein. In 1939, Stanley and Max Lauffer (1914) separated the virus into protein and
nucleic acid Nucleic acids are biopolymers, macromolecules, essential to all known forms of life. They are composed of nucleotides, which are the monomers made of three components: a 5-carbon sugar, a phosphate group and a nitrogenous base. The two main ...
, which was shown by Stanley's postdoctoral fellow Hubert S. Loring to be specifically RNA. The discovery of RNA in the particles was important because in 1928,
Fred Griffith Frederick Griffith (1877–1941) was a British bacteriologist whose focus was the epidemiology and pathology of bacterial pneumonia. In January 1928 he reported what is now known as Griffith's Experiment, the first widely accepted demonstratio ...
(–1941) provided the first evidence that its "cousin", DNA, formed
genes In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a ba ...
. In Pasteur's day, and for many years after his death, the word "virus" was used to describe any cause of infectious disease. Many
bacteriologist A bacteriologist is a microbiologist, or similarly trained professional, in bacteriology -- a subdivision of microbiology that studies bacteria, typically pathogenic ones. Bacteriologists are interested in studying and learning about bacteria, ...
s soon discovered the cause of numerous infections. However, some infections remained, many of them horrendous, for which no bacterial cause could be found. These agents were invisible and could only be grown in living animals. The discovery of viruses paved the way to understanding these mysterious infections. And, although
Koch's postulates Koch's postulates ( )"Koch"
''


Discovery

Bacteriophage A bacteriophage (), also known informally as a ''phage'' (), is a duplodnaviria virus that infects and replicates within bacteria and archaea. The term was derived from "bacteria" and the Greek φαγεῖν ('), meaning "to devour". Bac ...
s are the viruses that infect and replicate in bacteria. They were discovered in the early 20th century, by the English bacteriologist
Frederick Twort Frederick William Twort FRS (22 October 1877 – 20 March 1950) was an English bacteriologist and was the original discoverer in 1915 of bacteriophages (viruses that infect bacteria). He studied medicine at St Thomas's Hospital, London, was super ...
(1877–1950). But before this time, in 1896, the bacteriologist Ernest Hanbury Hankin (1865–1939) reported that something in the waters of the River Ganges could kill ''
Vibrio cholerae ''Vibrio cholerae'' is a species of Gram-negative, facultative anaerobe and comma-shaped bacteria. The bacteria naturally live in brackish or saltwater where they attach themselves easily to the chitin-containing shells of crabs, shrimps, and oth ...
'' – the cause of
cholera Cholera is an infection of the small intestine by some strains of the bacterium '' Vibrio cholerae''. Symptoms may range from none, to mild, to severe. The classic symptom is large amounts of watery diarrhea that lasts a few days. Vomiting an ...
. The agent in the water could be passed through filters that remove bacteria but was destroyed by boiling. Twort discovered the action of bacteriophages on
staphylococci ''Staphylococcus'' is a genus of Gram-positive bacteria in the family Staphylococcaceae from the order Bacillales. Under the microscope, they appear spherical ( cocci), and form in grape-like clusters. ''Staphylococcus'' species are facultati ...
bacteria. He noticed that when grown on nutrient agar some colonies of the bacteria became watery. He collected some of these watery colonies and passed them through a Chamberland filter to remove the bacteria and discovered that when the filtrate was added to fresh cultures of bacteria, they in turn became watery. He proposed that the agent might be "an amoeba, an ultramicroscopic virus, a living protoplasm, or an enzyme with the power of growth". Félix d'Herelle (1873–1949) was a mainly self-taught French-Canadian microbiologist. In 1917 he discovered that "an invisible antagonist", when added to bacteria on
agar Agar ( or ), or agar-agar, is a jelly-like substance consisting of polysaccharides obtained from the cell walls of some species of red algae, primarily from ogonori (''Gracilaria'') and "tengusa" (''Gelidiaceae''). As found in nature, agar i ...
, would produce areas of dead bacteria. The antagonist, now known to be a bacteriophage, could pass through a Chamberland filter. He accurately diluted a suspension of these viruses and discovered that the highest dilutions (lowest virus concentrations), rather than killing all the bacteria, formed discrete areas of dead organisms. Counting these areas and multiplying by the dilution factor allowed him to calculate the number of viruses in the original suspension. He realised that he had discovered a new form of virus and later coined the term "bacteriophage". Between 1918 and 1921 d'Herelle discovered different types of bacteriophages that could infect several other species of bacteria including ''Vibrio cholerae''. Bacteriophages were heralded as a potential treatment for diseases such as
typhoid Typhoid fever, also known as typhoid, is a disease caused by ''Salmonella'' serotype Typhi bacteria. Symptoms vary from mild to severe, and usually begin six to 30 days after exposure. Often there is a gradual onset of a high fever over several d ...
and
cholera Cholera is an infection of the small intestine by some strains of the bacterium '' Vibrio cholerae''. Symptoms may range from none, to mild, to severe. The classic symptom is large amounts of watery diarrhea that lasts a few days. Vomiting an ...
, but their promise was forgotten with the development of
penicillin Penicillins (P, PCN or PEN) are a group of β-lactam antibiotics originally obtained from '' Penicillium'' moulds, principally '' P. chrysogenum'' and '' P. rubens''. Most penicillins in clinical use are synthesised by P. chrysogenum usin ...
. Since the early 1970s, bacteria have continued to develop resistance to
antibiotic An antibiotic is a type of antimicrobial substance active against bacteria. It is the most important type of antibacterial agent for fighting bacterial infections, and antibiotic medications are widely used in the treatment and prevention ...
s such as
penicillin Penicillins (P, PCN or PEN) are a group of β-lactam antibiotics originally obtained from '' Penicillium'' moulds, principally '' P. chrysogenum'' and '' P. rubens''. Most penicillins in clinical use are synthesised by P. chrysogenum usin ...
, and this has led to a renewed interest in the use of bacteriophages to treat serious infections. 1920-1940: Early research D'Herelle travelled widely to promote the use of bacteriophages in the treatment of bacterial infections. In 1928, he became professor of biology at
Yale Yale University is a private research university in New Haven, Connecticut. Established in 1701 as the Collegiate School, it is the third-oldest institution of higher education in the United States and among the most prestigious in the wor ...
and founded several research institutes. He was convinced that bacteriophages were viruses despite opposition from established bacteriologists such as the Nobel Prize winner
Jules Bordet Jules Jean Baptiste Vincent Bordet (; 13 June 1870 – 6 April 1961) was a Belgian immunologist and microbiologist. The bacterial genus '' Bordetella'' is named after him. The Nobel Prize in Physiology or Medicine was awarded to him in 1919 fo ...
(1870–1961). Bordet argued that bacteriophages were not viruses but just
enzyme Enzymes () are proteins that act as biological catalysts by accelerating chemical reactions. The molecules upon which enzymes may act are called substrates, and the enzyme converts the substrates into different molecules known as products ...
s released from "lysogenic" bacteria. He said "the invisible world of d'Herelle does not exist". But in the 1930s, the proof that bacteriophages were viruses was provided by Christopher Andrewes (1896–1988) and others. They showed that these viruses differed in size and in their chemical and
serological Serology is the scientific study of serum and other body fluids. In practice, the term usually refers to the diagnostic identification of antibodies in the serum. Such antibodies are typically formed in response to an infection (against a given mic ...
properties. In 1940, the first
electron micrograph A micrograph or photomicrograph is a photograph or digital image taken through a microscope or similar device to show a magnified image of an object. This is opposed to a macrograph or photomacrograph, an image which is also taken on a mi ...
of a bacteriophage was published and this silenced sceptics who had argued that bacteriophages were relatively simple enzymes and not viruses. Numerous other types of bacteriophages were quickly discovered and were shown to infect bacteria wherever they are found. Early research was interrupted by
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the World War II by country, vast majority of the world's countries—including all of the great power ...
. d'Herelle, despite his Canadian citizenship, was interned by the
Vichy Government Vichy France (french: Régime de Vichy; 10 July 1940 – 9 August 1944), officially the French State ('), was the fascist French state headed by Marshal Philippe Pétain during World War II. Officially independent, but with half of its terr ...
until the end of the war.


Modern era

Knowledge of bacteriophages increased in the 1940s following the formation of the Phage Group by scientists throughout the US. Among the members were
Max Delbrück Max Ludwig Henning Delbrück (; September 4, 1906 – March 9, 1981) was a German–American biophysicist who participated in launching the molecular biology research program in the late 1930s. He stimulated physical scientists' interest int ...
(1906–1981) who founded a course on bacteriophages at
Cold Spring Harbor Laboratory Cold Spring Harbor Laboratory (CSHL) is a private, non-profit institution with research programs focusing on cancer, neuroscience, plant biology, genomics, and quantitative biology. It is one of 68 institutions supported by the Cancer Centers ...
. Other key members of the Phage Group included
Salvador Luria Salvador Edward Luria (August 13, 1912 – February 6, 1991) was an Italian microbiologist, later a Naturalized citizen of the United States#Naturalization, naturalized U.S. citizen. He won the Nobel Prize in Physiology or Medicine in 1969, with ...
(1912–1991) and
Alfred Hershey Alfred Day Hershey (December 4, 1908 – May 22, 1997) was an American Nobel Prize–winning bacteriologist and geneticist. He was born in Owosso, Michigan and received his B.S. in chemistry at Michigan State University in 1930 and his Ph.D. i ...
(1908–1997). During the 1950s, Hershey and Chase made important discoveries on the replication of DNA during their studies on a bacteriophage called T2. Together with Delbruck they were jointly awarded the 1969 Nobel Prize in Physiology or Medicine "for their discoveries concerning the replication mechanism and the genetic structure of viruses". Since then, the study of bacteriophages has provided insights into the switching on and off of genes, and a useful mechanism for introducing foreign genes into bacteria and many other fundamental mechanisms of
molecular biology Molecular biology is the branch of biology that seeks to understand the molecular basis of biological activity in and between cells, including biomolecular synthesis, modification, mechanisms, and interactions. The study of chemical and phys ...
.


Plant viruses

In 1882,
Adolf Mayer Adolf Eduard Mayer (9 August 184325 December 1942) was a German Agricultural chemistry, agricultural chemist whose work on Tobacco mosaic virus, tobacco mosaic disease played an important role in the discovery of tobacco mosaic virus and viruses ...
(1843–1942) described a condition of tobacco plants, which he called "mosaic disease" ("mozaïkziekte"). The diseased plants had
variegated Variegation is the appearance of differently coloured zones in the leaves and sometimes the stems and fruit of plants. Species with variegated individuals are sometimes found in the understory of tropical rainforests, and this habitat is the ...
leaves that were
mottle Mottle is a pattern of irregular marks, spots, streaks, blotches or patches of different shades or colours. It is commonly used to describe the surface of plants or the skin of animals. In plants, mottling usually consists of yellowish spots o ...
d. He excluded the possibility of a fungal infection and could not detect any bacterium and speculated that a "soluble, enzyme-like infectious principle was involved".Quoted in: He did not pursue his idea any further, and it was the filtration experiments of Ivanovsky and Beijerinck that suggested the cause was a previously unrecognised infectious agent. After tobacco mosaic was recognized as a virus disease, virus infections of many other plants were discovered. The importance of tobacco mosaic virus in the history of viruses cannot be overstated. It was the first virus to be discovered, and the first to be
crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macro ...
lised and its structure shown in detail. The first
X-ray diffraction X-ray crystallography is the experimental science determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to diffract into many specific directions. By measuring the angles ...
pictures of the crystallised virus were obtained by Bernal and Fankuchen in 1941. On the basis of her pictures,
Rosalind Franklin Rosalind Elsie Franklin (25 July 192016 April 1958) was a British chemist and X-ray crystallographer whose work was central to the understanding of the molecular structures of DNA (deoxyribonucleic acid), RNA (ribonucleic acid), viruses, ...
discovered the full structure of the virus in 1955. In the same year, Heinz Fraenkel-Conrat and Robley Williams showed that purified tobacco mosaic virus RNA and its coat protein can assemble by themselves to form functional viruses, suggesting that this simple mechanism was probably the means through which viruses were created within their host cells. By 1935, many plant diseases were thought to be caused by viruses. In 1922, John Kunkel Small (1869–1938) discovered that insects could act as vectors and transmit virus to plants. In the following decade many diseases of plants were shown to be caused by viruses that were carried by insects and in 1939, Francis Holmes, a pioneer in plant virology, described 129 viruses that caused disease of plants. Modern, intensive agriculture provides a rich environment for many plant viruses. In 1948, in Kansas, US, 7% of the wheat crop was destroyed by
wheat streak mosaic virus ''Wheat streak mosaic virus'' (WSMV) is a plant pathogenic virus of the family ''Potyviridae'' that infects plants in the family Poaceae, especially wheat (''Triticum Wheat is a grass widely cultivated for its seed, a cereal grain that is ...
. The virus was spread by mites called '' Aceria tulipae''. In 1970, the Russian plant virologist Joseph Atabekov discovered that many plant viruses only infect a single species of host plant. The
International Committee on Taxonomy of Viruses The International Committee on Taxonomy of Viruses (ICTV) authorizes and organizes the taxonomic classification of and the nomenclatures for viruses. The ICTV has developed a universal taxonomic scheme for viruses, and thus has the means to ap ...
now recognises over 900 plant viruses.


20th century

By the end of the 19th century, viruses were defined in terms of their
infectivity In epidemiology, infectivity is the ability of a pathogen to establish an infection. More specifically, infectivity is a pathogen's capacity for horizontal transmission — that is, how frequently it spreads among hosts that are not in a parent ...
, their ability to be filtered, and their requirement for living hosts. Up until this time, viruses had only been grown in plants and animals, but in 1906, Ross Granville Harrison (1870–1959) invented a method for growing tissue in
lymph Lymph (from Latin, , meaning "water") is the fluid that flows through the lymphatic system, a system composed of lymph vessels (channels) and intervening lymph nodes whose function, like the venous system, is to return fluid from the tissues ...
, and, in 1913, E Steinhardt, C Israeli, and RA Lambert used this method to grow
vaccinia ''Vaccinia virus'' (VACV or VV) is a large, complex, enveloped virus belonging to the poxvirus family. It has a linear, double-stranded DNA genome approximately 190 kbp in length, which encodes approximately 250 genes. The dimensions of t ...
virus in fragments of guinea pig corneal tissue. In 1928, HB and MC Maitland grew vaccinia virus in suspensions of minced hens' kidneys. Their method was not widely adopted until the 1950s, when
poliovirus A poliovirus, the causative agent of polio (also known as poliomyelitis), is a serotype of the species '' Enterovirus C'', in the family of '' Picornaviridae''. There are three poliovirus serotypes: types 1, 2, and 3. Poliovirus is composed of ...
was grown on a large scale for vaccine production. In 1941–42,
George Hirst George Herbert Hirst (7 September 1871 – 10 May 1954) was a professional English cricketer who played first-class cricket for Yorkshire County Cricket Club between 1891 and 1921, with a further appearance in 1929. One of the best all-r ...
(1909–94) developed assays based on haemagglutination to quantify a wide range of viruses as well as virus-specific antibodies in serum.


Influenza

Although the
influenza virus ''Orthomyxoviridae'' (from Greek ὀρθός, ''orthós'' 'straight' + μύξα, ''mýxa'' 'mucus') is a family of negative-sense RNA viruses. It includes seven genera: ''Alphainfluenzavirus'', ''Betainfluenzavirus'', '' Gammainfluenzavirus'', ' ...
that caused the 1918–1919 influenza pandemic was not discovered until the 1930s, the descriptions of the disease and subsequent research has proved it was to blame. The pandemic killed 40–50 million people in less than a year, but the proof that it was caused by a virus was not obtained until 1933. ''
Haemophilus influenzae ''Haemophilus influenzae'' (formerly called Pfeiffer's bacillus or ''Bacillus influenzae'') is a Gram-negative, non-motile, coccobacillary, facultatively anaerobic, capnophilic pathogenic bacterium of the family Pasteurellaceae. The bact ...
'' is an opportunistic bacterium which commonly follows influenza infections; this led the eminent German bacteriologist Richard Pfeiffer (1858–1945) to incorrectly conclude that this bacterium was the cause of influenza. A major breakthrough came in 1931, when the American pathologist Ernest William Goodpasture grew influenza and several other viruses in fertilised chickens' eggs. Hirst identified an enzymic activity associated with the virus particle, later characterised as the
neuraminidase Exo-α-sialidase (EC 3.2.1.18, sialidase, neuraminidase; systematic name acetylneuraminyl hydrolase) is a glycoside hydrolase that cleaves the glycosidic linkages of neuraminic acids: : Hydrolysis of α-(2→3)-, α-(2→6)-, α-(2→8)- glyc ...
, the first demonstration that viruses could contain enzymes.
Frank Macfarlane Burnet Sir Frank Macfarlane Burnet, (3 September 1899 – 31 August 1985), usually known as Macfarlane or Mac Burnet, was an Australian virologist known for his contributions to immunology. He won a Nobel Prize in 1960 for predicting acquired immune ...
showed in the early 1950s that the virus recombines at high frequencies, and Hirst later deduced that it has a segmented genome.


Poliomyelitis

In 1949,
John F. Enders John Franklin Enders (February 10, 1897 – September 8, 1985) was an American biomedical scientist and Nobel Laureate. Enders has been called "The Father of Modern Vaccines." Life and education Enders was born in West Hartford, Connecticut on ...
(1897–1985) Thomas Weller (1915–2008), and
Frederick Robbins Frederick Chapman Robbins (August 25, 1916 – August 4, 2003) was an American pediatrician and virologist. He was born in Auburn, Alabama, and grew up in Columbia, Missouri, attending David H. Hickman High School. He received the Nobel Prize in P ...
(1916–2003) grew polio virus for the first time in cultured human embryo cells, the first virus to be grown without using solid animal tissue or eggs. Infections by poliovirus most often cause the mildest of symptoms. This was not known until the virus was isolated in cultured cells and many people were shown to have had mild infections that did not lead to poliomyelitis. But, unlike other viral infections, the incidence of polio – the rarer severe form of the infection – increased in the 20th century and reached a peak around 1952. The invention of a
cell culture Cell culture or tissue culture is the process by which cells are grown under controlled conditions, generally outside of their natural environment. The term "tissue culture" was coined by American pathologist Montrose Thomas Burrows. This tec ...
system for growing the virus enabled
Jonas Salk Jonas Edward Salk (; born Jonas Salk; October 28, 1914June 23, 1995) was an American virologist and medical researcher who developed one of the first successful polio vaccines. He was born in New York City and attended the City College of New ...
(1914–1995) to make an effective
polio vaccine Polio vaccines are vaccines used to prevent poliomyelitis (polio). Two types are used: an inactivated poliovirus given by injection (IPV) and a weakened poliovirus given by mouth (OPV). The World Health Organization (WHO) recommends all chi ...
.


Epstein–Barr virus

Denis Parsons Burkitt Denis Parsons Burkitt, MD, FRCS(Ed), FRS (28 February 1911 – 23 March 1993) was an Irish surgeon who made significant advances in health, such as the etiology of a pediatric cancer, now called Burkitt's lymphoma, and the finding that rates ...
(1911–1993) was born in Enniskillen, County Fermanagh, Ireland. He was the first to describe a type of cancer that now bears his name
Burkitt's lymphoma Burkitt lymphoma is a cancer of the lymphatic system, particularly B lymphocytes found in the germinal center. It is named after Denis Parsons Burkitt, the Irish surgeon who first described the disease in 1958 while working in equatorial Africa. ...
. This type of cancer was endemic in equatorial Africa and was the commonest malignancy of children in the early 1960s. In an attempt to find a cause for the cancer, Burkitt sent cells from the tumour to
Anthony Epstein Sir Michael Anthony Epstein (born 18 May 1921) is a British pathologist and academic. He is one of the discoverers of the Epstein–Barr virus, along with Yvonne Barr and Bert Achong. Personal life Epstein was born on 18 May 1921, and educ ...
(b. 1921) a British virologist, who along with Yvonne Barr and
Bert Achong Bert Geoffrey Achong (6 December 1928 – 28 November 1996) was a Trinidadian-born pathologist known for co-discovering the Epstein–Barr virus through use of electron microscopy. Career Achong was born in Trinidad and Tobago and was of Chin ...
(1928–1996), and after many failures, discovered viruses that resembled herpes virus in the fluid that surrounded the cells. The virus was later shown to be a previously unrecognised herpes virus, which is now called
Epstein–Barr virus The Epstein–Barr virus (EBV), formally called ''Human gammaherpesvirus 4'', is one of the nine known human herpesvirus types in the herpes family, and is one of the most common viruses in humans. EBV is a double-stranded DNA virus. It is ...
. Surprisingly, Epstein–Barr virus is a very common but relatively mild infection of Europeans. Why it can cause such a devastating illness in Africans is not fully understood, but reduced immunity to virus caused by
malaria Malaria is a mosquito-borne infectious disease that affects humans and other animals. Malaria causes symptoms that typically include fever, tiredness, vomiting, and headaches. In severe cases, it can cause jaundice, seizures, coma, or death. ...
might be to blame. Epstein–Barr virus is important in the history of viruses for being the first virus shown to cause cancer in humans.


Late 20th and early 21st century

The second half of the 20th century was the golden age of virus discovery and most of the 2,000 recognised species of animal, plant, and bacterial viruses were discovered during these years. In 1946,
bovine virus diarrhea Bovine viral diarrhea (BVD), bovine viral diarrhoea (UK English) or mucosal disease, and previously referred to as bovine virus diarrhea (BVD), is an economically significant disease of cattle that is found in the majority of countries throughout ...
was discovered, which is still possibly the most common pathogen of cattle throughout the world and in 1957, equine arterivirus was discovered. In the 1950s, improvements in virus isolation and detection methods resulted in the discovery of several important human viruses including
varicella zoster virus Varicella-zoster virus (VZV), also known as human herpesvirus 3 (HHV-3, HHV3) or ''Human alphaherpesvirus 3'' (taxonomically), is one of nine known herpes viruses that can infect humans. It causes chickenpox (varicella) commonly affecting chil ...
, the paramyxoviruses, – which include
measles Measles is a highly contagious infectious disease caused by measles virus. Symptoms usually develop 10–12 days after exposure to an infected person and last 7–10 days. Initial symptoms typically include fever, often greater than , cough, ...
virus, and
respiratory syncytial virus Respiratory syncytial virus (RSV), also called human respiratory syncytial virus (hRSV) and human orthopneumovirus, is a common, contagious virus that causes infections of the respiratory tract. It is a negative-sense, single-stranded RNA virus. ...
– and the rhinoviruses that cause the
common cold The common cold or the cold is a viral infectious disease of the upper respiratory tract that primarily affects the respiratory mucosa of the nose, throat, sinuses, and larynx. Signs and symptoms may appear fewer than two days after expos ...
. In the 1960s more viruses were discovered. In 1963, the
hepatitis B virus ''Hepatitis B virus'' (HBV) is a partially double-stranded DNA virus, a species of the genus '' Orthohepadnavirus'' and a member of the '' Hepadnaviridae'' family of viruses. This virus causes the disease hepatitis B. Disease Despite there b ...
was discovered by
Baruch Blumberg Baruch Samuel Blumberg (July 28, 1925 April 5, 2011), known as Barry Blumberg, was an American physician, geneticist, and co-recipient of the 1976 Nobel Prize in Physiology or Medicine (with Daniel Carleton Gajdusek), for his work on the hepat ...
(b. 1925).
Reverse transcriptase A reverse transcriptase (RT) is an enzyme used to generate complementary DNA (cDNA) from an RNA template, a process termed reverse transcription. Reverse transcriptases are used by viruses such as HIV and hepatitis B to replicate their genom ...
, the key enzyme that retroviruses use to
translate Translation is the communication of the meaning of a source-language text by means of an equivalent target-language text. The English language draws a terminological distinction (which does not exist in every language) between ''transl ...
their RNA into DNA, was first described in 1970, independently by Howard Temin and
David Baltimore David Baltimore (born March 7, 1938) is an American biologist, university administrator, and 1975 Nobel laureate in Physiology or Medicine. He is President Emeritus and Distinguished Professor of Biology at the California Institute of Tec ...
(b. 1938). This was important to the development of
antiviral drug Antiviral drugs are a class of medication used for treating viral infections. Most antivirals target specific viruses, while a broad-spectrum antiviral is effective against a wide range of viruses. Unlike most antibiotics, antiviral drugs do n ...
s – a key turning-point in the history of viral infections. In 1983,
Luc Montagnier Luc Montagnier (; , ; 18 August 1932 – 8 February 2022) was a French virologist and joint recipient, with and , of the 2008 Nobel Prize in Physiology or Medicine for his discovery of the human immunodeficiency virus (HIV). He worked as a r ...
(b. 1932) and his team at the
Pasteur Institute The Pasteur Institute (french: Institut Pasteur) is a French non-profit private foundation dedicated to the study of biology, micro-organisms, diseases, and vaccines. It is named after Louis Pasteur, who invented pasteurization and vacc ...
in France first isolated the retrovirus now called HIV. In 1989 Michael Houghton's team at
Chiron Corporation Chiron Corporation ( ) was an American multinational biotechnology firm founded in 1981, based in Emeryville, California, that was acquired by Novartis on April 20, 2006. It had offices and facilities in eighteen countries on five continents. ...
discovered
hepatitis C Hepatitis C is an infectious disease caused by the hepatitis C virus (HCV) that primarily affects the liver; it is a type of viral hepatitis. During the initial infection people often have mild or no symptoms. Occasionally a fever, dark urine, ...
. New viruses and strains of viruses were discovered in every decade of the second half of the 20th century. These discoveries have continued in the 21st century as new viral diseases such as
SARS Severe acute respiratory syndrome (SARS) is a viral respiratory disease of zoonotic origin caused by the severe acute respiratory syndrome coronavirus (SARS-CoV or SARS-CoV-1), the first identified strain of the SARS coronavirus species, ''seve ...
and
nipah virus Nipah virus, scientific name ''Nipah henipavirus'', is a bat-borne virus that causes Nipah virus infection in humans and other animals, a disease with a high mortality rate. Numerous disease outbreaks caused by Nipah virus have occurred in Sou ...
have emerged. Despite scientists' achievements over the past one hundred years, viruses continue to pose new threats and challenges.


See also

*
List of viruses This is an index of lists of virus taxa. By taxonomic rank * List of higher virus taxa, i.e. all taxa above the rank of family * List of virus families and subfamilies * List of virus genera :''This is a list of genera of biological viruses. See ...


References

{{History of medicine