The following text may or may not appear in a book of some kind in the future. However, I thought I may as well share it – both for general education purposes, as well as for comment. Enjoy!
A Short History of the Discovery of Viruses
While people were aware of diseases of both humans and animals now known to be caused by viruses many hundreds of years ago, the concept of a virus as a distinct entity dates back only to the very late 1800s. Although the term had been used for many years previously to describe disease agents, the word “virus” comes from a Latin word simply meaning “slimy fluid”. This discovery, along with many that followed later, was made possible by the development of new technology. Though this simple invention essentially enabled the establishment of a whole new science – virology – the continued development of the discipline required a string of technical developments, which I will highlight throughout this piece.
The Magic Filter
The invention that allowed viruses to be discovered at all was the Chamberland-Pasteur filter. This was developed in 1884 in Paris by Charles Chamberland, who worked with Louis Pasteur. It consisted of unglazed porcelain “candles”, with pore sizes of 0.1 – 1 micron (100 – 1000 nm), which could be used to completely remove all bacteria or other cells known at the time from a liquid suspension.
As the first in what was to be an interesting succession of events, Adolph Mayer from Germany, working in Holland in 1886, showed that the “mosaic disease” of tobacco could be transmitted to other plants by rubbing a liquid extract, filtered through paper, from an infected plant onto the leaves of a healthy plant. However, he came to the conclusion it must be a bacterial disease.
The first use of porcelain filters to characterize what we now know to be a virus was reported by Dmitri Ivanowski in St Petersburg in Russia, in 1892. He had used a filter candle on an infectious extract of tobacco plants with mosaic disease, and shown that it remained infectious: however, he concluded the agent was either a toxin or bacterial in nature.
The Dutch scientist Martinus van Beijerinck in 1898 described how he did similar experiments with bacteria-free extracts, but made the conceptual leap and described the agent of mosaic disease of tobacco as a “contagium vivum fluidum”, or living contagious fluid. The extract was completely sterile, could be kept for years, but remained infectious. The term virus was later used to describe such fluids, also called “filterable agents”, which were thought to contain no particles. The virus causing mosaic disease is now known as Tobacco mosaic virus (TMV).
The second virus discovered was what is now known as Foot and mouth disease virus (FMDV) of farm and other animals, in 1899 by the German scientists Friedrich Loeffler and Paul Frosch. Again, their “sterile” filtered liquid proved infectious in calves, providing the first proof of viruses infecting animals. In fact, some believe that the true discoverers of viruses were these two scientists, as they concluded the infectious agent was a tiny particle, and was not liquid.
In the same year – 1898 – G Sanarelli, working in Uruguay, described the smallpox virus relative and tumour-causing myxoma virus of rabbits as a virus – but on the basis of sterilisation by centrifugation rather than filtration.
The first human virus described was the agent which causes yellow fever: this was discovered and reported in 1901 by the US Army physician Walter Reed, after pioneering work in Cuba by Carlos Finlay proving that mosquitoes transmitted the deadly disease. The agent became the subject of intense study because, in the recent Spanish-American war in Cuba, about 13 times as many soldiers died of yellow fever as died from wounds. The subsequent eradication of mosquitoes in Panama is probably what allowed the completion of the Panama Canal – stalled because of the death rate among workers from the deadly disease.
A finding that was later to have great importance in veterinary virology was the discovery by Maurice Nicolle and Adil Mustafa (also known as Adil-Bey), in Turkey in 1902, that rinderpest or cattle plague was caused by a virus. This had been for several centuries the worst animal disease known worldwide in terms of mortality: for example, an epizootic or animal epidemic in Africa in the 1890s that had started in what is now Ethiopia in 1887 from cattle imported from Asia, had spread throughout the continent by 1897, and killed 80-90% of the cattle and a large proportion of susceptible wild animals in southern Africa. Many thousands of people died of starvation as a result. The virus is, incidentally, only the second to have ever been eradicated – nearly 100 years after its discovery.
Viruses and Vaccines
Sir Arnold Theiler, a Swiss-born veterinarian working in South Africa, had developed a crude vaccine against rinderpest by 1897, without knowledge of the nature of the agent: this consisted of blood from an infected animal, injected with serum from one that had recovered. This risky mixture worked well enough, however, to eradicate the disease in the region. He went on to do the same thing successfully for African horsesickness virus and others in an institute (Onderstepoort Veterinary Institute) that still works on the virus.
The description in Annales de l’Institut Pasteur by Remlinger and Riffat-Bay in 1903 of the agent of rabies as a “filterable virus was the culmination of many years of distinguished work in France on the virus, started by Louis Pasteur himself. While Remlinger credited Pasteur with having the notion in 1881 that rabies virus was an ultramicroscopic particle, the fact is that Pasteur and Emile Roux had also, in 1885, effectively made a vaccine against rabies by use of dried infected rabbit spinal cords, without any knowledge of what the agent was.
The viral nature of many disease agents started to be made evident around this time, as more researchers started investigating known diseases. In 1906, Adelchi Negri – who had previously discovered the Negri bodies in cells infected with rabies virus – showed that vaccinia virus, the vaccine for the dreaded smallpox caused by variola virus, was filterable. This was the final step in a long series of discoveries around smallpox, that started with Edward Jenner’s use of what was supposedly cowpox, but may have been horsepox virus to protect people from the disease in 1796.
Viruses, Humans and Cancer
In 1908, Oluf Bang and Vilhelm Ellerman in Denmark were the first to associate a virus with leukaemia: they successfully used a cell-free filtrate from chickens with avian leukosis to transmit the disease to healthy chickens.
An important development in human virology 1908 was the finding by Karl Landsteiner and Erwin Popper in Germany that poliomyelitis or infantile paralysis in humans was caused by a virus: they proved this by injecting a cell-free extract of a suspension of spinal cord from a child who had died of the disease, into monkeys, and showing that they developed symptoms of the disease.
The first solid tumour-causing virus, or virus associated with cancer, was found by Peyton Rous in the USA in 1911. He showed that chicken sarcomas, or solid connective tissue tumours, could be transmitted by grafting, but also that a filterable or cell-free agent extracted from a sarcoma was infectious. The virus was named for him as Rous sarcoma virus, and is now known to be a “retrovirus”, in the same virus family as HIV.
Eaters of Bacteria: The Phages
Two independent investigations led to the important discovery of viruses that infect bacteria: in 1915, Frederick Twort in the UK accidentally found a filterable agent that caused the bacteria he was growing to lyse, or burst open. While he was not sure whether or not it was a virus, Félix d’Hérelle in Paris published in 1917 that he had discovered a virus that lysed a bacterial agent he was culturing that caused dysentery, or diarrhoea. He named the virus “bacteriophage”, or eater of bacteria, derived from the Greek term “phagein”, meaning to eat.
The discovery of bacteriophages was a landmark in the history of virology, as it meant that for the first time it was relatively easy to work with viruses: many kinds of bacteria could be grown in solid or liquid culture quite easily, and the life cycle of the viruses could be studied in detail.
Interestingly, and as reported in ViroBlogy previously, “…the first discovery of phages was probably described by a gentleman named M. Hankin, in 1896 in Annales de l’Institut Pasteur: he showed that river water downstream of cholera-infested towns on the Jumma river in India contained no viable Cholera vibrio – and that this was a reliable property of the water.”
The Spanish Flu
Possibly the worst human plague the world has ever seen swept across the planet between 1918 and 1922: this was known as the Spanish Flu, from where it was first properly reported, and it went on to kill more than 50 million people all over the world. We now know it to have been H1N1 influenza type A: modern reconstruction of the virus from archived tissue samples and frozen bodies found in permafrost has shown it probably jumped directly into humans from birds.
Most medical authorities at the time thought the disease was caused by bacteria – however, MJ Dujarric de la Rivière, and Charles Nicolle – brother of Maurice – and Charles Lebailly in France, separately proposed in 1918 that the causative agent was a virus, based on properties of infectious extracts from diseased patients. Specifically, Nicolle and Lebailly found that the infectious agent was filterable, not present in the blood of an infected monkey, and caused disease in human volunteers. However, many scientists still doubted that influenza was a viral disease – and most people seem to accept that the virus was only discovered in the 1930s.
Translation of this passage (courtesy of Mrs Francoise Williamson):
1⁰ The bronchial expectoration of people suffering from flu, collected during the acute period, is virulent.
2⁰ The monkey (M. cynomolgus) is sensitive to the virus by sub-conjunctival and nasal inoculation.
3⁰ The flu agent is a filterable organism. The inoculation of the filtrate has indeed reproduced the illness in two of the people injected subcutaneously; on the other hand when given intravenously it appears to be ineffective. (two failures out of two tries).
4⁰ It is possible that the influenza virus does not occur in the patient’s blood. The blood of a monkey with influenza, inoculated subcutaneously, did not infect man; the negative blood result of subject 2 at D, is however, not convincing, the blood route seeming to be ineffective for the flu virus transmission.”
Other agents of other diseases were found to be “filterable viruses” in the 1920s, including yellow fever virus by Adrian Stokes in 1927, in Ghana. Indeed, the US bacteriologist and virologist Thomas Rivers in 1926 counted some sixty-five disease agents that had been identified as viruses.
Mouse Brains and Viruses
Another in a chain of related discoveries was the one by Howard Andervost, at Harvard University in 1929, who showed that human herpes simplex virus could be cultured by injection into the brains of live mice.
This led to the demonstration in 1930 by the South African-born Max Theiler – son of Sir Arnold – also at Harvard, that yellow fever virus could be similarly cultured: this allowed much easier handling of the virus, which until then had to be injected into monkeys in order to multiply it in their livers. In addition, it allowed the development of attenuated or weakened strains of virus, by him and in parallel by a French laboratory, by serial passage or repeated transmission of the virus between mice. It also allowed the successful animal testing of vaccine candidates, and of protective antisera, for which Theiler was awarded the Nobel Prize in 1951.
Until 2008, this was the first and only recognition of virus vaccine work by the Nobel Foundation.
A consequence of this work was the landmark in medical virology that was the development of human vaccines against yellow fever virus, by Wilbur Sawyer in the USA in 1931: this followed on Theiler’s mouse work in using brain-cultured virus plus human immune serum from recovered patients to immunize humans – very similar to Theiler Senior’s strategy with rinderpest, more than thirty years later.
Copyright Edward P Rybicki and Russell Kightley, February 2012, except where otherwise noted.
Tags: avian leukosis, bacteriophage, Chamberland filter, foot and mouth disease, history, history of viruses, Polio, poliomyelitis, rinderpest, Rous sarcoma, smallpox, tobacco mosaic, virus, yellow fever