Virology

Virology in Historical Perspective

by Lise Wilkinson
 

If the history of virology is circumscribed as a twentieth century sequence, comprising studies that make up the increasingly complex and sophisticated science of virology practised today in specialist laboratories around the world, viruses and virus diseases have been with the human race, as perennial threats of plagues and pestilence, for millennia.

One virus disease, rabies, in humans and dogs, is easily recognized in classical texts, from the Greek of Aristotle (384–322 bc) to the Latin of Celsus (fl c. ad25), who even introduced the term virus, Latin for ‘poison’ or ‘slimy liquid’. The terrifying manifestations and the inevitable fatality of the frank disease in humans has earned it much attention from writers and medical philosophers through the centuries; out of all proportion it may be said to its ravages in terms of human lives lost, which are slight when compared with the major scourges of humankind. At the other end of the scale, in terms of impact on medieval communities and history of the Western world in general, smallpox is equalled only by the bacterial disease bubonic plague; together they played a major role for popular acceptance of the principle of disease transmissibility from the sixteenth to the eighteenth centuries.

The first indications that there were infectious entities even smaller than and perhaps somehow different from the bacteria seen, described and defined by the schools of Robert Koch and Louis Pasteur in the second half of the nineteenth century, came to the fore in 1892, when the young Russian botanist D. I. Ivanovski (1864–1920) published a report on the tobacco mosaic disease decimating Russian crops during the 1880s and 1890s. He believed the disease to be of bacterial aetiology; but unable to isolate and cultivate a microbe, he suggested a bacterial toxin as the cause of the disease (the bacterial toxin of diphtheria had been discovered four years earlier at the Institut Pasteur in Paris).

In the late 1890s, and into the turn of the century, what came to be labelled ‘filterable viruses’ or ‘invisible viruses’ (throughout the nineteenth century ‘virus’, in France in particular, had been used as a blanket term for the ‘new’ infectious agents) were identified in increasing numbers. In 1897–1898 in Delft, W. M. Beijerinck (1851–1931), a former student of Adolf Mayer in Wageningen, where Mayer had also been interested in tobacco mosaic disease in the 1880s, elaborated experiments on the filterability of the agent, with more far-reaching results and a very different, more constructive, interpretation. In Berlin, also in 1897–1898, F. Loeffler and P. Frosch showed the agent of foot-and-mouth disease in cattle to be ‘filterable’; but as faithful followers of Koch, they merely assumed it to be a very small bacterium. W. Reed and J. Carroll, having confirmed mosquito (Aëdes aegypti) transmission of yellow fever in Havana at the turn of the century, went on to show the agent's filterability. The filterability of rabies virus was finally proved by Paul Remlinger in 1903, of fowl plague virus by Eugenio Centanni in 1901, and of African horse sickness by John M'Fadyean in 1900. The virus of myxomatosis was described by Giuseppe Sanarelli as ‘invisible’ in 1898.

Among this growing list, Beijerinck's initial experiments, and his interpretation of the results, deserves most attention. For he was not content merely to label the agent ‘filterable’ and ‘invisible’; he allowed himself further speculation on the nature of the ‘non-particulate’ infective ‘organism’ in a way which, although impossible to prove at the time, anticipated results concerning the nature of viruses half a century later. Beijerinck labelled the putative agent at the centre of his research a ‘Contagium vivum fluidum’. It was perhaps not a felicitous choice; his interpretation fed the disbelief and misunderstanding of his opponents, who included all but the most unorthodox of contemporary microbiologists. Based on early discussions in student days with his friend Jan van't Hoff, who was to make history in stereochemistry, he concluded that the agent must be a ‘soluble’ molecule rather than a ‘particulate’ substance suspended in surrounding fluids: in fact, a possibly water-soluble molecule, able to replicate, but only when ‘incorporated into the living protoplasm of the cell, into whose reproduction it is, in a manner of speaking, passively drawn’. It was a conclusion far ahead of its time: not until the second half of the century would work on the same virus of tobacco mosaic, and on bacteriophages, by then supported by advances in methodology and technology, prove how right Beijerinck had been in his ‘improbably wild’ speculation.

The early decades of the twentieth century saw few advances in research on ‘filterable viruses’, except for the steady addition to the numbers of known pathogens small enough to pass through bacterial filters without losing infectivity, and so to be classed as ‘filterable’, or indeed as ‘invisible’ in the microscopes of the time. The most advanced views of pathologists, in an age with scant knowledge of the nature and structure of protein molecules, described them as consisting of ‘colloid globulin’. One development, however, took place during the years of World War I; its importance would only be realized to its full extent many years later. It was the discovery of bacteriophage, the bacterial viruses, by F. W. Twort at the Brown Institution in London in 1915 and, whether independently or not, by the Canadian born Félix d'Herelle of the Institut Pasteur in Paris in 1917. They both observed the lysis of intact bacterial cultures by ‘invisible microbes’, later referred to as the Twort–d'Herelle phenomenon, and named by d'Herelle in his classic work first published in 1921, The Bacteriophage. From the beginning both Twort and d'Herelle hoped for therapeutic use of specific bacteriophage in the battle against specific bacterial diseases. At the time, it appeared to be a vain hope, not justified in practice; but not before, as early as 1925, it found its way into the literature of the period when Sinclair Lewis's Martin Arrowsmith disastrously failed to control a plague epidemic by means of bacteriophage. In the last decade of the twentieth century there are some indications that phages in the end might be of use against ‘superbugs’, resistant to known antibiotics.

Within the scientific community, others were not slow to see the wider implications of the discovery of phage. The geneticist H. J. Muller (1890–1967) was the first to observe the possibility of an analogy between bacteriophage and gene, and hence to anticipate the future importance of phage in the study of genetics. And Beijerinck, who had not added to his writings on tobacco mosaic virus since the turn of the century, wrote in 1922: ‘The dialysis test shows in my opinion very clearly that Bacteriophagus is of the same order of magnitude as a molecule of protein, and that the term “contagium vivum fluidum” which I long ago used of the virus of tobacco mosaic disease, is a fitting one.

With the discovery of bacteriophage there came a number of other developments in the 1920s, which were to be of particular importance for definitive studies of viruses, and later to be closely linked to parallel attempts to elucidate genetic determination and mechanisms, centred around the work of the physical chemist Max Delbrück (1906–1981) and of the Italian-American medical biologist Salvador Luria (1912–1991). Together they founded the ‘phage group’ and laid the foundations for the American school of molecular genetics – and with it the whole enormously influential movement towards molecular biology as it evolved before, during and after World War II. Those developments, and virus research in general, depended on advances in methodology and technology: the ultracentrifuge introduced by T. Svedberg and R. Fåhraeus in 1926 became an immensely valuable tool in difficult filtration experiments; and the development of the electron microscope in the 1930s began to facilitate determination of size and structure of bacteriophages and other viruses. The brick-shaped pox viruses were established at the head of any table recording sizes of viruses, with diameters of 250–300 nm; the arbovirus of yellow fever, transmitted by mosquitoes, near the lower limit at 17–28 nm by filtration, 29–31 nm by centrifugation.

With regard to structure, the use of electron microscopes began to reveal just how great were the differences between individual viruses, and presented possibilities (other than clinical) of constructing a systematic classification, adding to the fundamental division into RNA and DNA viruses further basic criteria concerned with their cubical or helical symmetry in arrangement of protein subunits, and with presence or absence of an outer envelope around a more rigid inner structure. Structural studies again began with tobacco mosaic virus, carried out by electron microscope pioneers H. Ruska, E. Pfankuch and G. A. Kausche in 1939–1940, before they turned to bacteriophage. At the same time, the phage group used a newly installed electron microscope at the Marine Biological Laboratory at Wood's Hole, Massachusetts, to explore questions concerning ways of entry of virus into the host cell prior to replication, and the overall nature of phage replication (Wood's Hole was affectionately known as ‘the biologists' summer camp’; the main centre for the phage group was at Cold Spring Harbor on Long Island Sound). The work of Delbrück, Luria, and their colleagues in the phage group laid the foundations for a deeper understanding of (a) the pathogenesis of virus infections, and (b) the mechanisms of lysogeny, for so long the province of Eugene and Elisabeth Wollman (both died after deportation to a German concentration camp during World War II), and later of André Lwoff (1902–1994), all of the Institut Pasteur, Paris. In addition, studies by the phage group further developed the suggestions concerning analogies between viruses and genes first made by H. J. Muller in the 1920s, and to the whole emerging subject of molecular biology.

Better understanding of pathogenicity and clinical features of the many important virus diseases of humans and domestic animals developed in parallel with advances in theoretical and experimental virology. The term ‘virology’ became established in its own right, no longer just a subdivision of bacteriology, gradually throughout the 1930s. After World War II, the first textbook, S. E. Luria's General Virology, was published in 1953, and the first issue of the journal Virology appeared in 1955.

Examples of Important Virus Diseases, Their Individual Histories, and Efforts to Control Them

Smallpox

Historically, smallpox and other ‘eruptive fevers’, not always easily distinguished in the past, have been at the centre of many of the great epidemics influencing population statistics and demography for centuries past. From the time of Rhazes's Treatise on the smallpox and measles (tenth century) measles has been described as a separate entity, although sometimes regarded in early literature as a milder or occasionally more virulent form of smallpox, until the work of Enlightenment physicians in the eighteenth century. At that time severe smallpox epidemics in Britain and on the European continent were reflected copiously in the literature of the time, with much emphasis on results of inoculation practices first introduced in Britain by Emanuel Timone at the Royal Society in 1714, and more publicly by Lady Mary Wortley Montagu from 1721 onwards; in Venice a treatise by G. Pylarino appeared in 1715, and in all these cases the procedure was based on the Middle Eastern pattern of ‘engrafting’ as practised in Constantinople. Catherine the Great took an interest in the practice of inoculation – the deliberate introduction of ‘lymph’ from mild cases of smallpox into healthy children and adults to prevent later severe cases. She herself was inoculated by Thomas Dimsdale in 1768.

In France, however, there was resistance to the practice, in spite of recommendation by Voltaire, who had himself suffered an attack of smallpox in 1723, until the death of Louis XV from the disease in 1774 caused the public and the authorities to view the procedure in a more favourable light. Two decades later Edward Jenner introduced cowpox vaccination against smallpox, and with it a new era which towards the end of the nineteenth century would see an accelerating development and use of vaccines against a number of diseases caused by bacteria and by ‘filterable’ viruses. Jenner's development of cowpox vaccination was a successful outcome of a purely empirical approach by an observant eighteenth-century doctor, with no taste for experimentation but favoured by a good deal of luck and the possession of common sense. Although Thomas Jefferson's prophecy in 1806 that Jenner's vaccine would ensure that ‘hellip Future nations will know by history only that the loathsome smallpox has existed’ was wildly premature, Jenner's system of vaccination – the variolae vaccinae – did in the end clear the world of smallpox, if not until 1979 when the World Health Organization (WHO), after a final campaign, could declare the disease eradicated – the first, and so far the only, example of a deliberate, and ultimately successful, attempt at global eradication of an infectious disease.

Measles

Measles, on the other hand, one of the most important and severe of childhood virus diseases, has been brought under control in the Western world, but remains a major threat in developing countries. A satisfactory vaccine was developed by J. F. Enders and his group at Harvard Medical School as an extension of his tissue culture techniques when applied to virology: he successfully adapted Alexis Carrell's much earlier method for growing cells in slowly rolling tubes. Enders' successful measles vaccine proved its worth in clinical trials and has been used in the USA and elsewhere in the West since 1961. Recent public doubts concerning the safety of the combined measles–mumps–rubella vaccine in Britain remain unproven, and it is to be hoped will not interfere with present policies of prevention.

Rabies

If Jenner's development of cowpox vaccine against smallpox was a wholly fortuitous first use of the principle of attenuation whose successful conclusion owed much, if not all, to luck, the use of attenuation as a tool in developing vaccines against known bacteria and viruses in the 1880s by Pasteur and his staff owed little to chance and much to experimentation, carefully thought out and planned. Admittedly, the first observation was fortuitous: a virulent strain of fowl cholera was left by chance longer than intended (as with Fleming's pencillin half a century later); when later re-examined it was found on inoculation to protect fowl against infection rather than produce the frank disease (1880). Pasteur, realizing the implications, went on to develop, with C. Chamberlain and E. Roux, a vaccine against anthrax (1881) in sheep and cattle, and finally tackled the age-old problem of rabies. Having confirmed the neurotropic character of the virus by its presence in brain and nervous tissues, but with no means of seeing, let alone using cultures of, the agent, Pasteur's only alternative was to use infected spinal cords of sacrificed rabbits, attenuated by drying in air-tight glass containers. Pasteur and his co-workers inoculated dogs with carefully graded material, beginning with samples totally inactivated after 14 days' drying, and working backwards through daily doses increasing in virulence until, on day 14, the inoculation contained fully virulent material from a freshly killed, rabid rabbit. By September 1884, they were able to render dogs wholly resistant to experimental rabies. From there to human prophylaxis, the next step was daunting. Pasteur hoped to make definite progress within two years. His ‘trembling hand’ was forced less than a year later. After a couple of false starts with tragic outcomes (the patients, including a 10-year girl, were seen too late), young Joseph Meister, 9 years old, savaged by a rabid dog on his way to school in a small town in Alsace, was brought to see him in July 1885. Pasteur, faced with the small boy in pain from multiple wounds which would almost certainly kill him if left untreated, overcame his scruples, encouraged by medical colleagues. The post-exposure prophylaxis worked, and Joseph survived; so did a shepherd boy from the Jura treated 3 months later. Rabies vaccination had been successfully launched. There were to be problems ahead, stretching well into the twentieth century. Work to perfect the vaccine continues; and there is still no effective therapy for those unfortunate patients bitten and not receiving prophylaxis in time.

Yellow fever

Yellow fever, endemic in West Africa, travelled to the Americas and elsewhere on board trading ships carrying cargoes of slaves from the sixteenth century onwards. During the nineteenth century there were occasional reverse, if short-lived, importations of the disease to European ports in Spain, France and the west of England.

The agent of yellow fever was identified as a filterable virus, transmitted by mosquitoes (Aëdes aegypti in particular), by W. Reed and colleagues, working in Havana for a United States Army Commission, at the beginning of the twentieth century. Yet it was to take more than two decades before controversies about its aetiology and problems regarding understanding of its pathogenesis and culture methods could result in production of a safe and fully effective, attenuated live virus vaccine, developed by Max Theiler and colleagues at the Rockefeller Institute over a period in the 1930s. By then, the disease had taken its toll among researchers of opposing views, among them Adrian Stokes, who definitively confirmed the agent as a virus, in 1927, and Hideyo Noguchi, who had defended his erroneous theory of a spirochaete, Leptospira icteroides, as the agent of yellow fever for a decade, in 1928.

During World War II Theiler's yellow fever vaccine saved countless lives among both troops and civilians. Jungle yellow fever on the other hand, where the virus is part of a monkey–mosquito cycle involving different species of mosquito including Haemagogus, remains a problem which will prevent complete eradication of the disease for the foreseeable future.

Polio

Poliomyelitis may or may not have been present in antiquity; any evidence is largely pictorial or buried in hieroglyphic records and liable to other interpretations. Identifiable epidemics of paralytic polio begin to appear in the nineteenth century; and work with a bearing on prophylaxis, even after Karl Landsteiner's demonstration of filterability of the agent and its transmissibility to monkeys in 1909, had a number of obstacles to overcome before the long overdue successes of the 1950s. One obstacle was the complexity of the family of polioviruses; another the fact that Landsteiner's experimental animal, the rhesus monkey, is highly susceptible to infection with poliovirus, but only via the respiratory system. The latter fact appeared to support Simon Flexner of the Rockefeller Institute in his rigidly held and influential views, which totally ignored Swedish results, by Carl Kling and others, showing the presence of poliovirus in the intestinal wall and intestinal contents of victims of a severe outbreak in 1911. The work of J. F. Enders, T. H. Weller and F. C. Robbins, who in 1949 were able to grow the virus in cultures of human non-nervous embryonic tissues, finally opened the way to successful production of vaccines against polio. Between 1950 and 1960 three types of vaccine were produced: Jonas Salk used a chemically (formalin) killed vaccine; Albert Sabin and Hilary Koprowsky worked independently on live attenuated virus vaccines. Vast clinical trials were undertaken in the United States in the 1950s. There were disturbing incidents and disasters along the way, but from 1962 onwards, Sabin-type oral vaccines have been successfully used in the United States as well as in Britain and on the European continent.

Emerging viruses

The lastest challenge to virologists is the ‘emerging viruses’. Their story began in Marburg, Germany, in 1967 when 31 laboratory workers using African monkeys as a source of cells for tissue culture material were struck down by an acute infection. Seven died before the cause of the illness was identified as a hitherto unknown virus, carried by the monkeys, which are not affected by it. It became known as Marburg virus. Two years later, in 1969, Lassa fever was first observed in West Africa, when a nurse in a small mission hospital in Lassa, Nigeria, came down with a rapidly developing acute illness with alarming manifestations, from which she died two weeks later. A fellow nurse who had cared for her died in similar circumstances; a third nurse who had cared for both patients also caught the disease, but eventually recovered. The carrier of Lassa fever virus in these cases has been identified as the African rodent Mastomys natalensis, the multimammate mouse.

A third African virus has become notorious since first observed in human infections in Zaire in 1976: Ebola. Again, the clinical picture is alarming, as is the fatality rate. In spite of the virus being identified in electron micrographs within 6 months of the initial outbreak, its natural reservoir and path of transmission to humans remain so far unknown. In 1989 there was a, fortunately rapidly contained, outbreak in the USA, when four human subjects caught the infection from monkeys imported from the Philippines. There was no further spread, and no fatalities; but the threat is still very much present in Africa, in Democratic Republic of the Congo (formerly Zaire) and Gabon, and on the Ivory Coast.

There are indications in early Chinese texts that Hantaviruses as causes of haemorrhagic fevers may have been present there during the first millennium ad. They reappeared as threats to both Eastern and Western societies in the mid-twentieth century as the cause of an outbreak of haemorrhagic fever in 2000 UN troops during the Korean War, preceded by minor ones in Japan, Russia, Scandinavia, and elsewhere on the European continent. Named after the Hantaan river in Korea, the Hantaviruses are carried by rodent vectors and their respective ectoparasites; in the USA by the deermouse and the cottontail rat. Like Lassa fever virus and Ebola and other RNA viruses, the Hantaviruses mutate frequently and use a wide range of hosts; consequently the emergence of new virulent types is an ever present possibility. Their history is open-ended.

HIV and AIDS

The human immunodeficiency virus – HIV, causing AIDS – was first observed in the USA in four homosexual men in 1981. The disease has since caused havoc, both in the Western world and in developing countries, where resurgence of tuberculosis is linked to its prevalence. The virus and the disease have been intensively studied by virologists and public health officials for the last two decades of the twentieth century. Its identification has even caused a latter-day priority dispute involving Luc Montagnier of the Paris Institut Pasteur and Robert Gallo, then at the National Institutes of Health and now at the University of Maryland in Baltimore, USA. In spite of much inspired work by virologists and other medical scientists on both sides of the Atlantic since 1981, and considerable progress made, there are still no long-term therapies or vaccines available in the fight against HIV and AIDS. If and when they are perfected, there will still remain enormous problems of financing and distribution before they can be effectively dispensed throughout developing countries, where prevention and control, and even containment, remain a long way off in an uncertain future, for cultural as well as scientific reasons.

Influenza

In contrast to HIV and AIDS, the influenzas and their viruses have been with humankind for long periods of time. The problem here is that influenza – ‘flu’ – viruses change continually; and although they were shown to be ‘filterable’, and at the same time infectious for both humans and ferrets in the Wellcome/MRC Mill Hill laboratories in the early 1930s, there can be no let-up in work to keep vaccine production abreast of the steady emergence of new types of influenza viruses. Ferrets initially presented a ready-made animal model for vaccine work, but the virus was gradually adapted to growth in the more convenient white laboratory mouse, and later in embryonated eggs and tissue culture. Influenza viruses are subject to antigenic drift and genetic recombination, as well as changes in host specificity (swine flu, avian (wild aquatic birds, and also domesticated ones) flu, etc.). Vaccines are effective, but must consequently be under constant review.

From ‘slow viruses’ to spongiform encephalopathies

The rickettsiae were long ago shown to contain both DNA and RNA and be susceptible to the action of antibiotics, and hence better classified as small bacteria rather than true viruses. The spongiform encephalopathies present far more complex problems in this respect. In 1954 Björn Sigurdsson (1913–1959), outstanding Icelandic virologist and founder, with Rockefeller support, of Reykjavik's Institute for Experimental Pathology, published a classic paper on the sheep disease scrapie. He pointed out striking similarities between scrapie, known in European countries for more than 2 centuries, and a sheep disease called ‘rida’ in Iceland. It had been shown to be transmissible by injection of filtered material from the brain and spinal cord of affected animals by French researchers in 1936. Twenty-five years later J. T. Stamp in Edinburgh would confirm and extend the French results and draw attention to the unusual resistance of the unknown agent and the surprising length of the incubation period. Sigurdsson had introduced the term ‘slow virus infections’; after Gajdusek's work on kuru and CJD (Creutzfeldt–Jakob disease) in the 1950s and 1960s they are now classed as spongiform encephalopathies. The recent furore in Britain over BSE (bovine spongiform encephalopathy) and its possible ability to cross species barriers and cause CJD, and new variant CJD, in humans, has renewed interest in Stanley Prusiner's work on the prion protein and the question of whether or not prions are the sole agents of these diseases, or whether an additional, possibly genetic, factor is involved in the pathogenesis of the spongiform encephalopathies. The identity of prions as small protein molecules with no nucleic acid component would distinguish them from all known viruses, viroids, and infectious agents in general.

Conclusion

It will be clear from the above that isolating and researching emerging viruses, not to mention spongiform encephalopathies, and their epidemiologies, their carriers and possibilities for therapies and control, will keep generations of virologists occupied well into the future. At the same time, international organizations, the WHO in particular, hope to follow up the success with smallpox eradication by ridding the world of similar threats from other virus diseases. First among those on the WHO list at the moment are polio and measles.

Further Reading

  •     CairnsJ, StentGS and WatsonJD (eds) (1966) Phage and the Origins of Molecular Biology. New York: Cold Spring Harbor Laboratory of Quantitative Biology.
  •     FennerF and GibbsA (eds) (1988) Portraits of Viruses. A History of Virology. Basel: Karger.
  •     Grafe A (1991) A History of Experimental Virology, Reckendorf E (transl.) Berlin: Springer-Verlag.
  •     MorseSS (ed.) (1998) Emerging Viruses. Oxford: Oxford University Press.
  •     Oldstone MB (1998) Viruses, Plagues and History. Oxford: Oxford University Press.
  •     Waterson AP and Wilkinson L (1978) An Introduction to the History of Virology. Cambridge: Cambridge University Press.
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