The growth of virus research 1928--1978.

IT WOULD be impossible in a short essay to cover the whole ground of research on viruses, including those infecting vertebrates, insects, plants, bacteria and other organisms. Attention will accordingly be devoted particularly to those aspects of virology of nterest in medicine. (This is the more appropriate as this symposium has been organized in honour of Sir Charles Stuart-Harris, who has so assiduously and profitably cultivated the borderland between clinical medicine and virology.) In the early days of virology, the first task was to determine which infections were definitely caused by viruses. Fifty years ago they were called the filterpassing viruses or just filter-passers. A number of infections had failed to give evidence of bacterial origin and were presumed to be caused by viruses. That this was so was made certain when it was possible to filter the agent through a filter which would hold back bacteria. To do this, however, one needed a test object, perhaps a volunteer in the case of relatively minor infections, preferably an experimental animal. Fifty years ago the viral origin of a few human infections, smallpox and vaccinia, herpes simplex, rabies, measles, dengue and poliomyelitis seemed fairly certain on this basis; and it was suspected that viruses caused mumps, rubella, varicella and influenza. There were also, of course, viruses known to infect domestic animals and plants, to say nothing of bacteriophage. Today the viruses known to infect vertebrates alone number several hundreds. Progressively, the infections in the 'suspected' virus class have been yielding up their mysteries, until very few remain. In almost every instance in the early days, successful transmission was rapidly followed by demonstration of filterability. Important achievements were the transmission to one animal or another of influenza (Smith, Andrewes and Laidlaw, 1933), rubella (Habel, 1941), and St Louis encephalitis (Webster and Fite, 1933). This last was particularly important as it was the forerunner of the isolation of a whole host of arthropod-borne viruses, most of them infecting other species and only incidentally transmitted to man. It is of some interest that before about 1933 the rabbit was the animal of choice for workers in virology; after that the doubtful honour passed decisively to the mouse.