The development of the virus concept as reflected in corpora of studies on individual pathogens. 5. Smallpox and the evolution of ideas on acute (viral) infections

IN 1806, Thomas Jefferson was in his second term of office as the third President of the United States.From his neo-classical mansion of Monticello in Virginia, Jefferson wrote on 14 May a letter to Edward Jenner, congratulating him on his discovery of vaccination which Jefferson helped to promote in the United States.After comparing Jenner's discovery favourably with William Harvey's discovery of the circulation of the blood, Jefferson continued in somewhat purple prose: "You have erased from the calendar of human afflictions one of its greatest.Yours is the comfortable reflection that mankind can never forget that you have lived; future nations will know by history only that the loathsome small-pox has existed, and by you has been extir- pated ... .".I The optimism voiced by Jefferson proved to be highly premature.In the last decade, the vast resources of the World Health Organization have been brought to bear on the problem of world-wide eradication of variola; even so, the last pockets of infection have proved more persistent than expected, and optimistic estimates far more recent than Jefferson's remain so far unfulfilled.2On the other hand, in the absence of an animal carrier of the virus of smallpox, complete eradica- tion may be obtained with the help of vaccination, while bubonic plague, carried by a number of rodents, remains endemic over large areas of the globe, including North America.Thus twentieth-century public health authorities still face some degree of challenge from the two major scourges of mankind, which through massive epidemic outbreaks exercised natural population control throughout medieval and early modem history.