The abolition of infection: hope or illusion?

David Tyrrell's Rock Carling lecture covers a wider range of topics than its title suggests 1. The emergence of new organisms and new infectious diseases, the possible contribution of infectious agents to the aetiology of diseases of unknown cause, antibiotic resistance, immun- ization and genetic engineering are all considered in a personal and orginal way which will be of interest to any- one concerned with the study of infection. One of Tyrrell's dominant concerns is the control of infection. In Europe, changes in social and environ- mental conditions brought about the virtual disappear- ance of infections such as cholera, typhoid and leprosy without the introduction of any specific control pro- grammes. There is little doubt that similar results could be achieved in many parts of the developing world if their populations could be provided with adequate housing, clean water and a good diet. Unfortunately, there is little chance that these goals will be achieved in the near future unless there is a radical change in the attitude of the rich countries of the world towards their poorer neighbours. In such circumstances specific, and relatively inexpensive, control measures such as vaccination are an attractive option to health planners. The dramatic success of the smallpox eradication campaign has shown what can be achieved. Could other infections be abolished in the same way? This question was the theme of a meeting held recently at the National Institutes of Health in the US. At the NIH meeting some of the factors that con- tributed to the success of the smallpox eradication programme were reviewed 2. These included the distinctive clinical features of the infection, the absence of carriers and an animal reservoir, the low infectivity of patients during the incubation period, the availability of a heat-stable vaccine and the fact that successful vaccination produces a visible scar. Other factors which must also have been important are sound leadership, the involvement in the programme from the beginning of a group of able epidemiologists and laboratory scientists and the co-operative efforts of the countries where smallpox occurred. A short-list of further candidates for eradication has been prepared 3. This includes measles, poliomyelitis, yaws, yellow-fever and guinea worm. A strong case can be made for placing guinea worm high on the list * since this disabling and economically important infection can be eradicated by the provision of piped water and by the treatment with insecticide of the stagnant pools in which infected cyclops may be found. An ambitious programme to eradicate guinea worm from India by 1985 is under- way. Poliomyelitis virus is another potential candidate for elimination. Eradication of wild poliovirus has been achieved already in a number of industrialized countries following mass immunization with either killed or live vaccine. Whether such immunization programmes would be equally successful in tropical developing countries where poor standards of hygiene prevail is unknown. Despite the progress of the World Health Organization's Expanded Programme on Immunization (EPI) measles still kills many children in the developing world, perhaps as many as one million a year. In addition, measles frequently precipitates malnutrition and it can leave behind a legacy of blindness and chronic lung disease. For these reasons the discussions that are currently taking place about the possible eradication of measles are exciting:. Eradication of measles will not be easy 6. Measles shares with smallpox some of the characteristics which favoured eradication of the latter such as a characteristic clinical presentation, the'absence of an animal reservoir and the availability of a heat-stable vaccine 7. On the other hand compared with smallpox, measles is more infectious and more difficult in sur- veillance terms; also, measles immunization produces no scar. Despite these drawbacks several industrialized countries have made considerable progress towards the local elimination of measles and the indigenous infection has now been eliminated from 90 % of American statest Elimination of measles from developing countries will be more difficult because in many of them measles occurs in the urban population at an early age when conventional measles vaccines are ineffective because of maternally transmitted antibody. Thus, the recent report by Sabin and his colleagues 8 that seroconversion was successfully induced in 4-6-month-old Mexican infants with an inhaled aerosol vaccine is an exciting development. This finding, if confirmed in more extensive trials, could pro- vide the key to the eradication of measles in the developing world. A mass measles immunization campaign, preferably carried out world-wide over a short period, would be difficult and expensive and beyond the financial and logistic resources of some of the world's poorest countries. Fortunately, there are sound financial reasons why the wealthy countries of the world might be prepared to help. The control programme under way may succeed in eliminating indigenous measles from the United States but, even if this goal is achieved, mass immunization will have to be continued indefinitely as long as the risk of measles importation remains. In the United States measles immunization costs around 10-25 million dollars a year and other industrialized countries must spend a proportionally equivalent sum on their own immuniza- tion programmes. If measles could be abolished world- wide this recurrent expenditure would be saved.