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The concept of nation-wide or even global eradication of malaria originated from the findings that 1) interruption of transmission of the four species of plasmodia infecting man throughout large areas was possible with indoor residual spraying with DDT, and 2) malaria parasites usually disappear spontaneously from infected persons in less than 3 years, permanently interrupting transmission. From this standpoint three types of malaria may be considered: 1) responsive, when the vectors die after alighting on a sprayed surface for sufficient time, carrying with them malaria parasites that may be within their bodies, thereby interrupting transmission; 2) refractory, when due to a natural or acquired behavior of the mosquitoes, or to resistance to the insecticide, some of the vectors may survive the application of the insecticide; and 3) inaccessible, when due to cultural patterns or to the state of mind of the affected populations it is not possible to spray dwellings. Only responsive malaria is now eradicable; fortunately it is extensive, and current successes prefigure further benefits. Eradication of refractory malaria must be deferred, with few exceptions, but the disease can be reduced by adequate application of residual insecticides. Inaccessible malaria must await profound changes in cultural patterns or states of mind, but fortunately the affected populations are small and frequently isolated, and the required changes may not be far away.
Therefore, eradication of malaria must at present be considered unstable, regional, and temporary. Until malaria disappears from the world there are risks of losing what has been accomplished in a given country. That more than one-third of the population of former malarious areas lives in zones where the disease has been eradicated, and that another third inhabits regions under eradication programs, constitute a great achievement. Slow progress, however, in the rest of the world indicates that further efforts should be made, particularly in financing the relevant programs in the developing countries. It is also of great importance to delimit the areas where malaria, because of being refractory or inaccessible, will not be soon eradicated. Changes in strategy are necessary—general public-health activities in hyperendemic areas are not effective in the presence of malaria; the funds they use might be better designated for efficient indoor residual spraying. On the other hand, simple control programs should be regarded with more enthusiasm in countries that are at present unable to undertake eradication, as the insecticide represents the best method to improve health in the highly endemic areas.
As the maintenance phase will be long-lasting, it is essential that the work performed be simple and of low cost. I advise that the malaria-eradication service be transformed, after the objective is achieved, into a vector-borne-diseases control service, which would maintain eradication while producing benefits in other fields.
* Read at the Inter-Congressional Plenary Session No. 6 on "Progress and Prospects of Global Malaria Eradication," Eighth International Congresses on Tropical Medicine and Malaria, Teheran, Iran, 10 September 1968.
At present on leave of absence as Professor, Simón Bolivar Chair of Latin American Studies, University of Cambridge, Department of Human Ecology Building, Gresham Road, Cambridge CB1 2ES, England.
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