[Yellow fever in Western Africa, 1973-1987. Observed facts--studies realized, campaign, prevention and forecast].

This global analysis of the situation is based on a review of notifications, observations and studies concerning yellow fever in 16 of 17 countries of the West African subregion (Algeria is not affected for the years 1973-1987). In view of this analysis and the epidemiological picture, the author proposes a plan of concerted action to confine yellow fever to its monkey-to-monkey cycle in the wild. Official notifications vary greatly from one country to the next. Any of five major causes could explain this: ecological and ethological conditions that favour circulation of the virus in the wild and man-to-man transmission to different extents; the immune status of the populations; the difficulty of diagnosing especially isolated cases; lack of means for investigation; and negligence. The quantity and gravity of human cases are systematically underestimated, sometimes to a great extent. Lack of resources and difficulty of diagnosis, but also in many instances the attitude of the population, can account for this. Modern means of investigation, faster intervention by specialists, and better knowledge of how the virus is transmitted, have shown recently an increasing gap between notifications and the actual situation. Research and monitoring programmes are particularly important. The programmes under way in Senegal and Côte d'Ivoire have already resulted in considerable improvement in the action against epidemics. Because of these programmes, our knowledge of the very complex pattern of viral circulation is improving, thereby helping us develop systems for prevention and enabling us to forecast epidemics. Priority areas for study and research are: (i) Basic programmes for detailed study of all the topotypes of the virus, and identification of the viral amplification cycles that recur over several years. Such studies are under way in Senegal and Côte d'Ivoire. They would be particularly useful in Ghana and in Nigeria, where the taxonomy and bioecology of A. africanus s.l. should also be studied. (ii) Surveys of sylvatic vectors should show, for the endemic zones of each country, the type of contact between sylvatic vectors and man in both rural and wild biotopes. (iii) A complete map of the Stegomyia foci with an assessment of their potential epidemic risk (an analysis of the productivity of the sites depending on their type). (iv) Assessment of the immune status of the populations of the various ecosystems of each country, taking account of past or present vaccination strategies. There are several prevention strategies to choose from. The author advocates preparation of a scientifically based, subregional plan for optimum cost effectiveness.(ABSTRACT TRUNCATED AT 400 WORDS)