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An epidemiological risk indicator based on purely entomological factors can be used to identify regions which are at higher risk of transmission within the endemic forest zones of Ivory Coast, and can serve to point out biotopes to be treated to make antivector campaigns more effective. In the forests of Ivory Coast, so-called socially open environments which are populated by a great number of ethnic groups who are highly mobile and whose amps are spread over a large area, are particularly vulnerable to epidemics of the disease. Transmission always occurs near water: at rivers, water holes, plantations. By contrast, socially closed societies consisting of a single ethnic group settled in a village are at much lower risk. It seems that human behaviour plays as much a role in transmission dynamics as environmental changes which may be more or less favourable to the vector.

The extraction of rough antigens (Ag) from trypanosomes came across a major problem getting of a high number of parasites. Moreover several technics for the extraction of rough antigens are described. Some of them are sophisticated and time consuming. Aiming the obtention of a large number of Ag for this study, inoculation of trypanosomes into Cricetomys gambianus and affinity chromatography of blood allow to collect of large number of trypanosomes. This new technique leads to the extraction of 50 to 60 mg of rough Ag of trypanosomes isolated from infected Cricetomys. In order to set up a specific and sensitive serological diagnosis of gambian human trypanosomiasis, the different rough Ag were used comparatively by ELISA and Latex Agglutination tests. Confirming previous works, the results indicate a high sensitivity and a doubtful specificity for both techniques.

Methods for mass preparation of crude antigen and exoantigen of Trypanosoma gambiense from experimentally infected Cricetomys gambianus are described. The size of this animal and the hyperparasitism obtained make it a remarkable source of trypanosomian antigens.

A comparative study, by ELISA, of purified exoantigen and of five crude antigenic extracts from several strains of T.b. gambiense and T.b. brucei has shown a wide range of results. The best sensitivity is obtained with virulent strains from human origin. For more accuracy, an association of such antigens would be preferable.