Population dynamics in rural areas freed from Onchocerciasis in West Africa : Benin (CEFORP), Burkina Faso (UERD), Cote D'ivoire (ENSEA), Ghana (Rips), Guinea (DNSI), Mali (DNSI), Niger (DSCN), Senegal (DPS), Togo (URD) : synthesis of national monographs - Quesnel, André (CICRED, 1999)