RELATIONSHIPS BETWEEN CIRCULATING S-ANTIGENS, NATURALLY ACQUIRED ANTIBODIES TO PLASMODIUM-FALCIPARUM EXOANTIGENS AND MALARIA ATTACK IN A MESOENDEMIC AREA

A survey involving 77 individuals living in two savannah villages near Bobo Dioulasso (Burkina Faso, West Africa), was performed in June 1987 (before), August September (during) and January 1988 after the seasonal transmission. The clinical longitudinal study during the seasonal period permitted us to define three different groups in terms of both age and occurrence of malaria attack (MA: greater-than-or-equal-to 5000 parasites/mm3 of blood and axillary fever greater-than-or-equal-to 37.8-degrees-C). The presence of circulating stable antigen (S-Ag) and the antibody responses against exoantigens (E-Ag) of Plasmodium falciparum were also evaluated at three observations periods: beginning, during and after the transmission season. The adult group (III) had the highest rates of IgG Ab to E-Ag although, IgM prevalence to E-Ag was maximal in the group II (individuals with no malaria attack and age less-than-or-equal-to 15 years old). Group I (persons with less-than-or-equal-to 15 years old and who contracted at least one MA) did not have any S-Ag at the first observation period and showed the lowest rate of antibodies to E-Ag. The probability of occurrence of an MA calculated from these parameters at the beginning of the transmission period were correct in 78.9% of the cases in children (Groups I & II) and in 71.8% of adults during the subsequent transmission period. Therefore these values could be used for evaluating the probability of occurrence of a clinical MA during the transmission period in a mesoendemic area. S-Ag and antibodies to E-Ag could participate positively in the mechanisms involved in the development of the immune status.