Plasmodium falciparum: Membrane feeding assays and competition ELISAs for the measurement of transmission reduction in sera from Cameroon

The effect of natural malaria transmission-blocking factors in the blood of Plasmodium falciparum gametocyte carriers was assessed in two types of fun ctional bioassays. In the direct membrane feeding assay (DMFA), a compariso n is made between the infectivity of gametocytes from a naturally infected gametocyte carrier in the presence of autologous plasma and the infectivity in the presence of replacement plasma from nonimmune donors. In the standa rd membrane feeder assay (SMFA), cultured NF54 gametocytes are used to meas ure the capacity of endemic sera to block transmission. In the DMFA, 18 out of 48 sera (37.5%) from Cameroonian gametocyte carriers reduced transmissi on significantly, while in the SMFA 22 out of 48 sera (45.8%) produced tran smission reduction. There was a positive correlation between both assays (r = 0.41, P < 0.05). Antibodies against epitopes of transmission-blocking ta rget antigens Pfs48/45 and Pfs230 were measured in competition ELISAs and c ompared with the results of DMFA and SMFA. Serological reactivity in compet ition ELISAs against three epitopes of Pfs48/45 was significantly higher in the group of transmission-reducing sera in both the DMFA and the SMFA, esp ecially for epitope III. No significant difference was found for Pfs230 ant ibodies (epitope I). Sensitivity of the serological assays was approximatel y 60%, with a specificity of around 70%. Serological tests cannot replace t he functional bioassay in field situations as yet, but can contribute in th e selection of sera for SMFA evaluation. (C) 1999 Academic Press.