Malaria seroepidemiology: comparison between indirect fluorescent antibody test and enzyme immunoassay using bloodspot eluates

Blood sampling on filter paper is a current practice in malaria seroepidemiological studies by indirect fluorescent antibody test (IFAT). There is, however, scant comparative information about the use of bloodspot eluates for detection of malarial IgG antibodies simultaneously by IFAT and enzyme immunoassay (ELISA). Here we report data obtained by both serological methods done on 219 bloodspot eluate samples collected in a rural community in Brazilian Amazon Basin (Alto Paraiso, Ariquemes municipality) where malaria is endemic. Plasmodium falciparum and P. vivax thick smear antigens were used in the IFAT; a detergent-soluble P. falciparum antigen was prepared for ELISA. Substantial agreement of results (Kappa coefficient k = 0.686) was observed when P. falciparum antigen was used in both tests, and IFAT titers were found to be strongly correlated to ELISA antibody units (Spearman correlation coefficient rs = 0.818, p < 0.001). Only moderate agreement (k = 0.467) between IFAT with P. vivax antigen and ELISA with P. falciparum antigen was observed. Spearman correlation coefficient value between quantitative results (IFAT titers and ELISA antibody units) in this case was numerically lower (rs = 0.540, p < 0.0001). Our results suggest that, with P. falciparum antigen, both IFAT and ELISA performed on bloodspot eluates are equivalent for seroepidemiological purposes.