Abstract
Background: Plasmodium falciparum malaria remains a major public health concern globally though there is some decline due to scale-up of control efforts. Evaluation of the anti-malarial immune profile, in populations residing in epidemic-prone areas in the dry season or at the time when vector control largely reduced man-mosquito contact, would help predict malaria burden when future epidemics occur. Methods: A cross-sectional study was designed to investigate antibody responses to four P. falciparum blood stage vaccine candidate antigens in non-febrile individuals from Shewa Robit in north-central Ethiopia where malaria transmission was expected at a minimal level as a result of the sampling season and effective vector control. Blood samples were analyzed microscopically for Plasmodium detection. The enzyme-linked immunosorbent assay (ELISA) was used to measure immunoglobulin (IgG) antibodies to apical membrane antigen 1 (AMA1), glutamaterich protein (GLURP) R2 region and merozoite surface protein 2 (MSP2) allelic variants. Results: Study participants were smear-negative for Plasmodium infection. While 51 (22%) of the participants reported that they had never been exposed to clinical malaria in life, 177 (78%) reported at least one clinical malaria episode with laboratory confirmed P. falciparum infection. The antigens tested were well-recognized by the test sera although significant differences were observed in antibody prevalence and level between the different antigens and there was inter-individual variability. IgG response to the antigens showed age-related pattern but without evidence of relation with status and frequency of reported past exposure to clinical malaria. Conclusion: The data suggests that individuals in an epidemic-prone malaria setting have reactive and stable antibodies that readily recognize P. falciparum blood-stage vaccine candidate antigens in the absence of slidepositivity. Analysis of age-related pattern in antibody level showed positive association with age but unrelated with increasing frequency of reported episode suggesting the role of intrinsic age-related factors in malaria immune maturation.
Highlights
Plasmodium falciparum malaria remains a major public health concern globally though there is some decline due to scale-up of control efforts
Plasmodium falciparum malaria is among the leading causes of morbidity and mortality worldwide [1]
(22%) of the study participants reported that they had not been exposed to any clinical malaria in life time in spite of residing in endemic area(s) (Table 1)
Summary
Plasmodium falciparum malaria remains a major public health concern globally though there is some decline due to scale-up of control efforts. Though it has been difficult to look into the effect of age on malaria immunity independent of exposure, these investigators argued that they managed to do so. There was no significant difference in malaria antibody levels between individuals more extensively exposed and those with less exposure [5]. Another unresolved issue in malaria immunity is that antibody responses decline rapidly with time in the absence of persistent boost infections [6]. There are evidences contrary to this assertion
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