Abstract
BackgroundAsymptomatic carriage of Plasmodium falciparum is widespread in adults and children living in malaria-endemic countries. This study identified the prevalence of malaria parasites and the corresponding levels of naturally acquired anti-parasite antibody levels in afebrile adults living in two communities in the Greater Accra Region of Ghana.MethodsTwo cross-sectional studies conducted in January and February 2016 and repeated in July and August 2016 recruited subjects aged between 6 and 75 years from high parasite prevalence (Obom) and low parasite prevalence (Asutsuare) communities. Whole blood (5 ml) was collected from each volunteer, plasma was aliquoted and frozen until needed. An aliquot (10 µl) of the blood was used to prepare thick and thin blood smears, 100 µl was preserved in Trizol and the rest was separated into plasma and blood cells and each stored at − 20 °C until needed. Anti-MSP3 and Pfs230 antibody levels were measured using ELISA.ResultsAsexual parasite and gametocyte prevalence were higher in Obom than Asutsuare. Antibody (IgG, IgG1, IgG3, IgM) responses against the asexual parasite antigen MSP3 and gametocyte antigen Pfs230 were higher in Obom during the course of the study except for IgM responses against Pfs230, which was higher in Asutsuare than in Obom during the rainy season. Antibody responses in Asutsuare were more significantly associated with age than the responses measured in Obom.ConclusionThe pattern of antibody responses measured in people living in the high and low malaria transmission setting was similar. All antibody responses measured against the asexual antigen MSP3 increased, however, IgG and IgG1 responses against gametocyte antigen Pfs230 decreased in moving from the dry to the peak season in both sites. Whilst asexual and gametocyte prevalence was similar between the seasons in the low transmission setting, in the high transmission setting asexual parasite prevalence increased but gametocyte prevalence decreased in the rainy season relative to the dry season.
Highlights
Asymptomatic carriage of Plasmodium falciparum is widespread in adults and children living in malaria-endemic countries
The results showed that in the dry season, the independent variables could not explain the variations observed in total Immunoglobulin G (IgG) responses in Obom and could only account for 3.3% of the variations in total IgG observed in Asutsuare (Table 2)
Afebrile adults and children were recruited from communities of varying malaria transmission intensities and parasite prevalence to enable the comparison of naturally acquired immune responses against asexual and sexual stage antigens in both the dry and subsequent rainy season
Summary
Asymptomatic carriage of Plasmodium falciparum is widespread in adults and children living in malaria-endemic countries. Antibodies against Pfs230 have been detected in populations naturally exposed to malaria parasites [14, 15] Such antibodies together with specific antibodies generated in small rodents have been shown to inhibit parasite development in the standard membrane-feeding assay (SMFA) considered the ‘gold standard’ assay for functional transmission-blocking antibodies [16,17,18]. These antibodies, have been suggested to be very short lived, peaking during the transmission season [19] and are more prevalent in children than in adults [15]
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