Abstract
BackgroundRecent global reports on malaria suggest significant decrease in disease severity and an increase in control interventions in many malaria endemic countries, including Ghana. However, a major driving force sustaining malaria transmission in recent times is the asymptomatic carriage of malaria parasites, which can enhance immune responses against parasite antigens. This study determined the prevalence and relative avidities of naturally induced antibodies to EBA175RIII–VLl in asymptomatic children living in two communities with varying malaria transmission patterns.MethodsAn asexual stage Plasmodium falciparum antigen, EBA175RIII–VLl was expressed in Lactococcus lactis, purified and used in indirect ELISA to measure total and cytophilic IgG concentrations and avidities in children aged between 6 and 12 years. The children were selected from Obom and Abura, communities with perennial and seasonal malaria transmission, respectively. Venous blood samples were collected in July and October 2015 and again in January 2016. The multiplicity of infection and the genetic diversity of EBA175RIII circulating in both sites were also assessed using polymerase chain reaction.ResultsAsymptomatic parasite carriage in the children from Obom decreased from July (peak season), through October and January, however parasite carriage in children from Abura was bimodal, with the lowest prevalence estimated in October. Antibody concentrations over the course of the study remained stable within each study site however, children living in Obom had significantly higher EBA175RIII–VLl antibody concentrations than children living in Abura (P < 0.05, Mann–Whitney test). Over the course of the study, the relative antibody avidities of EBA175RIII–VLl IgG antibodies were similar within and between the sites.ConclusionNaturally acquired IgG concentrations but not relative antibody avidities to EBA175RIII–V were significantly higher in Obom where malaria transmission is perennial than in Abura, where malaria transmission is seasonal.
Highlights
Recent global reports on malaria suggest significant decrease in disease severity and an increase in control interventions in many malaria endemic countries, including Ghana
The erythrocyte binding antigen 175 (EBA 175, Pf3D7_0731500) is a P. falciparum merozoite ligand that is implicated in erythrocyte invasion, as it is used by the parasite to bind to erythrocytes through interactions with the sialic acid residues of glycophorin A on the erythrocyte during merozoite invasion [11, 12]
The geometric mean P. falciparum parasite density (PD) reduced in moving from July through October to January season in both sites, with PD in July being significantly different from PD in both October and January in both Obom (P < 0.05, Dunn’s Multiple Comparison Test) and Abura (P < 0.001, Dunn’s Multiple Comparison Test)
Summary
Recent global reports on malaria suggest significant decrease in disease severity and an increase in control interventions in many malaria endemic countries, including Ghana. A major driving force sustaining malaria transmission in recent times is the asymptomatic carriage of malaria parasites, which can enhance immune responses against parasite antigens. Acquired antibody responses against recombinant RII have been suggested to inhibit the merozoite binding to glycophorin A, inhibit invasion in vitro and provide protection against clinical malaria [11, 12, 16,17,18,19,20]. EBA175RIII–V has been expressed in E. coli [11, 17, 21] and naturally-induced antibodies against the RIII–V region [20, 21] have been suggested to offer protection against disease in some studies [17, 22]. A recent report suggests that antibodies against RIII–V offer similar levels of protection as a 200fold excess of antibodies against RII [25], suggesting antibodies against RIII–V are more potent than antibodies against RII
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