Abstract
BackgroundAdvances in malaria control have reduced the burden of disease resulting from exposure to parasite infections. The consequences on naturally acquired immunity are unclear. A magnetic bead-based immunoassay (MBA) to assess antibody levels in populations living in endemic areas was previously evaluated. In this study, the effect of clinical attacks on immunity was analysed in three sentinel sites of Ivory Coast.MethodsRecombinant proteins or peptides derived from liver or blood stage antigens of Plasmodiumfalciparum (CSP, LSA141, LSA3, SALSA, PF13-DBL1α1, GLURP, AMA1, MSP1p19, MSP4p20), the CSP of Plasmodium malariae and the salivary glands antigen of Anopheles gambiae (gSG6) were covalently linked to a colour-coded microsphere (Luminex™ beads) for the multiplex assay. ELISA was used for whole parasite extract antigen. Blood samples (n = 94) of patients consulting for symptomatic malaria attacks and living in three different malaria endemic settings (rural and periurban) were analysed.ResultsHighly variable seroprevalence of antibody responses against parasite antigens was found ranging from 3 (gSG6) to 97 % (MSP4p20). A marked prevalence and significantly higher level of antibodies was found in patients from the rural site (Korhogo), those harbouring the lowest level of parasitaemia. The use of whole schizont extract could not discriminate immunity level, contrary to parasite-derived recombinant proteins or peptides. Prevalence of responders to LSA141 and levels of antibodies to PF13 were significantly different between the three settings. Moreover, the post-treatment clearance of parasites was clearly associated with a significantly higher level of antibody response for almost 50 % of the parasite antigens tested.ConclusionThe multiplex MBA-Magpix technology assay provides an accurate high throughput monitoring of parasite-specific antibodies during symptomatic malaria. The levels of antibody responses may provide a risk criterion with respect to the degree of parasitic infection. Additionally, they can be used as an indicator in the implementation of malaria prevention and local control strategies.
Highlights
Advances in malaria control have reduced the burden of disease resulting from exposure to parasite infections
It has been established that areas of unstable, low, malaria transmission such Gambia and Kenya are characterized by a persistent risk of clinical malaria in older children and adults whereas in areas with stable, high-level of malaria transmission the risk of clinical malaria decreases markedly after the age of 5 years [2, 3]
Different profile and levels of antibody responses from malaria symptomatic patients according to different transmission settings were evidenced. These results indicate that the antibody response to antigens derived from Plasmodium falciparum, Plasmodium malariae or Anopheles gambiae can be used as relevant biomarkers to evaluate follow-up and prevention measures at community level
Summary
Advances in malaria control have reduced the burden of disease resulting from exposure to parasite infections. The effect of clinical attacks on immunity was analysed in three sentinel sites of Ivory Coast. The large-scale deployment of combined interventions strategies, including insecticide impregnated bed nets, rapid diagnostic tests and efficient combination therapy, led to a decrease of malaria burden in several sub-Saharan African areas [4]. Several tools are useful for follow-up progress of controls and decrease of malaria burden. For estimating the risk of malaria transmission or infection, the entomological inoculation rate (EIR) is considered as a gold standard. With the decreasing transmission rate resulting from enlarged control programmes and scarcity of positive mosquitoes makes this method labour-intensive
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