Abstract
BackgroundAssessment exposure and immunity to malaria is an important step in the fight against the disease. Increased malaria infection in non-immune travellers under anti-malarial chemoprophylaxis, as well as the implementation of malaria elimination programmes in endemic countries, raises new issues that pertain to these processes. Notably, monitoring malaria immunity has become more difficult in individuals showing low antibody (Ab) responses or taking medications against the Plasmodium falciparum blood stages. Commonly available techniques in malaria seroepidemiology have limited sensitivity, both against pre-erythrocytic, as against blood stages of the parasite. Thus, the aim of this study was to develop a sensitive tool to assess the exposure to malaria or to bites from the vector Anopheles gambiae, despite anti-malarial prophylactic treatment.MethodsAb responses to 13 pre-erythrocytic P. falciparum-specific peptides derived from the proteins Lsa1, Lsa3, Glurp, Salsa, Trap, Starp, CSP and Pf11.1, and to 2 peptides specific for the Anopheles gambiae saliva protein gSG6 were tested. In this study, 253 individuals from three Senegalese areas with different transmission intensities and 124 European travellers exposed to malaria during a short period of time were included.ResultsThe multiplex assay was optimized for most but not all of the antigens. It was rapid, reproducible and required a small volume of serum. Proportions of Ab-positive individuals, Ab levels and the mean number of antigens (Ags) recognized by each individual increased significantly with increases in the level of malaria exposure.ConclusionThe multiplex assay developed here provides a useful tool to evaluate immune responses to multiple Ags in large populations, even when only small amounts of serum are available, or Ab titres are low, as in case of travellers. Finally, the relationship of Ab responses with malaria endemicity levels provides a way to monitor exposure in differentially exposed autochthonous individuals from various endemicity areas, as well as in travellers who are not immune, thus indirectly assessing the parasite transmission and malaria risk in the new eradication era.
Highlights
Assessment exposure and immunity to malaria is an important step in the fight against the disease
In this study, a multiplex assay to simultaneously measure responses to 13 peptides derived from pre-erythrocytic P. falciparum Ags and 2 peptides derived from one A. gambiae salivary Ag has been developed
In agreement with previous data, the present results showed that for some of these peptides, such as Lsa1-41, Lsa1J, Lsa3NR2, Glutamate-rich protein (Glurp), Salsa2, StarpR, circumsporozoite protein (CSP) and SR11.1, the proportion of seropositive individuals clearly increases with malaria exposure levels (Figure 3), and higher Ab response rates were seen with the Lsa1-41, Glurp, Salsa2, and CSP peptides
Summary
Assessment exposure and immunity to malaria is an important step in the fight against the disease. The aim of this study was to develop a sensitive tool to assess the exposure to malaria or to bites from the vector Anopheles gambiae, despite anti-malarial prophylactic treatment. Some indicators that help in monitoring these factors are the incidence of clinical malaria cases and the estimation of the exposure to vector bites. Such methods for monitoring malaria impact can be time-consuming, subjective and impractical. The Ab immune response against Plasmodium Ags can be used as one means to evaluate the exposure to malaria in travellers, even when they take anti-malarial chemoprophylaxis [8]. Evaluation of the human response to arthropod salivary antigens could be an epidemiological indicator of exposure to vector bites, as described for the P. falciparum vector A. gambiae [9]
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