Human IgG responses to Anopheles gambiae immunogenic salivary proteins in urban and rural populations of Burkina Faso: biomarkers of exposure to malaria vector bites

Abstract

Background: Malaria control would be greatly facilitated by the development of new tools for rapidly assessing malaria transmission intensity. In malaria-endemic areas such as Burkina Faso, human populations are frequently exposed to immunomodulatory salivary components injected during mosquito blood feeding. Numerous studies have examined parasite immunity; however, there are few data available on vector immunity as a means of assessing malaria transmission in sub-Saharan Africa. The present study aims to compare IgG-specific response to salivary gland extracts (SGE) of Anopheles gambiae (An. gambiae) in populations living in urban and rural areas in Burkina Faso. Methods: A cross-sectional descriptive study was carried out in two sites, Ouagadougou city and Sapouy village, where blood samples (n = 676) from children (0–15 years) and adults were collected. After An. gambiae salivary protein isolation, the antibody (IgG) response to those SGE was evaluated by enzyme-linked immunosorbent assay (ELISA), representing a proxy of Anopheles exposure. The difference in antibody concentrations between groups was tested using parametric tests (Student’s t-test and analysis of variance [ANOVA]) and the nonparametric Mann–Whitney U (Wilcoxon rank-sum) test. All differences were considered significant at P < 0.05. Results: The study population consisted of 63.0% males and 37.0% females (average age = 31.2 ± 17.8 years). IgG antibodies against An. gambiae salivary protein were detected in all study participants. Urban participants demonstrated a greater mean IgG level to An. gambiae bites than rural (P < 0.0001). The mean IgG level was higher in secondary school children compared with primary school children (P < 0.0001). Organic cotton farmers held higher IgG to An. gambiae bites than conventional cotton farmers (P = 0.0027). Conclusions: The evaluation of IgG specific to mosquito salivary gland extracts as immunological biomarkers in populations in Burkina Faso allowed us to show that the human anti-SGE IgG level to An. gambiae bites is strongly influenced by the living environment and the use of insecticides in agriculture.