Exploring the heterogeneity of human exposure to malaria vectors in an urban setting, Bouaké, Côte d'Ivoire, using an immuno-epidemiological biomarker

Abstract

Background: In some African cities, urban malaria is a threat to the health and welfare of city dwellers. To improve the control of the disease, it is critical to identify neighbourhoods where the risk of malaria transmission is the highest. This study aims to evaluate the heterogeneity of malaria transmission risk in one city (Bouaké) in a West African country (Côte d'Ivoire) that presents several levels of urbanization.

Methods: Two cross-sectional studies were conducted in three neighbourhoods (Dar-es-Salam, Kennedy and N'gattakro) in Bouaké during both the rainy and dry seasons. Data on insecticide-treated net (ITN) use and blood samples were collected from children aged between 6 months and 15 years to determine the parasite density and the prevalence of Plasmodium falciparum and the level of IgG against the Anopheles gSG6-P1 salivary peptide, used as the biomarker of Anopheles bite exposure.

Results: The specific IgG levels to the gSG6-P1 salivary peptide in the rainy season were significantly higher compared to the dry season in all neighbourhoods studied (all p < 0.001). Interestingly, these specific IgG levels did not differ between neighbourhoods during the rainy season, whereas significant differences in IgG level were observed in the dry season (p = 0.034). ITN use could be a major factor of variation in the specific IgG level. Nevertheless, no difference in specific IgG levels to the gSG6-P1 salivary peptide was observed between children who declared "always" versus "never" sleeping under an ITN in each neighbourhood. In addition, the prevalence of P. falciparum in the whole population and immune responders was significantly different between neighbourhoods in each season (p < 0.0001).

Conclusion: This study highlights the high risk of malaria exposure in African urban settings and the high heterogeneity of child exposure to the Anopheles vector between neighbourhoods in the same city. The Anopheles gSG6-P1 salivary peptide could be a suitable biomarker to accurately and quantitatively assess the risk of malaria transmission in urban areas.

Keywords: Anopheles; Transmission risk; Urban malaria, salivary biomarker of exposure.

Fig. 1

Characterization of Bouaké neighbourhood environment. This figure shows maps of different bio-ecological aspects of Bouaké neighbourhoods (a N’gattakro; b Kennedy; c Dar-es-salam), which could be potential breeding sites of Anopheles. People have transformed shallows to grow rice and vegetable crops and use well water for their field activities

Fig. 2

Comparison of IgG level with gSG6-P1 salivary peptide between neighbourhoods. Dot plots show the individual specific IgG level (∆OD value) to gSG6-P1 in the children of the neighbourhoods studied between the seasons: in the rainy season (n = 281; a) and the dry season (n = 161; b) for the whole “immune responders and not responders to the peptide gSG6-P1” population and for the only immune responders to gSG6-P1 (n = 59; c). Bars indicate the median value in each group. The number in parentheses on the figure above the dot plots indicates values above ∆OD = 2.5. The statistical results using the nonparametric Kruskal–Wallis test are indicated between the groups studied