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National audience; Les méthodes de surveillance entomologique mises en œuvre par les services de santé (ex. cartographie des gites larvaires d’Ae. albopictus, piégeage des moustiques femelles adultes…) ont des limites importantes, en particulier quant à leur déploiement à grande échelle et leur fiabilité. Pour mesurer l’exposition humaine aux piqûres d’Aedes albopictus, la mise au point d’un nouvel outil sérologique qui s'appuierait sur la détection dans le sang humain d'anticorps, pourrait être utilisé sur le terrain par les opérateurs publics de démoustication et serait d’intérêt pour la santé publique. Ainsi, l’objectif principal du projet "Exp-Albo" consistait à identifier et à valider un biomarqueur d’exposition aux piqûres d’Ae. albopictus.

International audience

Background In malaria-endemic areas, human populations are frequently exposed to immunomodulatory salivary components injected during mosquito blood feeding. The consequences on pathogen-specific immune responses are not well known. This study evaluated and compared the humoral responses specific to merozoite stage vaccine candidates of Plasmodium falciparum, in children differentially exposed to Anopheles bites in a natural setting. Methods The cross-sectional study was carried out in Bouake (Cote d'Ivoire) where entomological data and blood samples from children (0-14 years) were collected in two sites with similar malaria prevalence. Antibody (IgG, IgG1, IgG3) responses to PfAMA1 and PfMSP1 were evaluated by ELISA. Univariate and multivariate analysis were performed to assess the relationship between the immune responses to P. falciparum antigens and exposure to Anopheles bites in the total cohort and in each site, separately. The individual level of exposure to Anopheles bites was evaluated by quantifying specific IgG response to the Anopheles gSG6-P1 salivary peptide, which represents a proxy of Anopheles exposure. Results The anti-Plasmodium humoral responses were different according to the level of exposure of children, with those highly exposed to Anopheles presenting significantly lower antibody responses to PfMSP1 in total population (IgG and IgG3) and in Petessou village (IgG, IgG1, IgG3). No significant difference was seen for PfAMA1 antigen between children differently exposed to Anopheles. In Dar-es-Salam, a neighbourhood where a high Culex density was reported, children presented very low antibody levels specific to both antigens, and no difference according to the exposure to Anopheles bites was found. Conclusion These findings may suggest that immunomodulatory components of Anopheles saliva, in addition to other factors, may participate to the modulation of the humoral response specific to Plasmodium merozoite stage antigens. This epidemiological observation may form a starting point for additional work to decipher the role of mosquito saliva on the modulation of the anti-Plasmodium acquired immunity and clinical protection in combining both field and ex vivo immunological studies.

Studies done in Bouake (Cote d'Ivoire) about 20-yr ago reported that Anopheles gambiae s.l. Giles was the major malaria vector. The present study aimed to update these data and to identify the main vectors. Mosquitoes were collected in Allokokro and Petessou villages between June 2014 and December 2015 using the human landing catching method. Potential breeding sites of An. gambiae s.l. were identified in August and October 2014 and mapped using GPS. Anopheles species were morphologically and molecularly [polymerase chain reaction (PCR)] identified. Ovaries of female were dissected to determine the parity and infection with Plasmodium was detected in head and thorax by quantitative PCR. In Allokokro, the biting rate of An. gambiae s.s was significantly greater than Anopheles coluzzii, whereas, in Petessou, biting rates of both species were comparable. Plasmodium falciparum (Haemosporida: Plasmodiidae), Plasmodium malariae (Haemosporida: Plasmodiidae), and Plasmodium ovale (Haemosporida: Plasmodiidae) identified in both villages.The infection rates of An. gambiae s.s. and An. coluzzii were not significantly different. The entomological inoculation rate (EIR) of An. gambiae s.s. for P. falciparum was 9-fold greater than that of An. coluzzii in Allokokro; however, in Petessou, the EIRs of both species were comparable. In both village, An. gambiae s.s was responsible for P. falciparum and P. ovale transmission whereas An. coluzzii transmitted all three Plasmodium species.

International audience; Environmental changes related to agricultural practices and activities can impact malaria transmission. In the objective to evaluate this impact on the human-vector contact, the level of human exposure to Anopheles vector bites was assess by an immuno-epidemiological indicator based on the assessment of the human IgG antibody response to the Anopheles gambiae gSG6-P1 salivary peptide, previously validated as a pertinent biomarker. Two cross-sectional surveys were carried out in the dry and rainy season in three villages with intensive agricultural plantations (N'Zikro with rubber cultivation, Ehania-V5 and Ehania-V1 with palm oil exploitation) and in a control village without plantations (Ayébo). Overall, 775 blood samples were collected in filter papers from children aged 1 to 14 years-old for immu-nological analysis by ELISA. The IgG levels to the gSG6-P1 salivary peptide significantly differed between studied villages both in the dry and the rainy seasons (P b 0.0001) and were higher in agricultural villages compared to the control area. In particular, the level of specific IgG in Ehania-V5, located in the heart of palm oil plantations, was higher compared to other agricultural villages. Interestingly, the level of specific IgG levels classically increased between the dry and the rainy season in the control village (P b 0.0001) whereas it remained high in the dry season as observed in the rainy season in agricultural villages. The present study indicated that rubber and oil palm plantations could maintain a high level of human exposure to Anopheles bites during both the dry and rainy seasons. These agricultural activities could therefore represent a permanent factor of malaria transmission risk.

Additional file 2. IgG level with gSG6-P1 salivary peptide according to the use of insecticide-treated nets (ITN) in the whole population (A) and in age groups (B and C). Fig. A: IgG level to gSG6-P1 peptide in the whole population according to the ITN use in the rainy (Fig. A1) and dry (Fig. 1B) seasons. Fig. B: IgG level to gSG6-P1 peptide in “under 5 years” age group according to the ITN use in the rainy (Fig. A1) and dry (Fig. 1B) seasons. Fig. C: IgG level to gSG6-P1 peptide in “over 5 years” age group according to the ITN use in the rainy (Fig. A1) and dry (Fig. 1B) seasons.

BackgroundIn 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 (Bouake) in a West African country (Cote d'Ivoire) that presents several levels of urbanization.MethodsTwo cross-sectional studies were conducted in three neighbourhoods (Dar-es-Salam, Kennedy and N'gattakro) in Bouake during both the rainy and dry seasons. Data on insecticide-treated net (ITN) use and blood samples were collected from children aged between 6months and 15years 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.ResultsThe 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

Urban malaria is an underestimated serious health concern in African countries. This study aimed to evaluate the risk of malaria transmission in an urban area by evaluating the level of human exposure to Anopheles bites using an Anopheles salivary biomarker (gambiae Salivary Gland Protein-6 peptide 1 [gSG6-P1] peptide). Two multidisciplinary cross-sectional studies were undertaken in five sites of Bouake city (three urban districts and two surrounding villages, used as control; Cote d'Ivoire) during the rainy season and the dry season. Blood samples were obtained from children 6 months to 14 years of age for immunological tests. The level of anti-gSG6-P1 immunoglobulin G (IgG) antibodies was significantly higher in the rainy season than the dry season in both urban and rural sites (P < 0.0001). Interestingly, children with the highest anti-gSG6-P1 IgG responses in the rainy season were infected by Plasmodium falciparum. Surprisingly, no difference of anti-gSG6-P1 IgG level was observed between urban and rural areas, for either season. The current data suggest that children in the urban city of Bouake ' could be as highly exposed to Anopheles bites as children living in surrounding villages. The immunological biomarker of human exposure to Anopheles bites may be used to accurately assess the potential risk of malaria transmission in African urban settings.

Arbovirus infections, mainly transmitted by Aedes mosquito, are emerging in Africa. Efficient vector control requires an understanding of ecological factors which could impact on the risk of transmission, such as environmental changes linked to agricultural practices. The present study aims to assess the level of human exposure to Aedes mosquito bites in different agroecosystem area, using an immunological tool which quantifies human IgG antibody response to one Ae. aegypti salivary peptide. Specific IgG responses were assessed during dry and rainy seasons, in children living in different villages in Cote d'Ivoire: N'Zikro (rubber and oil palm exploitations), Ehania-V5 (oil palm), and Ayebo (without intensive agricultural activities). In the dry season, specific IgG levels were significantly lower in Ayebo compared to Ehania-V5 and N'Zikro and, interestingly, were similarly high in both villages with cultivations. In the rainy season, no difference of specific IgG was observed between villages. Specific IgG responses remained therefore high during both seasons in villages associated with intensive agricultural. The rubber and oil palm cultivations could maintain a high level of human exposure to Aedes mosquito bites during both dry and rainy seasons. These agricultural activities could represent a permanent risk factor of the transmission of arboviruses.

L’expansion rapide et l’implantation durable du moustique tigre (Aedes albopictus) en France métropolitaine et dans les territoires d'outre‐mer font craindre le déclenchement de foyers épidémiques d’arboviroses telles la dengue, le chikungunya et la fièvre Zika. En l’absence de traitements ou de vaccins efficaces, la lutte antivectorielle (LAV) est la seule méthode envisageable pour contrôler ce risque et diminuer les densités de moustiques du genre Aedes. Toutefois, les méthodes de surveillance entomologique mises en oeuvre par les services de santé ont des limites importantes, en particulier quant à leur déploiement à grande échelle et leur fiabilité. Comment évaluer avec précision l’exposition. Pour mesurer l’exposition humaine aux piqûres d’Aedes albopictus, la mise au point d’un nouvel outil sérologique pourrait représenter, sur le terrain, une alternative intéressante aux méthodes entomologiques actuelles.

L'expansion rapide et l'implantation durable du moustique tigre (Aedes albopictus) en France métropolitaine et dans les territoires d'outre-mer font craindre le déclenchement de foyers épidémiques d'arboviroses telles la dengue, le chikungunya et la fièvre Zika. En l'absence de traitements ou de vaccins efficaces, la lutte anti-vectorielle (LAV) est la seule méthode envisageable pour contrôler ce risque et diminuer les densités de moustiques du genre Aedes