Spatial and temporal variation of malaria entomological parameters at the onset of a hydro-agricultural development in central Côte d'Ivoire

A deeper understanding of the ecology and small-scale heterogeneity of malaria transmission is essential for the design of effective prevention, control and elimination interventions. The spatial and temporal distribution of malaria vectors was investigated in five villages in close proximity to a hydro-agricultural system in Côte d'Ivoire over the course of construction and the early phase of irrigated rice farming.; The study was carried out in five villages (Raffierkro, N'Douakro, Ahougui, Kpokahankro, Koffikro) near Bouaké, central Côte d'Ivoire, between early 2007 and late 2009. In each village, mosquitoes were collected by human landing catches and identified morphologically at genus and species level, and entomological parameters were determined. Plasmodium infection was assessed by dissection and an enzyme-linked immunosorbent assay.; A total of 19,404 mosquitoes belonging to the genus Anopheles were sampled during 328 human-night catches. Before the construction of the hydro-agricultural system, comparable densities of Anopheles gambiae were observed in all villages. In subsequent years, densities in Raffierkro and Ahougui were significantly higher than the other villages [Kruskal-Wallis (KW) test = 31.13, p > 0.001]. The density of Anopheles funestus in the five villages was comparable in the early stage of the project, while a high density was reported in Koffikro at the end (KW test = 11.91, p = 0.018). Transmission of Plasmodium falciparum is perennial in the study area. Over the course of the study, high entomological inoculation rates (EIRs) were found: 219-328 infectious bites per person per year with An. gambiae. For An. funestus considerably lower EIRs were observed (5.7-39.4). Changing patterns of An. gambiae were not correlated with malaria transmission.; In this study setting, located in the bioclimatic transition zone of Côte d'Ivoire, rice cultivation was not observed to increase malaria transmission. The entomological parameters recorded until the onset of rice-growing activities in a hydro-agricultural system presented considerable heterogeneity both in space and time; a strong increase of Anopheles mosquitoes was observed in two of the five villages located in close proximity to the dam and irrigated rice fields. Malaria still is a main public health problem in all villages that require adequate control measures

Efficacy of ICON® Maxx in the laboratory and against insecticide-resistant Anopheles gambiae in central Côte d'Ivoire

ABSTRACT: BACKGROUND: Long-lasting treatment kits, designed to transform untreated nets into long-lasting insecticidal nets (LLINs), may facilitate high coverage with LLINs where non-treated nets are in place. In this study, the efficacy of ICON(R) Maxx (Syngenta) was evaluated under laboratory conditions and in an experimental hut trial in central Cote d'Ivoire, where Anopheles gambiae s.s. are resistant to pyrethroid insecticides. METHODS: In the laboratory, polyester and polyethylene net samples were treated with ICON(R) Maxx, washed up to 20 times and their efficacy determined in World Health Organization (WHO) cone assays against a susceptible laboratory An. gambiae s.s. colony. Over a 12-month period, the polyester nets were evaluated in a hut trial to determine mosquito deterrence, induced exophily, blood-feeding inhibition and mortality. RESULTS: In the laboratory, ICON(R) Maxx-treated polyethylene nets showed higher efficacy against pyrethroid-susceptible mosquitoes than polyester nets. After 20 washings, insecticidal efficacy in bioassays was 59.4% knockdown (KD) and 22.3% mortality for polyethylene, and 55.3% KD and 17.9% mortality for polyester nets. In experimental huts, treated nets showed strong deterrence, induced exophily and an over three-fold reduction in blood-fed mosquitoes. More than half (61.8%) of the mosquitoes entering the huts with treated nets were found dead the next morning despite high levels of KD resistance. After washing the treated nets, KD and mortality rates were close to or exceeded predefined WHO thresholds in cone bioassays. CONCLUSION: In contrast to previous laboratory investigation, ICON(R) Maxx-treated nets showed only moderate KD and mortality rates. However, under semi-field conditions, in an area where mosquitoes are resistant to pyrethroids, ICON(R) Maxx showed high deterrence, induced exophily and provided a significant reduction in blood-feeding rates; features that are likely to have a positive impact in reducing malaria transmission. The WHO cone test may not always be a good proxy for predicting product performance under field condition

Entomological drivers of uneven malaria transmission in urban lowland areas in Bouaké, Côte d’Ivoire

Abstract Background The use of urban lowlands for agriculture contributes to the food security of city- dwellers, but promotes malaria transmission. The objective of the study was to characterize the entomological drivers of malaria transmission in two lowlands (N’Gattakro and Odiennekourani) in the city of Bouaké, Côte d’Ivoire. Methods The human landing catch technique was used to capture mosquitoes in houses located at the edge of two lowlands in Bouaké from February to December 2019. Cultivated surfaces were calculated monthly in both lowlands for each crop type (rice and market gardening) using images acquired by a drone. The different mosquito species were identified morphologically and by PCR analysis for the Anopheles gambiae complex. Anopheles infection by Plasmodium parasites was assessed by quantitative PCR. Mosquito diversity, biting behaviour and rhythmicity, and malaria transmission were determined in each lowland and compared. Results Anopheles gambiae sensu lato (s.l.) was predominant in N’Gattakro and Culex quinquefasciatus in Odiennekourani. Four Anopheles species were identified: An. gambiae s.l. and Anopheles funestus s.l. in both lowlands, Anopheles pharoensis in N’Gattakro, and Anopheles ziemanni in Odiennekourani. Within the An. gambiae complex, three species were caught: An. gambiae sensu stricto (s.s.), Anopheles coluzzii, and Anopheles arabiensis for the first time in Côte d’Ivoire (30.1%, 69.9% and 0% in N’Gattakro, and 45.1%, 52.6% and 2.4% in Odiennekourani, respectively). Anopheles gambiae s.l. species exhibited a significant exophagic behaviour in N’Gattakro (77.1% of outdoor bites versus 52.2% in Odiennekourani). In N’Gattakro, 12.6% of captures occurred before bedtime (09.00 pm) and after waking up (05.00 am), 15.1% in Odiennekourani. The mean human biting rate was higher in N’Gattakro than in Odiennekourani (61.6 versus 15.5 bites per person per night). Overall, Anopheles infection rate was 0.68%, with 0.539 and 0.029 infected bites per person per night in N’Gattakro and Odiennekourani, respectively. Conclusion The risk of malaria in urban agricultural lowland areas is uneven. The role of agricultural developments and irrigation patterns in the production of larval habitat should be explored. The exophagic behaviour of Anopheles vectors raises the question of the residual transmission that needs to be assessed to implement appropriate control strategies

Influence of Host-Related Factors and Exposure to Mosquito Bites on the Dynamics of Antibody Response to Plasmodium falciparum Antigens

Humoral immunity to Plasmodium falciparum is acquired after repeated infections, and can lead to clinical protection. This study aimed to evaluate how human-, parasite-, and environment-related determinants can modulate the dynamics of IgG responses to Plasmodium falciparum after an infection. Individuals (n = 68, average age = 8.2 years) with uncomplicated malaria were treated with ACT and followed up for 42 days. IgG responses to P. falciparum merozoite antigens (PfMSP1, PfMSP3, PfAMA1, PfGLURP-R0), to whole schizont extract (PfSchz), and to Anopheles gSG6-P1 and Aedes Nterm–34 kDa salivary peptides were measured. Regression analyses were used to identify factors that influence the dynamics of IgG response to P. falciparum antigen between D0 and D42, including demographic and biological factors and the level of exposure to mosquito bites. The dynamics of IgG response to P. falciparum differed according to the antigen. According to multivariate analysis, IgG responses to PfSchz and to PfGLURP-R0 appear to be affected by exposure to Aedes saliva and are associated with age, parasite density, and anti-Plasmodium pre-existing immune response at study inclusion. The present work shows that human exposure to Aedes saliva may contribute, in addition to other factors, to the regulation of anti-Plasmodium immune responses during a natural infection