Search

The health district of Sakassou is one of the 83 health districts in Côte d'Ivoire, located in a zone with very high malarial transmission rates, with an incidence rate of ≥40% Therefore, to guide vector control methods more effectively, it was crucial to have a good understanding of the vectors in the area. This study aimed to determine the level of malarial transmission during the dry season in Sakassou, Côte d'Ivoire. Female Anopheles mosquitoes were sampled using human landing catches (HLCs) and pyrethrum spraying catches (PSCs). The larvae were collected using the ‘dipping’ method. A total of 10,875 adult female mosquitoes of Anopheles gambiae were collected. The PCR analysis revealed that all individuals were Anopheles coluzzii. The geographical distribution of potential breeding sites of Anopheles showed the presence of An. coluzzii in all the wetlands of the city of Sakassou. During the dry season, the human-biting rate of An. coluzzii was 139.1 bites/person/night. An exophagic trend was displayed by an adult female of An. coluzzii. The entomological inoculation rate during the dry season was 1.49 infectious bites/person/night. This study demonstrated that An. coluzzii was the main vector of malarial transmission in Sakassou, and the intensity of transmission remains high throughout the dry season. HIGHLIGHTS Effect of rice-growing regions on malarial transmission during the dry season in Sakassou was studied.; Provide novel insights into the dynamics of transmission during this period.; Areas used for irrigation of rice are potential breeding sites of Anopheles coluzzii.; This geographical focus provides valuable information for targeted vector control interventions in specific areas.; Offering critical information for malaria control programs.;

Abstract Background Several studies were carried out in experimental hut station in areas surrounding the city of Bouaké, after the crisis in Côte d’Ivoire. They reported increasing resistance levels to insecticide for malaria transmiting mosquitoes. The present work aims to evaluate the current resistance level of An. gambiae ( s.l.) in rural and urban areas in the city of Bouaké. Methods Larvae of Anopheles gambiae (s.l.) were collected from five different study sites and reared to adult stages. The resistance status was assessed using the WHO bioassay test kits for adult mosquitoes, with eight insecticides belonging to pyrethroids, organochlorines, carbamates and organophosphates classes. Molecular assays were performed to identify the molecular forms of An. gambiae (s.l.), the L1014F kdr and the ace-1R alleles in individual mosquitoes. The synergist PBO was used to investigate the role of enzymes in resistance. Biochemical assays were performed to detect potential increased activities in mixed function oxidase (MFO) levels, non-specific esterases (NSE) and glutathione S-transferases (GST). Results High resistance levels to pyrethroids, organochlorines, and carbamates were observed in Anopheles gambiae (s.l.) from Bouaké. Mortalities ranged between 0 and 73% for the eight tested insecticides. The pre-exposure to PBO restored full or partial susceptibility to pyrethroids in the different sites. The same trend was observed with the carbamates in five sites, but to a lesser extent. With DDT, pre-exposure to PBO did not increase the mortality rate of An. gambiae (s.l.) from the same sites. Tolerance to organophosphates was observed. An increased activity of NSE and higher level of MFO were found compared to the Kisumu susceptible reference strain. Two molecular forms, S form [(An. gambiae (s.s)] and M form (An. coluzzi) were identified. The kdr allele frequencies vary from 85.9 to 99.8% for An. gambiae (s.s.) and from 81.7 to 99.6% for An. coluzzii. The ace-1R frequencies vary between 25.6 and 38.8% for An. gambiae (s.s.) and from 28.6 to 36.7% for An. coluzzii. Conclusion Resistance to insecticides is widespread within both An. gambiae (s.s.) and An. coluzzii. Two mechanisms of resistance, i.e. metabolic and target-site mutation seemed to largely explain the high resistance level of mosquitoes in Bouaké. Pyrethroid resistance was found exclusively due to the metabolic mechanism.

Malaria is a parasitic vector disease whose transmission is linked to a combination of multiple factors related to the vector, the parasite, the human host and its environment. In addition to the high prevalence in the tropical zone, the endemic malaria area, there are significant disparities in the transmission of the disease between rural and urban areas, where the highest prevalence of malaria is observed, but also within the cities themselves. While the city, which appears to be unfavourable to the vector and should therefore contribute to reducing malaria transmission, can be observed to maintain it. However, the transmission is uneven because of certain intrinsic characteristics of the city described as heterogeneous, dense and open. In Bouaké, the second largest city in the Ivory Coast after Abidjan, several years of military-political crisis have resulted in emptying some neighborhoods where the bush has regained ground, increasing the density where populations have remained, disrupting the health care system and weakening the economic power of the city dwellers. Using a geographical approach, our study aimed to measure the risk of malaria transmission in urban sub-spaces illustrating the changes undergone by the city during the crisis and to identify the factors that make it possible to explain the spatial disparities in the distribution of malaria. A geographical survey identified Kennedy and Dar-Es-Salam 1 as urban sub-spaces. An update of land use was conducted using field surveys and Google Earth to establish a geographical database for use in the analysis of sociological, parasitological and entomological data which were collected during several field surveys. The land use update showed that only 50.5% of the developed lots were inhabited in Kennedy, compared with 91.5% in Dar-Es-Salam 1. Parasitological data showed that the prevalence of malaria was significantly higher at Kennedy (33.5%) compared to Dar-Es-Salam 1 (10.2%) (p = 0.0001). Similarly, the aggressiveness of vector mosquitoes (Anopheles gambiae s.l.) was higher in Kennedy (20.6 p / h / n) than in Dar-Es-Salam 1 (1.2 p / h / n) (p = 0.0001). Sociological surveys revealed a different use of prevention tools by neighborhood, but rates of possession of long-lasting treated mosquito nets and ways of seeking care were similar. Results showed significant spatial disparities in the transmission of malaria in the two neighborhoods studied, while the practices of prevention and health care do not really differ.