Patterns of Aedes aegypti immature ecology and arboviral epidemic risks in peri-urban and intra-urban villages of Cocody-Bingerville, Cote d'Ivoire: insights from a dengue outbreak

Abstract

BackgroundIn Cote dIvoire, Aedes vector studies and arboviral outbreak responses have mostly focused on urbanized neighborhoods including intra-urban villages, but have often neglected peripheral villages. We assessed and compared Aedes aegypti population dynamics and dengue (DEN) and yellow fever (YF) epidemic risks among peri-urban and intra-urban villages during the 2023-2024 DEN outbreaks in Cocody-Bingerville, southern Cote dIvoire. MethodsFrom August 2023 to July 2024, we sampled Aedes eggs, larvae and pupae in the domestic and peridomestic ecozones of three peri-urban and three intra-urban villages. We compared Ae. aegypti larval infestation, container productivity, Stegomyia indices (house index: HI, container index: CI, and Breteau index: BI) and pupal indices (pupae per house index: PHI, pupae per container index: PCI, and pupae per person index: PPI) between the study villages. ResultsAedes aegypti widely dominated Aedes fauna in both peri-urban (98.1%) and intra-urban (99.8%) villages. Immatures were sampled from seven container types. However, the most productive containers were small containers, tires and medium containers which produced 81.8% of all the pupae in the peri-urban villages, and tires and small containers yielding 83.2% in the intra-urban villages. These key containers produced substantially more pupae in the domestic ecozones (70.9%) in the peri-urban villages, but equitably between the domestic (48.8%) and peridomestic (51.2%) ecozones in the intra-urban villages. In each study village, they yielded around 90% and 80% of pupae during the short dry and long rainy seasons, respectively. CI, HI and BI were comparable between the peri-urban (29.9%, 35.9% and 41.4) and intra-urban (36.7%, 48.0% and 56.2) villages, and surpassed the World Health Organization (WHO) DEN and YF epidemic thresholds. PCI (1.26 vs. 3.38 pupae/container) and PHI (1.75 vs. 5.18 pupae/house) were lower in the peri-urban than in the intra-urban villages, while PPI (0.54 vs. 1.25 pupae/person) was similar between the villages. Unlike temperature and relative humidity, all indices were strongly associated with rainfall in all the study villages. ConclusionIn Cocody-Bingerville, all sampled peri-urban and intra-urban villages exhibited high densities of Ae. aegypti immatures and habitats. Although larval habitats were diverse, a limited number of container types accounted for over 80% of pupal production. Stegomyia indices remained consistently elevated, exceeding WHO epidemic thresholds for DEN and YF across all study villages, potentially contributing to ongoing DEN outbreaks. Therefore, vector surveillance and outbreak responses should be extended to peri-urban villages, as they could act as arbovirus re-introduction sources. Community-based interventions targeting the identified key containers could help control the outbreaks. This study provides a baseline for strategically reducing human exposure to arboviruses in the study villages.