Urbanisation is a main driver for Aedes aegypti dynamics and arboviral risk in Côte d’Ivoire

Abstract

Abstract Background Aedes mosquito-borne arboviruses have (re-)emerged and caused considerable public health concerns in major sub-Saharan African cities subjected to rapid urbanisation. We assessed the effects of urbanisation on Aedes aegypti dynamics and biting pattern, and the risk of transmission of yellow fever (YF) and dengue (DEN) viruses along urban-rural gradient in Côte d'Ivoire. Methods We collected Aedes mosquitoes as eggs, larvae/pupae, and adults seasonally in urban, suburban and rural areas using ovitrap, larval survey and human-baited double net trap methods from January 2015 to December 2016. We sampled household data and characterised Aedes larval breeding sites. Ae. aegypti indices and biting rates were compared by area. Results Ae. aegypti was the most abundant species in all areas. It showed higher abundance in urban areas (n = 26,072; 99.4%). Larval indices were associated with human activities, including waste and water management. Tires and discarded containers were the most productive breeding sites in all areas. Household water receptacles displayed high Aedes-positive rate (23.6%) in urban areas. Positive ovitrap index was higher in urban (53.5%) compared to suburban (43.1%) and rural (29.7%). Stegomyia indices were highest in urban followed by suburban and rural areas, with respective house index of 67.2, 51.4 and 27.8, container index of 57.1, 43.5 and 19.7, and Breteau index of 95.2, 78.9 and 8.8. Biting rate was 4.3 and 2.7-fold higher in urban (83.5 bite/person/day) and suburban (52.1 bite/person/day) compared to rural (19.4 bite/person/day), respectively. Ae. aegypti indices were higher during rainy seasons. Conclusions In Côte d'Ivoire, urbanisation raised Ae. aegypti abundance and biting rate. As a result, YF and DEN risk indices were above WHO-established epidemic thresholds in urban area thus exposing local communities to high risk of getting diseases. Integrated community-based vector control programs should be applied to reduce arboviral risk. Key messages Urbanisation raises Aedes aegypti abundance and arboviral disease risk in Côte d’Ivoire. Integrated community clean-up actions are required to control Aedes vectors.