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Anthropogenic impacts on Aedes mosquito community dynamics in Côte d'Ivoire

Zahouli, Julien Bi Zahouli. Anthropogenic impacts on Aedes mosquito community dynamics in Côte d'Ivoire. 2017, Doctoral Thesis, University of Basel, Faculty of Science.

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Official URL: http://edoc.unibas.ch/diss/DissB_12471

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Abstract

Background: The recent emergence, re-emergence and spread of arboviral diseases (e.g. yellow fever, dengue, chikungunya and Zika) that are transmitted by Aedes mosquitoes have raised concerns worldwide, and especially in tropical and subtropical regions of the world. In the past several years, Côte d’Ivoire has experienced sporadic, single and dual outbreaks of yellow fever and dengue in the southeastern part of the country, partially explained by high rates of urbanization and intensified agriculture. However, the impacts of these anthropogenic changes (urbanization and transformation of rainforests to vast agricultural areas) on the ecology of Aedes arbovirus vectors remain unexplored. Understanding of the impacts of these anthropogenic factors on the ecology of Aedes mosquitoes is crucial for predicting and preventing arboviral outbreaks, and developing, optimizing and evaluating existing and novel vector control measures and tools aimed at reducing disease incidence.
Objectives: This PhD thesis aimed to assess the anthropogenic impacts, including effects of urbanization and agricultural land use changes, on Aedes mosquito community dynamics in yellow fever and dengue foci in southeastern Côte d’Ivoire. The thesis specifically sought to: (i) explore the oviposition ecology of Aedes mosquitoes and Aedes aegypti dynamics in variously urbanized settings; (ii) assess the larval ecology of Aedes alongside a rural-to-urban gradient; and (iii) evaluate the ecology of Aedes mosquitoes along an anthropogenic disturbance gradient in oil palm-dominated landscapes.
Research partnerships: This PhD thesis was carried out within the frame of an existing and productive partnership between the Swiss Tropical and Public Health Institute (Swiss TPH) and the University of Basel, Basel, Switzerland, the Centre Suisse de Recherches Scientifiques en Côte d’Ivoire (CSRS) and the Université Félix Houphouët-Boigny (UFHB), Abidjan, Côte d’Ivoire and the Liverpool School of Tropical Medicine (LSTM), Liverpool, United Kingdom. The work was funded by Swiss TPH, CSRS and a Scholarship for Foreign Students program (FCS), Bern, Switzerland.
Methods: Aedes mosquito eggs, larvae, pupae and adults were collected along a gradient of urbanization (rural, suburban and urban) and different agricultural land uses, including an oil palm-dominated landscape (rainforest, polyculture, oil palm monoculture and rural housing area). Ovitraps were employed, alongside larval surveys and human-baited double-net trap methods from January 2013 to December 2014. Aedes immatures were reared in the laboratory until adult stage emerged for subsequent species identification. Socio-ecological data were conjointly sampled.
Results: Aedes mosquito ecology significantly varied from rural-to-urban areas and among human-disturbed ecosystems in oil palm-dominated landscapes. A total of 51,439 specimens of Aedes mosquitoes belonging to 20 species (Ae. aegypti, Ae. africanus, Ae. albopictus, Ae. angustus, Ae. apicoargenteus, Ae. argenteopunctatus, Ae. dendrophilus, Ae. fraseri, Ae. furcifer, Ae. haworthi, Ae. lilii, Ae. longipalpis, Ae. luteocephalus, Ae. metallicus, Ae. opok, Ae. palpalis, Ae. stokesi, Ae. unilineatus, Ae. usambara and Ae. vittatus) in rural, suburban and urban areas. The highest Aedes species richness (18 species) was observed in rural areas. A considerably lower Aedes species richness was noted in suburban (seven species) and urban areas (three species). Conversely, the highest Aedes abundance was found in urban (n = 26,072 specimens), followed by suburban (n = 16,787 specimens) and rural (n = 8,580 specimens). Ae. aegypti was the predominant species in all three types of study areas, with the highest abundance in urban areas (n = 26,072; 99.4%).
Aedes mosquito breeding site positivity rate was higher in urban (2,136/3,374; 63.3%), followed by suburban (1,428/3,069; 46.5%) and rural (738/2,423; 30.5%) areas. Rural areas exhibited a larger array of Aedes breeding sites ranging from natural containers (tree holes, coconuts, etc.) to traditional containers (clay pots, calabashes, etc.), and industrial containers (cans, tires, etc.) that hosted several wild species. In contrast, the highest proportions of artificial breeding sites (cans, tires, vehicle bodies, building tools and water storage containers) were found in urban areas where human activities (water storage practices, tire selling and environment management) were favourable to the creation of the breeding sites and proliferation of Aedes mosquitoes, mainly Ae. aegypti. The predatory larvae of Eretmapodites, Toxorhynchites and Culex tigripes were frequently found associated with the larvae of Aedes mosquitoes in rural areas. In all areas, the diversity and proportion of Aedes breeding sites, specimens and species were higher in the peridomestic zones and during the rainy seasons.
Aedes mosquito diversity and distribution were strongly associated with agricultural land-use changes. For example, no Aedes were found in oil palm monocultures. Conversely, the highest Aedes species richness (11 species) was observed in the rainforests, while the highest Aedes abundance (n = 28,276; 60.9%) was found in the polycultures. Aedes females displayed higher anthropophagy tendency in the polycultures (21.5 females/person/day) and the rural housing areas (4.5 females/person/day), and poor anthropophagy (0.6 females/person/day) in the rainforest. Aedes females’ host-seeking activities showed bimodal feeding cycles, with interruption from 11:00 to 14:00 hours in the rural housing areas, and a continuous pattern in the polycultures.
Conclusions: The findings revealed that anthropogenic changes influence significantly the ecology of Aedes mosquitoes by shaping the breeding sites, and altering the species diversity and abundance towards a predominance of Ae. aegypti in urban areas, lack of species in oil palm monocultures, high prevalence of species in polycultures and restriction of wild species in rural areas and rainforests that may serve as bridge vectors. Such Aedes species segregation thus suggests a coexistence of several arbovirus transmission cycles: enzootic, epizootic and epidemic. Moreover, the identification of new Aedes species in rural and forested areas supports the existence of still unidentified enzootic sylvatic transmission cycles of arboviruses. The high abundance of natural breeding sites (e.g. tree holes) of Aedes mosquitoes in the rainforests and rural areas can strongly limit the effectiveness of the removals of discarded containers, and calls for integrated vector management strategies. The evidence generated by this PhD work provides an important contribution to the comprehension of the emergence of arboviral diseases (yellow fever and dengue), Aedes vector surveillance and control in the contexts of urbanization and transformation of rainforests into large industrial oil palm monocultures.
Advisors:Utzinger, Jürg and Koella, Jacob C.
Faculties and Departments:09 Associated Institutions > Swiss Tropical and Public Health Institute (Swiss TPH) > Department of Epidemiology and Public Health (EPH) > Eco System Health Sciences > Health Impact Assessment (Utzinger)
UniBasel Contributors:Utzinger, Jürg
Item Type:Thesis
Thesis Subtype:Doctoral Thesis
Thesis no:12471
Thesis status:Complete
Bibsysno:Link to catalogue
Number of Pages:1 Online-Ressource (xix, 152 Seiten)
Language:English
Identification Number:
Last Modified:22 Apr 2018 04:32
Deposited On:05 Mar 2018 13:01

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