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

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

Évaluation de la composition spécifique des glossines, vectrices de la Trypanosomose Humaine Africaine, dans la région de Ndendé au sud du Gabon

Objectifs: Afin d’évaluer la composition spécifique des glossines dans les biotopes savanicoles et forestiers, une étude entomologique a été réalisée sur ces insectes dans la région de Ndendé (province de la Ngounié), ancien foyer de la Trypanosomose Humaine Africaine (THA) pour identifier les sites potentiels de transmission de cette parasitose.Méthodologie et résultats: Un total de 14 pièges vavoua a été utilisé dont 7 pièges placés le long des cours d’eau présents dans la galerie forestière et 7 autres en savane proche des villages, du 23 octobre au 7 novembre 2015. Au total, 697 glossines ont été capturées (DAP=3,32 glossines/piège/jour). La plus forte abondance des glossines a été obtenue en forêt avec 678 spécimens. Cependant, ces glossines ont été faiblement capturées en savane (19 spécimens). Ces glossines se répartissent en quatre espèces dont Glossina fuscipes fuscipes, Glossina frezili, Glossina nashi et Glossina palpalis palpalis. G. fuscipes fuscipes (95%) a été l’espèce la plus abondante alors que G. frezili (1%), G. nashi (2%) et G. palpalis palpalis (2%) ont été très faiblement capturées.Conclusion et application: Cette étude a permis d’identifier dans la région de Ndendé, quatre espèces de glossines qui vivent en sympatrie. Par ailleurs, la forte abondance de G. fuscipes fuscipes et la présence de G. palpalis palpalis, vecteurs de la THA dans les différents biotopes prospectés, avec une forte prédominance enforêt, suggèrent une existence probable d’un risque de transmission des trypanosomes dans la région de Ndendé. Par conséquent, le biotope forestier serait une zone prioritaire pour une lutte antivectorielle afin de limiter les risques de transmission de cette parasitose. Aussi, ces résultats invitent à la réalisation des travaux plus détaillés visant à identifier la dynamique spatio-temporelle des glossines et leur rôle dans la transmission éventuelle de la THA dans la région de Ndendé au sud du Gabon.Mots-clés: Trypanosomose humaine africaine, glossine, composition spécifique, savane, forêt, GabonEnglish AbstractObjectives: In order to assess the species composition of tsetse flies among savannah and forested biotopes, an entomological survey was conducted on these insects in the Ndende region (province of Ngounié), ancient focus of Human African Trypanosomiasis (HAT) for identifying the potential sites of the HAT transmission.Methodology and results: A total of 14 Vavoua traps was used with 7 traps installed along the rivers present in the forest gallery and 7 others in the savannah near the villages. The study was done from 23rd October to 7th November 2015. In total, 697 tsetse flies were captured (ADT=3.32 tsetse flies/trap/day). The highest abundance of tsetse flies was found in the forest with 678 specimens, while the lowest abundance was observed in the savannah with 19 specimens. The identified tsetse flies are G. fuscipes fuscipes, G. nashi, G. frezili and G. palpalis palpalis. G. fuscipes fuscipes (95%) was the most abundant species. Conversely, G. frezili (1%), G. nashi (2%) and G. palpalis palpalis (2%) were less in number.Conclusion and application: The results of this study showed the presence of four tsetse flies species, biological vectors of HAT, in the Ndendé region. The high abundance of G. fuscipes fuscipes and the presence of G. palpalis palpalis, vectors of HAT, in different savannah and forested biotopes, with strong predominance inforest, suggest a probable risk of transmission of trypanosomes in the Ndende region. Thus, the forested biotope would be the priority areas for implementing a vector control in order to limit the risks of HAT transmission. Therefore, these results require studies aiming at identifying spatial and temporal dynamics of tsetse flies and their role in the eventual transmission of HAT in the Ndendé region, southern of Gabon.Keywords: Human African trypanosomiasis, tsetse fly, species composition, savannah, forest, Gabo

Caractérisation des insectes et des champignons infestant les fèves de cacao dans les principales zones de production en Côte d’Ivoire

If the culture of the cocoa in Côte d’Ivoire gives a great satisfaction concerning the production level, the quality of raw cocoa beans remains to be improved. One of the causes of this depreciation is the moulds development in beans. In order to identify responsible fungus, cocoa beens have been collected in the maine production areas which are the East, the Mid-West and the South-West, represented respectively by the localities of Abengourou, Oumé and Soubré. From collected beans, the fungus have been insulated and purified on PDA medium and then, they have been identified by observing their morphocultural and microscopic characteristics. The results show that 9 mushroom species belonging to 5 genera were identified in cocoa beans collected in the whole of the localities. There are Aspergillus, Penicillium, Fusarium, Curvularia and Streptomyces. Among them, the Aspergillus genus which is able to produce ochratoxine, was found with an appearance frequency of 86.30 %

Research agenda for preventing mosquito-transmitted diseases through improving the built environment in sub-Saharan Africa

Mosquito-transmitted diseases are a major threat to health in sub-Saharan Africa, but could be reduced through modifications to the built environment. Here we report findings from a major workshop held to identify the research gaps in this area, namely: (1) evidence of the health benefits to changes to the built environment, (2) understanding how mosquitoes enter buildings, (3) novel methods for reducing mosquito-house entry, (4) sustainable approaches for reducing mosquito habitats, (5) case studies of micro-financing for healthy homes and (6) methods for increasing scale-up. Multidisciplinary research is essential to build out mosquito-transmitted diseases, and not build them in