The ecology and control of cutaneous Leishmaniasis vectors in the sub-Andean mountainous zone of Huila department, Colombia

Abstract

This thesis describes a series of studies designed to improve our understanding of the transmission cycle of cutaneous leishmaniasis (CL) in the coffee-growing sub-Andean region of Huila department and to explore the use of insecticide treated bednets as an alternative control measure to the current policy of house spraying. The thesis is divided into six chapters, including four results chapters. Chapter 1 reviews the public health importance of CL in the Andean region, in Colombia and in Huila department; explores the possible risk of CL in coffee plantations at regional, departmental and municipal levels; and presents a brief summary on control strategies in the Andes, Colombia and Huila. Chapter 2 describes an exploratory study in seven representative areas within the sub-Andean region (1000 - 2000 m a.s.l. ) of Huila department designed to identify possible CL vectors and the ecological determinants for their distribution and abundance. The study helps to: (i) explain the current distribution of CL in Huila department; (ii) identify the boundaries of the epidemic area; and (iii) identify new areas of potential risk for the disease which should be considered for monitoring or prevention programs. The main findings were: (1) the CL foci of Huila was identified geographically; (2) Lutzomyia longiflocosa appears to be the principal sandfly vector, having a narrow ecological niche defined largely by altitude, temperature and a preference for a well structured forest or forest-like habitat (i. e. traditional coffee- growing area); (3) there was no evidence for complete adaptation of L. longiflocosa to intensive coffee plantations; and (4) L. nuneztovari is a generalist species which has at most a limited secondary vectorial role in this region. Chapter 3 describes a cross-sectional study at household level in three villages (267 houses) designed to (i) identify environmental risk factors for the suspected vectors and (ii) identify demographic, environmental and entomological risk factors for disease. The main findings were: (1) stronger evidence incriminating L. longiflocosa as the main vector, and confirming the less important role of L. nuneztovari, (2) the detected risks confirmed the feasibility of the use of insecticide treated bednets (ITNs) as a control measure for CL. Chapter 4 describes a series of field studies to evaluate the use of lamdacyhalothrin treated bed nets as an alternative control measure (to house spraying) for CL within the study area: (1) the entomological efficacy of ITNs was tested under controlled conditions; (2) the entomological effectiveness (measured indirectly by indoor CDC light traps) of ITNs and house spraying were both measured in a V household-based intervention trial; (3) the reliability of light traps as an indicator of indoor sandfly exposure (in the previous study) was tested by comparison with indoor human landing catches; and (4) field bioassays were used to measure the residual lethal effect of the insecticide up to 4 months after both interventions were implemented in the effectiveness trial. Together, the efficacy and effectiveness studies showed that ITNs reduce L. longiJlocosa indoor human landing rates, blood feeding success, and Human Blood Index. The effects of house spraying were unclear, as the reduction in sandfly numbers (fed and unfeds) observed in light traps in sprayed houses was not reflected by any reduction in human landing catches. Chapter 5 describes a questionnaire study of the inhabitants in the epidemic area to evaluate their knowledge, attitudes and practices in relation to sandfly and CL control in Huila. The study showed that (i) bednets were widely used, but less so amongst the poorest households, and (ii) nets were commonly used to reduce sandfly nuisance rather than reduce the risk of CL. However knowledge of sandfly involvement in CL transmission was positively associated with net usage. This information should help inform the design of future ITN campaigns in the region. Finally, Chapter 6 summarises and integrates the main findings of the four results chapters, recommends the provision of ITNs to replace house spraying for CL control in Huila, and proposes future studies which should be prioritised.