Impact of Community-Based Larviciding on the Prevalence of Malaria Infection in Dar es Salaam, Tanzania.

The use of larval source management is not prioritized by contemporary malaria control programs in sub-Saharan Africa despite historical success. Larviciding, in particular, could be effective in urban areas where transmission is focal and accessibility to Anopheles breeding habitats is generally easier than in rural settings. The objective of this study is to assess the effectiveness of a community-based microbial larviciding intervention to reduce the prevalence of malaria infection in Dar es Salaam, United Republic of Tanzania. Larviciding was implemented in 3 out of 15 targeted wards of Dar es Salaam in 2006 after two years of baseline data collection. This intervention was subsequently scaled up to 9 wards a year later, and to all 15 targeted wards in 2008. Continuous randomized cluster sampling of malaria prevalence and socio-demographic characteristics was carried out during 6 survey rounds (2004-2008), which included both cross-sectional and longitudinal data (N = 64,537). Bayesian random effects logistic regression models were used to quantify the effect of the intervention on malaria prevalence at the individual level. Effect size estimates suggest a significant protective effect of the larviciding intervention. After adjustment for confounders, the odds of individuals living in areas treated with larviciding being infected with malaria were 21% lower (Odds Ratio = 0.79; 95% Credible Intervals: 0.66-0.93) than those who lived in areas not treated. The larviciding intervention was most effective during dry seasons and had synergistic effects with other protective measures such as use of insecticide-treated bed nets and house proofing (i.e., complete ceiling or window screens). A large-scale community-based larviciding intervention significantly reduced the prevalence of malaria infection in urban Dar es Salaam

Community knowledge and acceptance of larviciding for malaria control in a rural district of east-central Tanzania

The use of microbial larvicides, a form of larval source management, is a less commonly used malaria control intervention that nonetheless has significant potential as a component of an integrated vector management strategy. We evaluated community acceptability of larviciding in a rural district in east-central Tanzania using data from 962 household surveys, 12 focus group discussions, and 24 in-depth interviews. Most survey respondents trusted in the safety (73.1%) and efficacy of larviciding, both with regards to mosquito control (92.3%) and to reduce malaria infection risk (91.9%). Probing these perceptions using a Likert scale provides a more detailed picture. Focus group participants and key informants were also receptive to larviciding, but stressed the importance of sensitization before its implementation. Overall, 73.4% of survey respondents expressed a willingness to make a nominal household contribution to a larviciding program, a proportion which decreased as the proposed contribution increased. The lower-bound mean willingness to pay is estimated at 2,934 Tanzanian Shillings (approximately US$1.76) per three month period. We present a multivariate probit regression analysis examining factors associated with willingness to pay. Overall, our findings point to a receptive environment in a rural setting in Tanzania for the use of microbial larvicides in malaria control. © 2014 by the authors; licensee MDPI, Basel, Switzerland

An analytically tractable, age-structured model of the impact of vector control on mosquito-transmitted infections

Vector control is a vital tool utilised by malaria control and elimination programmes worldwide, and as such it is important that we can accurately quantify the expected public health impact of these methods. There are very few previous models that consider vector-control-induced changes in the age-structure of the vector population and the resulting impact on transmission. We analytically derive the steady-state solution of a novel age-structured deterministic compartmental model describing the mosquito feeding cycle, with mosquito age represented discretely by parity—the number of cycles (or successful bloodmeals) completed. Our key model output comprises an explicit, analytically tractable solution that can be used to directly quantify key transmission statistics, such as the effective reproductive ratio under control, Rc, and investigate the age-structured impact of vector control. Application of this model reinforces current knowledge that adult-acting interventions, such as indoor residual spraying of insecticides (IRS) or long-lasting insecticidal nets (LLINs), can be highly effective at reducing transmission, due to the dual effects of repelling and killing mosquitoes. We also demonstrate how larval measures can be implemented in addition to adult-acting measures to reduce Rc and mitigate the impact of waning insecticidal efficacy, as well as how mid-ranges of LLIN coverage are likely to experience the largest effect of reduced net integrity on transmission. We conclude that whilst well-maintained adult-acting vector control measures are substantially more effective than larval-based interventions, incorporating larval control in existing LLIN or IRS programmes could substantially reduce transmission and help mitigate any waning effects of adult-acting measures

A participatory approach for malaria control in southern Malawi : Effects of the environment and community on larval source management

Current trends in the fight against malaria suggest that further progress will be difficult with  the use of insecticide-based control measures alone. Without major reductions in the burden of malaria registered in the past few years, the use of additional interventions with synergistic effects on the current standard measures is required. Currently, interest in employing Larval Source Management (LSM) as a complementary tool is growing as it has shown to significantly reduce larval densities and consequently adult populations in settings where it has been applied along other interventions. LSM is commonly executed via 1) habitat modification, which includes physical transformation of a larval habitat through draining, filling and land levelling and 2) larviciding, commonly using an endotoxin-producing bacterial larvicide, Bacillus thuringiensis var. israelensis (Bti). Knowledge on the ecology of anopheline larval habitats is therefore important as it informs where LSM should be targeted. Also, knowledge about community acceptance and participation in LSM is important as it affects the scalability and future sustainability of the intervention. The study described in this thesis focused on the potential of community-led LSM in Malawi. Chapter 2 describes the habitat ecology of malaria vectors in the Majete area, southern Malawi. In this area, anopheline larvae develop in habitats with little silt, surrounded by bare-grounds and occupied by culicine larvae. I conclude that larval control should be directed towards such anopheline-productive habitats which sustain malaria transmission. In Chapter 3, I investigated whether application of Bti induces discrimination of treated sites by gravid females seeking oviposition sites. I found that treatment of the sites with the bacterial larvicide does not repel ovipositing females from laying eggs in such sites. This finding implies that the female mosquitoes did not detect the presence of the larvicide in aquatic sites. In Chapter 4, we explored whether application of lower doses (sublethal) of Bti in larval habitats can negatively affect fitness parameters of malaria vectors and hence their ability to successfully transmit malaria. Sublethal Bti doses are likely to occur when applications are done under field conditions, especially by local communities who may lack the desired expertise in comparison with trained experts. Immature and adult life history parameters, including larval survival, adult longevity, wing size and oviposition of An. coluzzii, an important African malaria vector, were assessed in a laboratory setting. Our results show that larval densities were reduced when exposed to the sublethal doses. When exposed to Bti LC70 as larvae, the proportional hazard rate for mortality as adult females was about three times higher than in the control group. At the same LC70 dose rate, the mean wing length of the adult females increased by 12% compared to that of the control group. These findings are valuable as they demonstrate that larval exposure to Bti, even at lower doses, reduces the longevity of emerging adults which also reduces their vectorial capacity as they may not live long enough to effectively transmit the malaria parasite. In Chapter 5, we assessed whether communities would  accept and are willing to participate in community-led LSM activities. Specifically, we explored factors that would motivate community acceptance and participation in LSM. Our results show that community involvement in LSM as an additional tool for malaria control increases local awareness of malaria as a health problem, its risk factors and control strategies. The results also show that specially trained members of the community easily accepted the intervention and were more willing to participate in the associated activities than the rest of the community. Further, the findings highlight the need to make activities less demanding in terms of time and labour. It was also observed that the community needs incentives to participate in community-led interventions but though critical, forms and modes of delivery of incentives need to be further studied. In Chapter 6, we investigated whether community involvement in LSM is feasible and can result in reduced larval vector densities. Our results showed that groups from the community, which received tailored training from the research team, participated more actively in the LSM activities than the rest of the community. Also, larviciding using Bti was the more preferred component of LSM by the community than habitat modification. Interestingly, application of Bti reduced larval densities in intervention villages. The findings of this study suggest that community involvement in LSM is only feasible when the community understands their malaria risk factors and control methods. Also, the study demonstrates that community involvement in application of Bti has the potential to reduce larval densities but should be implemented after proper training of the spraying teams. In Chapter 7, the key findings of this research and the implications for community-led LSM in Malawi are addressed and recommendations for future investigations are provided. In conclusion, the results of the research described in this thesis show that participation of communities in LSM is feasible and can reduce the malaria burden via reduced larval densities

The control of malaria vectors in rice fields: a systematic review and meta-analysis.

The relatively stable aquatic conditions of irrigated lowland and rainfed rice, which is grown across 145 million hectares in more than 100 countries, are capable of generating large numbers of mosquito vectors of malaria, which causes more than 400,000 deaths per year worldwide. Many methods can control these vectors, but a systematic review has not previously been conducted. This study assesses whether larviciding, fish or intermittent irrigation can significantly reduce malaria vectors in rice fields whilst increasing rice yield. After a literature search for studies reporting the effect of larval control and rice cultivation practices on malaria vector densities in rice fields, 33 studies were eligible for meta-analysis. Larviciding was effective at reducing rice-field malaria vectors. Pooled analysis of five controlled time-series (CTS) studies with chemical insecticides showed an overall combined reduction of larval densities of 77% compared to no larviciding. Eight CTSs with biological larvicides showed a pooled reduction of 60% compared to no larviciding. Cultivating rice and fish together provided good control too: a pooled analysis of three CTSs showed an overall 82% reduction in anopheline larvae compared to no fish. Pooled analysis of four studies suggested that intermittent irrigation (using various timings and frequencies of drainage) is effective at reducing the abundance of late-stage anopheline larvae (pooled reduction = - 35%), but not overall immature abundance, compared to continuous flooding. We conclude that many interventions such as larvicides, fish and intermittent irrigation can provide riceland malaria vector control, but the critical obstacle to wider use is farmer acceptability. Future research should be led by the agricultural sector, with inputs from entomologists, to investigate malaria control co-benefits within high-yielding rice cultivation practices

Integrated Vector Management – generation and use of evidence for more effective vector control

Vector-borne diseases (VBD) such as malaria, dengue and leishmaniasis have a major public health impact primarily in low and middle income countries in the tropics. Vector control methods including long-lasting insecticidal nets and indoor residual spraying contribute substantially to control of VBDs, particularly malaria. However, progress is being hampered by a number of factors including a lack of human, infrastructural and financial resources, and is threatened by the development of insecticide resistance. The World Health Organization (WHO) strongly advocates the use of Integrated Vector Management (IVM), a policy which has the potential to overcome many of the challenges facing vector control. IVM calls for evidence-based and adaptive use of vector control tools and involvement of multiple sectors to control VBDs. This thesis brings together work on the theme of IVM and the generation and use of evidence for better vector control programming. Specifically I ask how do we develop high quality evidence to improve the effectiveness of vector control? The writer has been a principal author of a recently published WHO Toolkit for IVM in sub-Saharan Africa (Volume II of this thesis). This toolkit for vector control programme managers builds on previous WHO guidance by providing practical detail on how to plan, implement, and monitor and evaluate an IVM programme. In order to provide guidance on choice of vector control interventions in the IVM toolkit, it was necessary to systematically review the evidence from field trials of vector control tools. Two systematic reviews are presented evaluating the efficacy of insecticide-treated nets, curtains and screening against non-malaria VBDs, and the efficacy of topical repellents against malaria. These found that: i) insecticide-treated materials in the home (nets, curtains and screening) are protective against cutaneous leishmaniasis and may be protective against dengue and Japanese encephalitis, ii) topical repellents are not protective against falciparum or vivax malaria in endemic populations. Systematic reviews revealed a paucity of well-conducted efficacy studies of vector control interventions which hinders evidence-based policy-making. A critical analysis of vector control study design and conduct is presented. This analysis identified common failings with vector control trials including a lack of randomisation and blinding, poor choice of outcome measures, lack of replication, no sample size calculations and contamination between clusters in cluster-randomised trials. Many of these failings could be easily rectified to produce better quality evidence and prevent waste in research. As well as evidence-based policy making on vector control interventions, IVM calls for use of evidence throughout the lifetime of the programme through entomological and epidemiological surveillance and monitoring and evaluation to choose and target interventions, measure their effectiveness and adapt the programme over time. One entomological parameter which should be measured is insecticide resistance. A study of the spatial and temporal pattern of knockdown resistance (kdr) resistance in Anopheles gambiae s.l. in a setting of high vector control use in the Upper River Region of The Gambia is presented which found that: i) An. arabiensis was the most common member of the species complex, ii) the odds of kdr were 24 times higher in An. gambiae s.s. in villages with both IRS and LLINs and 14 times higher in villages with LLINs alone, iii) the kdr mutation was more common in mosquitoes in the second year of the study and with increasing distance from the river. The result of this work is the IVM Toolkit for sub-Saharan Africa. IVM provides a logical framework to think through vector control and advocates for a more locally tailored and adaptive approach which engages partners within and beyond the health sector. Compared to current vector control, IVM has the potential to be more effective (through evidence-based use of interventions), cost-effective (through implementation of cost effective interventions and sharing of resources across sectors), sustainable (through engagement and mobilisation of communities and the non-health sector) and ecologically sound (through the use of non-insecticide-based tools). However, there are a number of challenges to utilisation of IVM. While this thesis outlines the theoretical framework for IVM, it does not test its use by programmes, and in fact there are few good examples of IVM in practice available. Policies and organisational structures of vector control programmes are currently not in support of IVM. Lack of resources (infrastructural, human and financial) hampers implementation of this more knowledge-intensive and adaptive approach to vector control. Deeply engrained silos and lack of political support may impede partnership working within and across sectors. An increased focus on vector control in the light of the recent Zika virus disease outbreak and high-level policy changes at WHO including development of the forthcoming Global Vector Control Response should galvanise support for vector control and reorientation of programmes towards an IVM approach. IVM can be implemented if there is additional and sustained financing for vector control, an investment in human resources and infrastructure, and more commitment to working across sectors. It is important to grasp this opportunity in order to exploit fully the potential of vector control to control and eliminate VBDs in the future

Adapting to vector-borne diseases under climate change : an evidence-informed approach

Les preuves s'accumulent sur les effets des changements climatiques. Étant donné leurs impacts sur la santé, en particulier sur les maladies à transmission vectorielle, il est nécessaire de concevoir des stratégies efficaces pour adapter les programmes de gestion de risque de ces maladies. Les changements climatiques constituent un problème complexe, impliquant de multiples parties prenantes et comportant beaucoup d’inconnues. Des approches qui prennent en compte cette complexité sont ainsi nécessaires afin de faire avancer la recherche sur l'adaptation aux changements climatique basée autant sur des données scientifiques que sur des données provenant de différents intervenants. Les approches fondées sur les données probantes sont de plus en plus recherchées dans les politiques de santé et la prise de décisions, dans le but d'améliorer la santé des populations. Ces approches sont apparues en réaction aux approches improvisées, développées suite aux crises liées aux problèmes de santé publique. Elles doivent être systématiques et transparentes, et faire appel aux meilleures preuves disponibles. L'aide à la décision multicritère délibérative constitue une de ces approches. L'objectif de cette thèse était d'étudier les principales préoccupations en matière de décisions relatives à l'adaptation au risque des maladies vectorielles influencées par les changements climatiques dans deux contextes : le Québec, où les maladies vectorielles sont présentes, mais ne constituent pas la principale préoccupation, et le Burkina Faso, où les maladies vectorielles sont au contraire très préoccupantes. Les fondements théoriques de cette étude sont basés sur la science post-normale, l'adaptation aux changements climatiques et une approche d'analyse de décision multicritère. La recherche sur l'adaptation aux changements climatiques vise à influencer les politiques cherchant à réduire les risques et les impacts associés à ces changements. Dans ce cadre et dans le contexte de l'adaptation aux maladies vectorielles, trois questions clés se posent : 1) de quelles maladies nous préoccupons-nous ? 2) qui est le plus vulnérable à ces maladies ? et 3) quelles sont les mesures recommandées pour s'adapter à ces maladies ? Cette thèse contribuera à répondre à ces trois questions dans le but de faire avancer l'adaptation face aux maladies vectorielles. Pour répondre à la première question, nous avons identifié des préoccupations d'importance pour la priorisation des maladies liées aux changements climatiques au Québec et au Burkina Faso grâce à l’utilisation d’une approche délibérative multicritère d'aide à la décision. Les résultats ont démontré que, alors que des préoccupations générales sont partagées entre ces deux régions, des préoccupations plus spécifiques aux maladies diffèrent quant à elles selon le contexte, tant sur des aspects scientifiques que sur d’autres aspects partagés par les parties prenantes. Pour répondre à la deuxième question, les connaissances actuelles et les comportements de la population québécoise quant au virus du Nil occidental ont été explorés, comme étape préliminaire pour évaluer la capacité d'adaptation au risque de maladies causées par les moustiques. Nous avons considéré que la réponse au risque perçu de maladies transmises par les moustiques constituait une forme d'adaptation. Les résultats ont montré que les connaissances globales et les niveaux d'adoption comportementale sont bons et qu’il existe au moins quatre sous-groupes différents dans la population caractérisés par différents facteurs associés à l'adoption de comportements préventifs. Enfin, pour répondre à la troisième question, une approche multicritère délibérative a été utilisée pour examiner les stratégies de gestion du virus du Nil occidental au Québec, dans le cadre théorique d’une transmission accrue, et les stratégies de gestion du paludisme au Burkina Faso, dans le cadre de la transmission actuelle. De manière analogue au modèle développé pour la priorisation des maladies, cette comparaison entre les deux régions et les contextes de maladie ont permis de confirmer l’existence de préoccupations générales partagées. Cette thèse a permis de démontrer la pertinence des approches d'aide à la décision pour explorer des stratégies de gestion efficaces basées sur l'expérience des intervenants et les meilleures preuves scientifiques disponibles.Evidence is accumulating on the ongoing effects of climate change. Given the anticipated health implications, notably vector-borne disease impacts, there is a need to design effective and tailored strategies to adapt to vector-borne disease risk. Climate change is a complex problem, involving multiple stakeholders and many unknowns. As such, approaches that can embrace this complexity are needed to inform adaptation research with evidence - both scientific and stakeholder-informed. Evidence-informed approaches are being increasingly sought in health policy and decision-making in order to improve population health. Evidence-informed approaches have arisen in reaction to ad-hoc, crisis-driven responses to health problems. They recognize the need to be systematic and transparent, and make use of the best available evidence. Deliberative multicriteria decision aid is one such approach. The objective of this thesis was to study key decision concerns of importance in adapting to vector-borne disease risk under climate change in two contexts: Quebec, where vector-borne diseases are present but not the main burden of disease, and Burkina Faso, where vector-borne diseases contribute to the primary burden of disease. The theoretical underpinnings of this study are rooted in post-normal science, climate change adaptation, and a multicriteria decision analysis approach. Climate change adaptation research is aimed at informing policies to reduce risks and impacts associated with climate change. Within this framework, and in the context of vector-borne disease adaptation, three key questions arise: 1) what diseases are we concerned about? 2) who is most vulnerable and at risk to these diseases? and 3) what are recommended measures to adapt to these diseases? This thesis contributes to these three dimensions to inform adaptation to vector-borne disease. With regards to the first question, we identified concerns of importance for disease prioritization under climate change in both Quebec and Burkina Faso using a deliberative multi-criteria decision aid approach. The results showed that general concerns are shared among these contrasting contexts while specific disease priorities differ as a result of context-informed evidence – both scientific and stakeholder-shared. With regards to the second question, current knowledge and readiness of the Quebec population relative to West Nile virus was explored as a preliminary and integral step to assessing adaptive capacity to mosquito-borne disease risk. Here, response to perceived mosquito-borne disease risk constitutes a form of adaptation. The results showed that overall knowledge and behavioural adoption levels are good though at least four different subgroups exist within the population with different factors associated with preventive behaviour adoption. Finally, with respect to the third question, a deliberative multi-criteria approach was used to examine management strategies for West Nile virus in Quebec and malaria in Burkina Faso. West Nile virus strategies under current and theoretical increased transmission were explored in Quebec, and malaria management strategies under current transmission were explored in Burkina Faso. Analogously to the model developed for disease prioritization, shared general concerns were found between the contrasting country and disease contexts lending support to the practical applications of decision-aid approaches for exploring effective management strategies informed by stakeholder experience and the best available scientific evidence

Integrated malaria vector control in different agro-ecosystems in western Kenya

Malaria is a complex disease and its transmission is a function of the interaction between the Anopheles mosquito vector, the Plasmodium parasite, the hosts and the environment. Malaria control has mainly targeted the Plasmodium parasite or the adult anopheline mosquitoes. However, development of resistant parasites and mosquito vectors requires the development of other strategies, such as larval control, which can be integrated in the current control programmes. To develop a larval control programme, the local vector species and their breeding characteristics need to be known. This thesis describes the results of a study on mosquito ecology, with an emphasis on malaria vectors in different agricultural settings within two highland sites (Fort Ternan and Lunyerere) and a peri-urban area (Nyalenda) in western Kenya, and the development of practical and effective mosquito larval control strategies. To provide information about the ecology of local vectors, a longitudinal two-year study on the population dynamics and breeding characteristics of local mosquito species and malaria prevalence was undertaken in the respective study sites. In addition, community perception and knowledge on malaria, causes of malaria and the control of mosquito vectors were established through a questionnaire. This information allowed for the development of small-scale mosquito larval control strategies combining source reduction, environmental manipulation through provision of shade and biological control using predatory fish (Gambusia affinis) and application of the bio-larvicide, Bacillus thuringiensis var israelensis (Bti). The main malaria vector species, Anopheles gambiae Giles sensu stricto and An. arabiensis Patton, were both present in all sites as larvae, while An. funestus Giles was only recorded in the highland villages. The majority (86%) of mosquito breeding sites were a result of human activities. Anopheles arabiensis was the main vector species in Nyalenda, while Anopheles gambiae s.s. was dominant in Lunyerere. Lunyerere had the highest percentage (12.5%) adult indoor resting An. arabiensis mosquitoes ever recorded in the western Kenyan highlands. Fort Ternan had the highest percentage (71%) of larval An. arabiensis ever recorded at such high altitude. Plasmodium falciparum, the main malaria parasite in the region, was present in the schoolchildren cohort examined and no significant differences in malaria prevalence were observed among the study sites. The inhabitants of the respective communities regarded malaria as a burden and they expressed a willingness to take part in mosquito control, although they did not know how this could be done. A pilot study of larval control strategies conducted in Nyalenda demonstrated the feasibility of environmental and biological control methods in man-made, mostly agricultural, mosquito habitats. The larval control strategies that were applied in the highland villages led to complete elimination of both early and late instar mosquito populations and compared well with the effects of Bti application. The results suggest that the larval control strategies developed in this study will contribute significantly to a reduction in adult mosquitoes and hence, malaria transmission. Larval control strategies need to be developed that take into account the breeding habits of the local vectors as well as the suitability of habitats for a given control strategy. An integrated approach using various larval control strategies that are locally available, can easily be adopted by the communities concerned. Community involvement in disease control will lead to knowledge on how the peoples’ activities affect their health and this can empower them to take charge of their health. <br/

Modelling the impact of vector control interventions on Anopheles gambiae population dynamics

<p>Abstract</p> <p>Background</p> <p>Intensive anti-malaria campaigns targeting the <it>Anopheles </it>population have demonstrated substantial reductions in adult mosquito density. Understanding the population dynamics of <it>Anopheles </it>mosquitoes throughout their whole lifecycle is important to assess the likely impact of vector control interventions alone and in combination as well as to aid the design of novel interventions.</p> <p>Methods</p> <p>An ecological model of <it>Anopheles gambiae sensu lato </it>populations incorporating a rainfall-dependent carrying capacity and density-dependent regulation of mosquito larvae in breeding sites is developed. The model is fitted to adult mosquito catch and rainfall data from 8 villages in the Garki District of Nigeria (the 'Garki Project') using Bayesian Markov Chain Monte Carlo methods and prior estimates of parameters derived from the literature. The model is used to compare the impact of vector control interventions directed against adult mosquito stages - long-lasting insecticide treated nets (LLIN), indoor residual spraying (IRS) - and directed against aquatic mosquito stages, alone and in combination on adult mosquito density.</p> <p>Results</p> <p>A model in which density-dependent regulation occurs in the larval stages via a linear association between larval density and larval death rates provided a good fit to seasonal adult mosquito catches. The effective mosquito reproduction number in the presence of density-dependent regulation is dependent on seasonal rainfall patterns and peaks at the start of the rainy season. In addition to killing adult mosquitoes during the extrinsic incubation period, LLINs and IRS also result in less eggs being oviposited in breeding sites leading to further reductions in adult mosquito density. Combining interventions such as the application of larvicidal or pupacidal agents that target the aquatic stages of the mosquito lifecycle with LLINs or IRS can lead to substantial reductions in adult mosquito density.</p> <p>Conclusions</p> <p>Density-dependent regulation of anopheline larvae in breeding sites ensures robust, stable mosquito populations that can persist in the face of intensive vector control interventions. Selecting combinations of interventions that target different stages in the vector's lifecycle will result in maximum reductions in mosquito density.</p

Window screening, ceilings and closed eaves as sustainable ways to control malaria in Dar es Salaam, Tanzania.

BACKGROUND\ud \ud Malaria transmission in Africa occurs predominantly inside houses where the primary vectors prefer to feed. Human preference and investment in blocking of specific entry points for mosquitoes into houses was evaluated and compared with known entry point preferences of the mosquitoes themselves.\ud \ud METHODS\ud \ud Cross-sectional household surveys were conducted in urban Dar es Salaam, Tanzania to estimate usage levels of available options for house proofing against mosquito entry, namely window screens, ceilings and blocking of eaves. These surveys also enabled evaluation of household expenditure on screens and ceilings and the motivation behind their installation.\ud \ud RESULTS\ud \ud Over three quarters (82.8%) of the 579 houses surveyed in Dar es Salaam had window screens, while almost half (48.9%) had ceilings. Prevention of mosquito entry was cited as a reason for installation of window screens and ceilings by 91.4% (394/431) and 55.7% (127/228) of respondents, respectively, but prevention of malaria was rarely cited (4.3%, 22/508). The median cost of window screens was between US $21-30 while that of ceilings was between US$301-400. The market value of insecticide-treated nets, window screening and ceilings currently in use in the city was estimated as 2, 5 and 42 million US$. More than three quarters of the respondents that lacked them said it was too expensive to install ceilings (82.2%) or window screens (75.5%).\ud \ud CONCLUSION\ud \ud High coverage and spending on screens and ceilings implies that these techniques are highly acceptable and excellent uptake can be achieved in urban settings like Dar es Salaam. Effective models for promotion and subsidization should be developed and evaluated, particularly for installation of ceilings that prevent entry via the eaves, which are the most important entry point for mosquitoes that cause malaria, a variety of neglected tropical diseases and the nuisance which motivates uptake