Urban Agriculture and Operational Mosquito Larvae Control:\ud Mitigating Malaria Risk in Dar es Salaam, Tanzania

Global commitment, political will and financial support to reduce the burden of malaria, a disease which kills about one million people each year, have reached an unprecedented level. Although global malaria eradication appears to be a distant goal, there are promising efforts towards regional control and local elimination of the disease. Sub-Saharan Africa (SSA) is the region with the world’s highest malaria burden, as well as the world’s fastest growing cities. Rapid urbanisation brings enormous challenges such as increasing poverty and malnutrition, the spread of informal settlements, inadequate sanitation and lack of access to safe water, as well as health risks. Malaria transmission in urban settings, although to a lesser extent than in rural areas, remains a significant problem. In Tanzania and many other developing countries, one response to increasing urban demand for food is urban agriculture (UA), especially in backyard gardens and larger open spaces. While urban farming is an integral part of livelihoods and food security, it may also increase the risk of vector-borne diseases, including malaria, by providing suitable grounds for mosquito breeding. However, it is unclear whether agricultural land use or rather geographical factors such as topography and hydrology lead to the creation of habitats for malaria vector mosquitoes. The overall aim of this study was to contribute to a better understanding of the importance of urban agricultural land use in the context of environmental malaria control in urban SSA, and identifying potential mitigation options. All field research for this study was conducted in 2005 and 2006 in the city of Dar es Salaam, Tanzania, and was fully integrated in the operational Urban Malaria Control Programme (UMCP), managed by the Dar es Salaam City Medical Office of Health. The main goal of the UMCP is to control mosquito larvae with the application of biological larvicides by community-based resource persons. The transdisciplinary research approach used in this study was a combination of natural and social scientific approaches, and took account of the knowledge and capacities of stakeholders in the context of the UMCP. Quantitative methods included participatory mapping of administrative boundaries, cross-sectional mapping of agricultural areas, and surveys of farmer’s agricultural practices. Qualitative methods consisted of semi-structured key informant interviews and Focus Group Discussions using interview guidelines. The theoretical framework that guided the study design and data analysis was based on the concepts of risk, resilience and threat, where risk is seen as a function of threat and resilience. In order to gain a more comprehensive understanding of factors related to malaria risk (i.e. malaria infection and disease), aspects of malaria threat (i.e. presence of breeding sites with potentially malaria-transmitting Anopheles mosquitoes) and resilience to malaria (i.e. social resilience in terms of increased competence of stakeholders in the context of the UMCP) were investigated. In a first step, the current extent and characteristics of urban agriculture were assessed. This revealed that UA is widespread in Dar es Salaam, with more than 5% of the study area used for farming in 2005. Extrapolated to the total urban area, this corresponds to almost 20 km2 of land used for urban agriculture in Dar es Salaam. Furthermore, an analysis of the spatiotemporal changes of urban agricultural use showed that urban farming is a dynamic, but not a short-lived or transitional phenomenon. The overall extent of UA did not decrease during the last two decades, despite the city’s rapid growth and densification. UA thus appears to be resilient in terms of its ability to persist in the presence of high non-agricultural pressure on land use, and its ability to recover after disturbances by spatial shifts. In a second step, a participatory mapping method was developed that allowed linking the agricultural data from 2005 with mosquito larval data from the UMCP. This was necessary in order to assess correlations of these agricultural areas with Anopheles breeding sites. At the same time, this procedure facilitated comprehensive routine larval surveillance by the UMCP. The approach involved basic use of aerial imagery and Geographical Information Systems (GIS), and was validated by mapping three urban wards of Dar es Salaam, covering an area of 16.8 km2. The procedure enabled verification and correction of cognitive sketch maps drawn by UMCP field staff as guidance for their work, and therefore complete coverage of targeted areas with larval control. It proved to be practical, affordable, and requires minimal technical skill. Thus, it can be readily integrated into malaria vector control programmes, scaled up, and adapted to urban settings elsewhere in Africa. In Dar es Salaam, the participatory mapping approach became an integral part of the novel management, monitoring and evaluation system for implementing routine larviciding developed by the UMCP. Therefore, it partly contributed to the reduction of malaria transmission by the primary vector, Anopheles gambiae s.l., by 31% (95% CI=21.6-37.6%; p=0.04). In a third step, the agricultural data was linked with the UMCP larval database. This revealed that the proportion of habitats containing Anopheles larvae was 1.7 times higher in agricultural areas compared to other areas (95% CI: 1.56-1.92). Significant geographic predictors of the presence of Anopheles larvae in gardens included location in lowland areas, proximity to rivers, and relatively impermeable soils. Significant agricultural predictors comprised specific seedbed types, mid-sized gardens, irrigation by wells, and cultivation of sugar cane or leafy vegetables. Significant negative predictors included small garden size, irrigation by tap water, rainfed production, and cultivation of leguminous crops or fruit trees. Although there was an increased risk of finding Anopheles larvae in agricultural sites, breeding sites in urban agriculture accounted for less than a fifth of all breeding sites of malaria vectors in Dar es Salaam. The identified indicators of relatively high and low odds of larval presence in agricultural areas can help improve the effectiveness of larviciding interventions. In a last step, in order to explore mitigation measures implemented within the UMCP, capacity building processes on various programme levels were analysed. By applying the Multi-layered Social Resilience framework in the context of the UMCP using a qualitative approach, it was found that exchange between and within administrative levels supported resilience-building processes in terms of mosquito breeding site elimination. “Reactive” and “proactive” capacities were successfully built among programme staff. However, more potential could be tapped among local leaders and household members, by increasing their competence in eliminating breeding sites of malaria vectors. Improving the communication skills of the programme's field workers might support such processes. Together with local leaders, they could act as multipliers of sensitisation messages. In conclusion, this study showed that urban agriculture is not only widespread in Dar es Salaam, but also a potential malaria risk with regard to breeding sites for Anopheles mosquitoes. Urban farming therefore needs to be considered by integrated vector control programmes. However, it should not be overemphasized; rather farmers should be regarded as potential assets in vector control. For example, they could be involved by planting shade trees near water bodies in agricultural areas. More generally, mitigation strategies related to environmental malaria control could build on increased participation of household members within the UMCP intervention area. This may be achieved by building capacities for breeding site elimination, for example through enhanced sensitisation of household members provided by UMCP field workers. These insights, gained by conducting transdisciplinary operational research, can provide a basis for optimising malaria control and urban planning in Dar es Salaam and other malaria-affected SSA cities with comparable climatic conditions

First things first: Mapping the extent of urban agriculture

Despite the amount of research on urban agriculture, very little is actually known about the extent of farming activities in many cities. Before municipalities can begin to develop institutional support for urban agriculture, they need to know exactly what is going on, and where. That's where GIS comes in

Commencer par le commencement : dresser la carte de l'agriculture urbaine

Nonobstant de nombreuses recherches en agriculture urbaine, la plupart des villes ignorent bien souvent quel volume d'activité celle-ci représente. Or une municipalité ne peut entrevoir le développement d'un appui institutionnel à cette forme d'agriculture sans avoir une idée préalable des endroits où elle se pratique et des cultures concernées. C'est ici que le SIG entre en scène

A Simple and Efficient Tool for Trapping Gravid Anopheles at Breeding Sites.

No effective tool currently exists for trapping ovipositing malaria vectors. This creates a gap in our ability to investigate the behavior and ecology of gravid Anopheles.\ud Here we describe a simple trap that collects ovipositing Anopheline and Culicine mosquitoes. It consists of an acetate sheet coated in glue that floats on the water surface. Ten breeding sites were selected in rural Tanzania and 10 sticky traps set in each. These caught a total of 74 gravid Anopheles (54 An. arabiensis, 1 An. gambiae s.s. and 16 unamplified) and 1333 gravid Culicines, in just two trap nights. This simple sampling tool provides an opportunity to further our understanding of the behavior and ecology of gravid female Anophelines. It strongly implies that at least two of the major vectors of malaria in Africa land on the water surface during the oviposition process, and demonstrates that Anophelines and Culicines often share the same breeding sites. This simple and efficient trap has clear potential for the study of oviposition site choice and productivity, gravid dispersal, and vector control techniques which use oviposition behavior as a means of disseminating larvicides

Community-owned resource persons for malaria vector control: enabling factors and challenges in an operational programme in Dar es Salaam, United Republic of Tanzania.

BACKGROUND: Community participation in vector control and health services in general is of great interest to public health practitioners in developing countries, but remains complex and poorly understood. The Urban Malaria Control Program (UMCP) in Dar es Salaam, United Republic of Tanzania, implements larval control of malaria vector mosquitoes. The UMCP delegates responsibility for routine mosquito control and surveillance to community-owned resource persons (CORPs), recruited from within local communities via the elected local government. METHODS: A mixed method, cross-sectional survey assessed the ability of CORPs to detect mosquito breeding sites and larvae, and investigated demographic characteristics of the CORPs, their reasons for participating in the UMCP, and their work performance. Detection coverage was estimated as the proportion of wet habitats found by the investigator which had been reported by CORP. Detection sensitivity was estimated as the proportion of wet habitats found by the CORPS which the investigator found to contain Anopheles larvae that were also reported to be occupied by the CORP. RESULTS: The CORPs themselves perceived their role as professional rather than voluntary, with participation being a de facto form of employment. Habitat detection coverage was lower among CORPs that were recruited through the program administrative staff, compared to CORPs recruited by local government officials or health committees (Odds Ratio = 0.660, 95% confidence interval = [0.438, 0.995], P = 0.047). Staff living within their areas of responsibility had > 70% higher detection sensitivity for both Anopheline (P = 0.016) and Culicine (P = 0.012): positive habitats compared to those living outside those same areas. DISCUSSION AND CONCLUSIONS: Improved employment conditions as well as involving the local health committees in recruiting individual program staff, communication and community engagement skills are required to optimize achieving effective community participation, particularly to improve access to fenced compounds. A simpler, more direct, less extensive community-based surveillance system in the hands of a few, less burdened, better paid and maintained program personnel may improve performance and data quality

Effective autodissemination of pyriproxyfen to breeding sites by the exophilic malaria vector Anopheles arabiensis in semi-field settings in Tanzania

BACKGROUND Malaria vector control strategies that target adult female mosquitoes are challenged by the emergence of insecticide resistance and behavioural resilience. Conventional larviciding is restricted by high operational costs and inadequate knowledge of mosquito-breeding habitats in rural settings that might be overcome by the juvenile hormone analogue, Pyriproxyfen (PPF). This study assessed the potential for Anopheles arabiensis to pick up and transfer lethal doses of PPF from contamination sites to their breeding habitats (i.e. autodissemination of PPF). METHODS A semi-field system (SFS) with four identical separate chambers was used to evaluate PPF-treated clay pots for delivering PPF to resting adult female mosquitoes for subsequent autodissemination to artificial breeding habitats within the chambers. In each chamber, a tethered cow provided blood meals to laboratory-reared, unfed female An. arabiensis released in the SFS. In PPF-treated chambers, clay pot linings were dusted with 0.2 - 0.3 g AI PPF per pot. Pupae were removed from the artificial habitats daily, and emergence rates calculated. Impact of PPF on emergence was determined by comparing treatment with an appropriate control group. RESULTS Mean (95%CI) adult emergence rates were (0.21 +/- 0.299) and (0.95 +/- 0.39) from PPF-treated and controls respectively (p < 0.0001). Laboratory bioassay of water samples from artificial habitats in these experiments resulted in significantly lower emergence rates in treated chambers (0.16 +/- 0.23) compared to controls 0.97 +/- 0.05) (p < 0.0001). In experiments where no mosquitoes introduced, there were no significant differences between control and treatment, indicating that transfer of PPF to breeding sites only occurred when mosquitoes were present; i.e. that autodissemination had occurred. Treatment of a single clay pot reduced adult emergence in six habitats to (0.34 +/- 0.13) compared to (0.98 +/- 0.02) in the controls (p < 0.0001), showing a high level of habitats coverage amplification of the autodissemination event. CONCLUSION The study provides proof of principle for the autodissemination of PPF to breeding habitats by malaria vectors. These findings highlight the potential for this technique for outdoor control of malaria vectors and call for the testing of this technique in field trials

Urban agriculture and Anopheles habitats in Dar es Salaam, Tanzania.

A cross-sectional survey of agricultural areas, combined with routinely monitored mosquito larval information, was conducted in urban Dar es Salaam, Tanzania, to investigate how agricultural and geographical features may influence the presence of Anopheles larvae. Data were integrated into a geographical information systems framework, and predictors of the presence of Anopheles larvae in farming areas were assessed using multivariate logistic regression with independent random effects. It was found that more than 5% of the study area (total size 16.8 km2) was used for farming in backyard gardens and larger open spaces. The proportion of habitats containing Anopheles larvae was 1.7 times higher in agricultural areas compared to other areas (95% confidence interval = 1.56-1.92). Significant geographic predictors of the presence of Anopheles larvae in gardens included location in lowland areas, proximity to river, and relatively impermeable soils. Agriculture-related predictors comprised specific seedbed types, mid-sized gardens, irrigation by wells, as well as cultivation of sugar cane or leafy vegetables. Negative predictors included small garden size, irrigation by tap water, rainfed production and cultivation of leguminous crops or fruit trees. Although there was an increased chance of finding Anopheles larvae in agricultural sites, it was found that breeding sites originated by urban agriculture account for less than a fifth of all breeding sites of malaria vectors in Dar es Salaam. It is suggested that strategies comprising an integrated malaria control effort in malaria-endemic African cities include participatory involvement of farmers by planting shade trees near larval habitats

Leitfaden für Praxisversuche

Nach Ansicht der Autoren sollen und können Versuche im eigenen Betrieb nicht wissenschaftliche Untersuchungen an Forschungseinrichtungen ersetzen. Vielmehr stellen sie eine sinnvolle Ergänzung zur Forschung an solchen Institutionen dar. Durch ein optimales Zusammenspiel beider Formen könnten so in Zukunft dem Landwirt die Informationen an die Hand gegeben werden, die er für seine erfolgreiche Betriebsführung braucht. Dieser Leitfaden für Praxisversuche deckt Experimente zur pflanzlichen Erzeugung ab. Unberührt davon lassen sich jedoch auch Versuche zur Tierhaltung, im Vermarktungsbereich oder zur Betriebswirtschaft im eigenen Betrieb durchführen. Der vorliegende Leitfaden gibt grundlegende und nützliche Informationen darüber, wie ein nicht wissenschaftlich ausgebildeter Landwirt in seinem Betrieb einfache Versuche anlegen kann, die einem Mindestmaß an wissenschaftlichen Anforderungen genügen, ohne jedoch den Landwirt zu überfordern. Dementsprechend versteht sich der Leitfaden für den Praktiker als „Hilfe zur Selbsthilfe“. Je nach Fragestellung, Ausbildungsstand und verfügbarer Zeit können Landwirte solche Praxisversuche allein durchführen oder sich Unterstützung durch ihren Berater oder andere Experten z.B. von Landesämtern und Landwirtschaftskammern, staatlichen Lehr- und Versuchsanstalten oder Universitäten holen. Der Schwerpunkt des Leitfadens liegt auf Hinweisen zur Planung und Durchführung von Experimenten im laufenden landwirtschaftlichen Betrieb. Dabei soll die Versuchsdurchführung eine Datenqualität liefern, die ein auf den gesamten Standort übertragbares Ergebnis und bei Bedarf tiefere statistische Auswertungen ermöglicht. In der Regel ist für den Landwirt in erster Linie die Gewinnung von Ergebnissen und Erkenntnissen entscheidend, die für seinen Betrieb oder Standort gelten. In den meisten Fällen sind dazu einfach zu berechnende statistische Größen wie Mittelwert und Streuungsmaß als Anhaltspunkte für die Datenauswertung ausreichend. Wir empfehlen allerdings, die Anlage der Versuche und die Erhebung der Daten in einer Weise durchzuführen, die die Möglichkeit offen hält, die Daten z. B. gemeinsam mit einem Experten vertieften statistischen Tests zu unterziehen, um ggf. eine weitere Bewertung der Daten vorzunehmen