503 research outputs found
Dose-response tests and semi-field evaluation of lethal and sub-lethal effects of slow release pyriproxyfen granules (Sumilarv®0.5G) for the control of the malaria vectors Anopheles gambiae sensu lato.
No full textBACKGROUND: Recently research has shown that larviciding can be an effective tool for integrated malaria vector control. Nevertheless, the uptake of this intervention has been hampered by the need to re-apply larvicides frequently. There is a need to explore persistent, environmentally friendly larvicides for malaria vector control to reduce intervention efforts and costs by reducing the frequency of application. In this study, the efficacy of a 0.5% pyriproxyfen granule (Surmilarv®0.5G, Sumitomo Chemicals) was assessed for the control of Anopheles gambiae sensu stricto and Anopheles arabiensis, the major malaria vectors in sub-Saharan Africa. METHODS: Dose-response and standardized field tests were implemented following standard procedures of the World Health Organization's Pesticide Evaluation Scheme to determine: (i) the susceptibility of vectors to this formulation; (ii) the residual activity and appropriate retreatment schedule for field application; and, (iii) sub-lethal impacts on the number and viability of eggs laid by adults after exposure to Sumilarv®0.5G during larval development. RESULTS: Anopheles gambiae s.s. and An. arabiensis were highly susceptible to Sumilarv®0.5G. Estimated emergence inhibition (EI) values were very low and similar for both species. The minimum dosage that completely inhibited adult emergence was between 0.01-0.03 parts per million (ppm) active ingredient (ai). Compared to the untreated control, an application of 0.018 ppm ai prevented 85% (95% confidence interval (CI) 82%-88%) of adult emergence over six weeks under standardized field conditions. A fivefold increase in dosage of 0.09 ppm ai prevented 97% (95% CI 94%-98%) emergence. Significant sub-lethal effects were observed in the standardized field tests. Female An. gambiae s.s. that were exposed to 0.018 ppm ai as larvae laid 47% less eggs, and females exposed to 0.09 ppm ai laid 74% less eggs than females that were unexposed to the treatment. Furthermore, 77% of eggs laid by females exposed to 0.018 ppm ai failed to hatch, whilst 98% of eggs laid by females exposed to 0.09 ppm ai did not hatch. CONCLUSION: Anopheles gambiae s.s. and An. arabiensis are highly susceptible to Sumilarv®0.5G at very low dosages. The persistence of this granule formulation in treated habitats under standardized field conditions and its sub-lethal impact, reducing the number of viable eggs from adults emerging from treated ponds, enhances its potential as malaria vector control tool. These unique properties warrant further field testing to determine its suitability for inclusion in malaria vector control programmes
Ecology and Epidemiology of Integrated Malaria Vector Management in Dar es Salaam, Tanzania
No full textMalaria remains one of the major contributors to the global burden of disease with approximately 70% of the clinical malaria attacks occurring in sub-Saharan Africa. Sub- Saharan Africa has the highest risk as ideal climatic conditions for transmission coincide with occurrence of some of the most efficient malaria vectors, namely Anopheles gambiae s.s., Anopheles arabiensis and Anopheles funestus.. Even though it is estimated that by the year 2030 more than 50% of the African population will live in towns and cities, relatively little is known about urban malaria epidemiology, larval ecology and adult mosquito behaviour. Although integrated malaria control programs including environmental management and larviciding have proven successful before the Global Eradication Campaign started in 1955, they were neglected after the invention of DDT. Lately interest into these control measures has revived but it remains to be determined whether they are feasible and cost-effective in urban Africa. The overall goal of the research presented in this thesis was to enhance current understanding of urban malaria epidemiology and ecology and to take an in-depth look at the effectiveness of larviciding with Bacillus thuringiensis (Bti) in the context of the Urban Malaria Control Program (UMCP) in Dar es Salaam, Tanzania. Our findings are based on data derived from the first 3 years of the UMCP, where data collection started in March 2004. The project area includes 5 wards in each of the 3 municipalities which consist of 67 mitaa covering an area of 55 km2 in which 611,871 people lived during the population census of 2002. Achieving the UMCPs objectives fundamentally relies on three component activities: 1) Mapping and surveillance of potential Anopheles breeding sites, 2) Monitoring of adult mosquito densities, and 3) Household surveys with questionnaires and blood smears testing for malaria parasite infection. In the third year of the UMCP, beginning in March 2006, the routine application of the microbial larvicides Bti in open habitats and Bs in closed habitats was initiated in 3 of the 15 wards in the study area, adding to existing interventions such as bednets, house screening, ceiling boards, repellents, spray and coils. At the same time a detailed survey of mosquito biting behaviour, human behaviour and domestic protection measures was conducted in 12 Ten Cell Units (TCU), the smallest subunit of local government in Tanzania, which presented the highest An. gambiae s.l. densities during the early period of the UMCP surveillance system. Human landing catch (HLC) was conducted in 216 houses on an hourly basis indoors and outdoors from 6 pm till 7 am and residents were interviewed about their sleeping behaviour, where they spend their evenings and what kind of preventive measures against malaria they use. Personal protection of an insecticide treated net (ITN) was evaluated using an extension of a recently developed mathematical model. Overall An. gambiae s.l. exhibited a classical hourly biting pattern. In contrast one of the complex’s component sibling species, namely An. arabiensis, had an early biting peak before 10 pm. Both sibling species, namely An. gambiae s.s. and An. arabiensis, as well as An. funestus and An. coustani were highly exophagic. This behaviour led to a reduced personal protection against exposure to An. gambiae s.s. by ITNs which conferred 59% reduction of exposure in Dar es Salaam compared to 70% in rural Tanzania. An. arabiensis is a vector of only modest importance in Dar es Salaam which is fortunate because ITNs only conferred 38% protection against exposure to this species of mosquito. ITNs conferred slightly less protection against exposure to malaria vectors in good quality houses. This is mainly because people living in good houses tend to spend more time indoors before they go to bed. An. gambiae s.l. is the most important vector in Dar es Salaam , responsible for an EIR (entomological inoculation rate) of 1.00 infectious bites per person per year whereas An. funestus has an EIR of 0.13. Surprisingly, An. coustani also acts as a notable vector in Dar es Salaam with an EIR of 0.20 infectious bites per person per year. Malaria transmission is seasonal with two peaks of malaria prevalence during and after the two rainy seasons. Malaria prevalence was only related to EIR in children under 5 years of age, with a classical ageprevalence distribution similar to most of rural Africa. Malaria prevalence steadily declined from 2004 onwards as the use of window screenings, ceiling boards and more effective drugs like amodiaquine and artemisin-based drugs increased. ITNs (prevalence reduction estimate 20%, 95% CI 0%-36%; P=0.060; year 1) and ceiling boards (prevalence reduction estimate 22%, 95% CI 3%-38%; P=0.026; year 2) conferred modest personal protection and reduced malaria prevalence by approximately one fifth. By comparison, a much greater reduction (prevalence reduction estimate 50%, 95% CI 20%-64%; P=0.002) of malaria prevalence was achieved by larviciding with Bti. This was mainly achieved through major reductions of An. gambiae during July and August when most of the sporozoite infected mosquitoes were caught, combined with all-year-round suppression of the secondary vectors, namely An. funestus and An. coustani. This major achievement was only possible through the novel surveillance and staff management procedures developed by the UMCP to enable effective community based implementation in a decentralized manner. Standards of the surveillance improved greatly after the onset of the program with realized reaction times to vector surveillance at observations being one day, week and month at ward, municipality and city level, respectively. These results of changing biting behaviour of the main malaria vectors in urban settings and the therefore lower but still useful personal protection offered by ITNs call for additional complementary vector control methods such as environmental management or larviciding. The UMCP demonstrated that major reductions in malaria prevalence can be achieved through routine application of microbial larvicides with its new practical management and surveillance system. As these represent the early results of the program, we expect substantial improvement with time and investment. Here we demonstrated for the first time since before the Global Eradication Campaign era, a success story of a malaria control program integrating larviciding, which could be easily adapted by other African cities as a cost-effective option for malaria prevention
Community-owned resource persons for malaria vector control: enabling factors and challenges in an operational programme in Dar es Salaam, United Republic of Tanzania.
No full textUNLABELLED\ud
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ABSTRACT:\ud
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BACKGROUND\ud
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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.\ud
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METHODS\ud
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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.\ud
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RESULTS\ud
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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.\ud
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DISCUSSION AND CONCLUSIONS\ud
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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
Microbial larvicide application by a large-scale, community-based program reduces malaria infection prevalence in urban Dar es Salaam, Tanzania.
No full textBACKGROUND\ud
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Malaria control in Africa is most tractable in urban settlements yet most research has focused on rural settings. Elimination of malaria transmission from urban areas may require larval control strategies that complement adult mosquito control using insecticide-treated nets or houses, particularly where vectors feed outdoors.\ud
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METHODS AND FINDINGS\ud
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Microbial larvicide (Bacillus thuringiensis var. israelensis (Bti)) was applied weekly through programmatic, non-randomized community-based, but vertically managed, delivery systems in urban Dar es Salaam, Tanzania. Continuous, randomized cluster sampling of malaria infection prevalence and non-random programmatic surveillance of entomological inoculation rate (EIR) respectively constituted the primary and secondary outcomes surveyed within a population of approximately 612,000 residents in 15 fully urban wards covering 55 km(2). Bti application for one year in 3 of those wards (17 km(2) with 128,000 residents) reduced crude annual transmission estimates (Relative EIR [95% Confidence Interval] = 0.683 [0.491-0.952], P = 0.024) but program effectiveness peaked between July and September (Relative EIR [CI] = 0.354 [0.193 to 0.650], P = 0.001) when 45% (9/20) of directly observed transmission events occurred. Larviciding reduced malaria infection risk among children < or =5 years of age (OR [CI] = 0.284 [0.101 to 0.801], P = 0.017) and provided protection at least as good as personal use of an insecticide treated net (OR [CI] = 0.764 [0.614-0.951], P = 0.016).\ud
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CONCLUSIONS\ud
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In this context, larviciding reduced malaria prevalence and complemented existing protection provided by insecticide-treated nets. Larviciding may represent a useful option for integrated vector management in Africa, particularly in its rapidly growing urban centres
Larvicidal Effects of a Neem (Azadirachta indica) Oil Formulation on the Malaria Vector Anopheles Gambiae.
No full textLarviciding is a key strategy used in many vector control programmes around the world. Costs could be reduced if larvicides could be manufactured locally. The potential of natural products as larvicides against the main African malaria vector, Anopheles gambiae s.s was evaluated. To assess the larvicidal efficacy of a neem (Azadirachta indica) oil formulation (azadirachtin content of 0.03% w/v) on An. gambiae s.s., larvae were exposed as third and fourth instars to a normal diet supplemented with the neem oil formulations in different concentrations. A control group of larvae was exposed to a corn oil formulation in similar concentrations. Neem oil had an LC50 value of 11 ppm after 8 days, which was nearly five times more toxic than the corn oil formulation. Adult emergence was inhibited by 50% at a concentration of 6 ppm. Significant reductions on growth indices and pupation, besides prolonged larval periods, were observed at neem oil concentrations above 8 ppm. The corn oil formulation, in contrast, produced no growth disruption within the tested range of concentrations. Neem oil has good larvicidal properties for An. gambiae s.s. and suppresses successful adult emergence at very low concentrations. Considering the wide distribution and availability of this tree and its products along the East African coast, this may prove a readily available and cheap alternative to conventional larvicides
Identifying the most productive breeding sites for malaria mosquitoes in The Gambia.
No full textBACKGROUND: Ideally larval control activities should be targeted at sites that generate the most adult vectors, thereby reducing operational costs. Despite the plethora of potential mosquito breeding sites found in the floodplains of the Gambia River, about 150 km from its mouth, during the rainy season, only a small proportion are colonized by anophelines on any day. This study aimed to determine the characteristics of larval habitats most frequently and most densely populated by anopheline larvae and to estimate the numbers of adults produced in different habitats. METHODS: A case-control design was used to identify characteristics of sites with or without mosquitoes. Sites were surveyed for their physical water properties and invertebrate fauna. The characteristics of 83 sites with anopheline larvae (cases) and 75 sites without (controls) were collected between June and November 2005. Weekly adult productivity was estimated with emergence traps in water-bodies commonly containing larvae. RESULTS: The presence of anopheline larvae was associated with high invertebrate diversity (Odds Ratio, OR 11.69, 95% CI 5.61-24.34, p < 0.001), the presence of emergent vegetation (OR 2.83, 95% CI 1.35-5.95, p = 0.006), and algae (at borderline significance; OR 1.87, 95% CI 0.96-3.618, p = 0.065). The density of larvae was reduced in sites that were larger than 100 m in perimeter (OR 0.151; 95% CI 0.060-0.381, p < 0.001), where water was tidal (OR 0.232; 95% CI 0.101-0.533, p = 0.001), vegetation shaded over 25% of the habitat (OR 0.352; 95% CI 0.136-0.911, p = 0.031) and water conductivity was above 2,000 muS/cm (OR 0.458; 95% CI 0.220-0.990, p = 0.048). Pools produced the highest numbers of Anopheles gambiae adults compared with rice fields, floodwater areas close to the edge of the floodplain or close to the river, and stream fringes. Pools were characterized by high water temperature and turbidity, low conductivity, increased presence of algae, and absence of tidal water. CONCLUSION: There are few breeding sites that produce a high number of adult vectors in the middle reaches of the river in The Gambia, whereas those with low productivity are larger in area and can be found throughout the rainy season. Even though risk factors could be identified for the presence and density of larvae and productivity of habitats, the results indicate that anti-larval interventions in this area of The Gambia cannot be targeted in space or time during the rainy season
Achieving high coverage of larval-stage mosquito surveillance: challenges for a community-based mosquito control programme in urban Dar es Salaam, Tanzania.
No full textBACKGROUND\ud
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Preventing malaria by controlling mosquitoes in their larval stages requires regular sensitive monitoring of vector populations and intervention coverage. The study assessed the effectiveness of operational, community-based larval habitat surveillance systems within the Urban Malaria Control Programme (UMCP) in urban Dar es Salaam, Tanzania.\ud
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METHODS\ud
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Cross-sectional surveys were carried out to assess the ability of community-owned resource persons (CORPs) to detect mosquito breeding sites and larvae in areas with and without larviciding. Potential environmental and programmatic determinants of habitat detection coverage and detection sensitivity of mosquito larvae were recorded during guided walks with 64 different CORPs to assess the accuracy of data each had collected the previous day.\ud
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RESULTS\ud
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CORPs reported the presence of 66.2% of all aquatic habitats (1,963/2,965), but only detected Anopheles larvae in 12.6% (29/230) of habitats that contained them. Detection sensitivity was particularly low for late-stage Anopheles (2.7%, 3/111), the most direct programmatic indicator of malaria vector productivity. Whether a CORP found a wet habitat or not was associated with his/her unfamiliarity with the area (Odds Ratio (OR) [95% confidence interval (CI)] = 0.16 [0.130, 0.203], P < 0.001), the habitat type (P < 0.001) or a fence around the compound (OR [95%CI] = 0.50 [0.386, 0.646], P < 0.001). The majority of mosquito larvae (Anophelines 57.8% (133/230) and Culicines 55.9% (461/825) were not reported because their habitats were not found. The only factor affecting detection of Anopheline larvae in habitats that were reported by CORPs was larviciding, which reduced sensitivity (OR [95%CI] = 0.37 [0.142, 0.965], P = 0.042).\ud
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CONCLUSIONS\ud
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Accessibility of habitats in urban settings presents a major challenge because the majority of compounds are fenced for security reasons. Furthermore, CORPs under-reported larvae especially where larvicides were applied. This UMCP system for larval surveillance in cities must be urgently revised to improve access to enclosed compounds and the sensitivity with which habitats are searched for larvae
Community-based surveillance of malaria vector larval habitats: a baseline study in urban Dar es Salaam, Tanzania.
No full textBACKGROUND\ud
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As the population of Africa rapidly urbanizes it may be possible to protect large populations from malaria by controlling aquatic stages of mosquitoes. Here we present a baseline evaluation of the ability of community members to detect mosquito larval habitats with minimal training and supervision in the first weeks of an operational urban malaria control program.\ud
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METHODS\ud
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The Urban Malaria Control Programme of Dar es Salaam recruited and provided preliminary training to teams of Community-Owned Resource Persons (CORPs) who performed weekly surveys of mosquito breeding sites. Two trained mosquito biologists accompanied each of these teams for one week and evaluated the sensitivity of this system for detecting potential Anopheles habitats.\ud
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RESULTS\ud
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Overall, 42.4% of 986 habitats surveyed by an inspection team had previously been identified by CORPs. Agricultural habitats were detected less often than other habitats (30.8% detected, Odds Ratio [95%CI] = 0.46 [0.29-0.73], P = 0.001). Non-agricultural artificial habitats were less suitable than other habitats (29.3% occupancy, OR = 0.69 [0.46-1.03], P = 0.066) but still constituted 45% (169/289) of occupied habitats because of their abundance (51 % of all habitats).\ud
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CONCLUSION\ud
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The levels of coverage achieved by modestly trained and supported CORPs at the start of the Dar es Salaam UMCP were insufficient to enable effective suppression of malaria transmission through larval control. Further operational research is required to develop surveillance systems that are practical, affordable, effective and acceptable so that community-based integrated vector management can be implemented in cities across Africa
Development of a gravid trap for collecting live malaria vectors Anopheles gambiae s.l.
No full textBACKGROUND: Effective malaria vector control targeting indoor host-seeking mosquitoes has resulted in fewer vectors entering houses in many areas of sub-Saharan Africa, with the proportion of vectors outdoors becoming more important in the transmission of this disease. This study aimed to develop a gravid trap for the outdoor collection of the malaria vector Anopheles gambiae s.l. based on evaluation and modification of commercially available gravid traps. METHODS: Experiments were implemented in an 80 m(2) semi-field system where 200 gravid Anopheles gambiae s.s. were released nightly. The efficacy of the Box, CDC and Frommer updraft gravid traps was compared. The Box gravid trap was tested to determine if the presence of the trap over water and the trap's sound affected catch size. Mosquitoes approaching the treatment were evaluated using electrocuting nets or detergents added to the water in the trap. Based on the results, a new gravid trap (OviART trap) that provided an open, unobstructed oviposition site was developed and evaluated. RESULTS: Box and CDC gravid traps collected similar numbers (relative rate (RR) 0.8, 95% confidence interval (CI) 0.6-1.2; p = 0.284), whereas the Frommer trap caught 70% fewer mosquitoes (RR 0.3, 95% CI 0.2-0.5; p < 0.001). The number of mosquitoes approaching the Box trap was significantly reduced when the trap was positioned over a water-filled basin compared to an open pond (RR 0.7 95% CI 0.6-0.7; p < 0.001). This effect was not due to the sound of the trap. Catch size increased by 60% (RR 1.6, 1.2-2.2; p = 0.001) with the new OviART trap. CONCLUSION: Gravid An. Gambiae s.s. females were visually deterred by the presence of the trapping device directly over the oviposition medium. Based on these investigations, an effective gravid trap was developed that provides open landing space for egg-laying Anopheles
Participatory mapping of target areas to enable operational larval source management to suppress malaria vector mosquitoes in Dar es Salaam, Tanzania.
No full textBACKGROUND\ud
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Half of the population of Africa will soon live in towns and cities where it can be protected from malaria by controlling aquatic stages of mosquitoes. Rigorous but affordable and scaleable methods for mapping and managing mosquito habitats are required to enable effective larval control in urban Africa.\ud
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METHODS\ud
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A simple community-based mapping procedure that requires no electronic devices in the field was developed to facilitate routine larval surveillance in Dar es Salaam, Tanzania. The mapping procedure included (1) community-based development of sketch maps and (2) verification of sketch maps through technical teams using laminated aerial photographs in the field which were later digitized and analysed using Geographical Information Systems (GIS).\ud
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RESULTS\ud
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Three urban wards of Dar es Salaam were comprehensively mapped, covering an area of 16.8 km2. Over thirty percent of this area were not included in preliminary community-based sketch mapping, mostly because they were areas that do not appear on local government residential lists. The use of aerial photographs and basic GIS allowed rapid identification and inclusion of these key areas, as well as more equal distribution of the workload of malaria control field staff.\ud
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CONCLUSION\ud
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The procedure developed enables complete coverage of targeted areas with larval control through comprehensive spatial coverage with community-derived sketch maps. The procedure is practical, affordable, and requires minimal technical skills. This approach can be readily integrated into malaria vector control programmes, scaled up to towns and cities all over Tanzania and adapted to urban settings elsewhere in Africa
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