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Subject: search.filters.subject.Mosquitoes--Control

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    Assessing relationship between human settlement patterns a malaria risk in a residual transmission setting in south-eastern Tanzania
    (2019) Kaindoa, Emmanuel W
    Background: Spatial targeting of interventions is increasingly recognized as essential for malaria control, particularly in areas aiming for elimination. The associations between house characteristics and malaria transmission is known, but gaps remain on whether transmission is also influenced by factors such as distances between households or the degree to which houses are clustered. It is also important to identify new interventions that can be implemented by targeting critical points in the biology of major malaria vectors and common characteristics of human settlements. Such efforts will be essential to complement current major tools. Aims: This study had the following aims; (i) understand how households densities and their distances influence malaria transmission the study area , (ii) identify housing-related factors affecting residual transmission risks in the area (iii) assess opinions of residents on how house characteristics, settlement patterns and other environmental factors influencing malaria transmission, and (iv) identify effective complementary approaches that could be used to improve malaria control in these residual transmission area with high coverage of basic interventions such as long lasting treated nets. Methodology: A mixed methods approach was used, which included: (i) indoor and outdoor mosquito collections from fixed as well as randomly selected households over 12 months, (ii) characterization of physical and microclimatic conditions of the houses and surrounding environmental variables, (iii) assessing effects of spatial clustering of households on malaria transmission risks, and (iv) assessing community concerns regarding household and environmental factors influencing transmission. During these studies, swarms of Anopheles mosquitoes were discovered for the first time in this area. Therefore, additional quantitative and qualitative observations were made to characterize the swarms and assess how they could be targeted to complement malaria control efforts. Key findings: Despite the expansive use of LLINs in the area, factors associated with housing characteristics and settlement patterns as well as people’s perceptions contribute to persistent malaria transmission, and will need to be addressed for eventual elimination to be reached. The main findings of this study were as follows: (i) household occupancy influenced indoor mosquito density (ii) high house densities increased Anopheles biting risk but mosquito density declined as distances between houses increased beyond 50m; (iii) abundance of the vector Anopheles arabiensis peaked during high rainfall months (February-May), but An. funestus densities remained stable into the dry season (May-August); (iv) there were higher indoor densities of An. arabiensis and An. funestus in houses with mud walls compared to plastered or brick walls, open eaves compared to closed eaves and unscreened windows compared to screened windows; (v) most respondents were aware of associations between their house characteristics and malaria risks but carrying out improvements was constrained by financial costs and other household priorities; (vi) in all our surveys, An. funestus mosquitoes contributed approximately 85% of ongoing malaria transmission in the areas, even when occurring in far smaller densities than An. arabiensis; and (vii) with regards to complementary interventions, small scale studies demonstrated that mating swarms of both An. arabiensis and An. funestus could be readily identified and characterized (in this case by volunteer community members), and that targeting the swarms using aerosol spraying could possibly reduce overall biting risk in the communities. Conclusions: This study yielded evidence that malaria transmission risks are significantly lower when the distances between houses are high. Variation in malaria transmission risk within a village might be important for planning and implementing spatially targeted interventions. With limited resources, malaria control efforts must be prioritized in locations with significantly higher risk in order to obtain maximum benefit. Thus, the distances between houses should be considered when planning malaria vector control strategies. Furthermore, the overall clustering of indoor densities of major disease-transmitting mosquitoes is significantly associated with household occupancy and its spatial distribution within the villages. Further research is needed to assess the potential of using this information for predicting, identifying and targeting the most intense foci of mosquito-borne disease transmission based on household occupancy. Understanding the factors influencing malaria transmission at a small scale is crucial for planning malaria control interventions. Malaria transmission heterogeneity does not only exist on a large scale, but also at small scales, which may be influenced by small variations of environmental features, such as seasonality. These variations should be considered when improving malaria control interventions. While An. funestus showed variation in density during the year, numbers of mosquitoes remained high throughout the dry season, whereas An. arabiensis showed a definite peak in the rainy season with a subsequent drop during the dry season. Further studies are required to investigate the survival strategies of major malaria vectors during the dry season. Understanding this particular feature of An. funestus may lead to the design of new control strategies or improve existing interventions so as to reduce the malaria burden in such rural areas. This study also documented high mosquito densities in mud-walled houses compared to houses with brick or plastered walls. These findings further indicate the necessity of considering house improvement as a malaria control strategy. While the community members had fairly high awareness that improved houses were associated with reduced mosquito nuisance, many families in rural areas are living in poorly constructed houses. It is therefore necessary to consider inter-sectoral collaborations to integrate housing into health policies in Tanzania. Further studies are also needed to provide epidemiological evidence on how housing design affects malaria transmission. Furthermore, community-based house improvement programs should be promoted, including simple, scalable and affordable house improvements for the populations living in high malaria endemic areas in rural communities. Generally, this study has generated information which sets the basis for further studies on the relationship between the exact house location and malaria transmission risk in rural malaria endemic countries.
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    Outdoor malaria transmission: human activities and the risks of mosquito bites in rural communities of Mogorogoro region, Tanzania
    (2019) Moshi, Irene Richard
    Rationale Malaria prevention and control can be attained through a combination of strategies, including vector control, responsive health systems for prompt and accurate diagnosis and treatment, community access to information and interventions, and well-financed malaria control programmes. Disease prevention and control programmes depend mostly on the nature of disease transmission; therefore, this research (together with other research) helps to determine appropriate measures to prevent the target populations from the risks of acquiring infection. Historically, malaria control strategies had focused on indoor malaria transmission, with interventions aimed at reducing transmission from an endophilic and endophagic vector. In general, frontline interventions to reduce risk and prevent transmission included long-lasting insecticide Nets (LLINs) and insecticide residual spraying (IRS) but also prompt diagnostic tests and treatment. As a result of the roll-out of these strategies, many countries have experienced a tremendous decrease in malaria transmission, giving them hope to consider the possibility of malaria elimination. Outdoor malaria transmission has always existed in forests, fields, and around houses and animals, depending on vector species and preferred habitat, behaviour and host availability (animal or humans). Notably, there has been an increase in malaria transmission as a result of the increased outdoor host-seeking behaviour of mosquitoes that previously fed indoors. This has been associated with an increased proportion of malaria mosquitoes biting outdoors, resistance to pyrethroids (commonly used on ITNs/LLINs) occupational factors including migratory farming activities and changes in land use. The change in vector habitat and behaviour, and consequent sustained transmission of malaria, is a growing public health concern that jeopardizes existing vector control strategies in malaria-endemic countries including those in Africa. Although there has been growing advocacy for new research on vector control and interventions, minimal consideration has been given to the contribution of human practices and behaviour to outdoor malaria transmission. Feasible malaria prevention and control programmes need integrative approaches that take into account all contributing factors to the risks of malaria transmission, both indoor and outdoor, and the allocation of appropriate and effective interventions. In Tanzania, most malaria prevention and control programmes depend on donor funding and have focused on the prevention and control of malaria indoors. Despite research findings that indicate insecticide resistance and increasing outdoor biting by malaria vectors, outdoor malaria transmission has not been addressed within the aim and strategies for malaria control nor incorporated into the current strategies of the National Malaria Control Programme (NMCP). This reluctance to address “outdoor malaria transmission” is likely because it is a relatively new phenomenon and there are few funds available to be dedicated to interventions for preventing outdoor malaria transmission . This doctoral dissertation addresses some of the factors driving outdoor malaria transmission in areas where frontline interventions such as LLINs are widely used. I hypothesize that community knowledge on outdoor malaria transmission and prevention, and a range of behaviours and practices, might contribute to risk of infection. The four broad aims of this PhD project were to describe and analyse: community perceptions on outdoor malaria transmission; the interventions that people use while outdoors; the activities and practices that people undertake outdoors that expose them to mosquito bites; and the reasons for such practices being conducted outdoors. Methods The study was conducted in four villages in Kilombero Valley (two villages from each of the two districts Kilombero and Ulanga, from February 2015 to September 2016. A mixed method study was undertaken, based on a convergent parallel design approach whereby both qualitative and quantitative data collection strategies were conducted concurrently in the same phases of the research process. The mixed methods included entomological collections of mosquitoes by using modified CDC light trap and miniaturized double net trap (DN-Mini), and a range of social research methods to provide data to allow for indepth understanding of this topic. Specifically, in addition to observations of community activities and informal conversations with participants from the study communities, a) 40 in-depth interviews were conducted, with ten respondents selected from each village, b) eight key informant interview were conducted, with leaders/respected individuals from the community, and c) focus group discussions which were conducted with members of the study communities. Semi-structured interview guides were used to conduct all the in-depth interviews (IDIs), key informant interviews (KII) and focus group discussions (FGDs) (see guides at the end of the main texts). The interview guides were used to guide the researcher/data collectors during the conversations with adults/heads of selected household, leaders of the community and wider population respectively, to capture people’s knowledge, perceptions, and attitudes toward outdoor malaria transmission. Collection of entomological data was done by using the Centres for Disease Control and Prevention (CDC) light traps. However, the use of CDC light traps was not very efficient for indoor-outdoor biting risks comparisons so the data were complemented by additional mosquito collections using a miniaturized double net trap (DN-Mini). Mosquito biting rates of all Anopheles species collected were analyzed, and logistic regression (LR) was performed separately for each Anopheles species to determine the rate of exposure to the risk of malaria transmission as per identified activities. Using graphing and analysis in R statistical software, mosquito biting rates were analysed with the use of generalized linear mixed-effects models (GLMM) separately for each species, accounting for both fixed and random factors, with log-linked Poisson error distribution, using the lme4 package in R statistical package. A structured observation guide was also used to document all activities that were conducted outdoors, and their frequencies were correlated with the host-seeking mosquitoes collected. Mosquito collection was conducted parallel to documentation of human outdoor activities hourly from 6:00 pm to 7:00 am. To assess community knowledge, identify interventions used and activities and practices in which people engaged, thematic content analysis was used for all interviews and focus group discussions, and for notes from observations, with themes identified and responses assessed as per identified themes. Key Findings The results show that there is limited knowledge on outdoor malaria transmission among people in the study villages. The emphasis on adherence to interventions has concentrated on the prevention of indoor transmission through the use of frontline interventions. The main sources of information on the prevention of malaria, which still focuses on indoor malaria transmission, are information from healthcare workers in hospitals, road and radion advertisements, fliers, and media broadcasts by the National Malaria Control Programme (NMCP) in collaboration with different donors. Prevention of outdoor malaria transmission is not included in the strategies for malaria prevention within the NMCP. While everyday domestic activities take place outdoors throughout the year, other outdoor activities such as celebrations occur seasonally and are associated with different religious, social and cultural purposes. Those that take place on a daily basis at the household level expose people on a continuing basis to outdoor mosquito biting, thus increase the risks of malaria transmission. The study results show that peridomestic activities are conducted outdoors during the evening when the host-seeking mosquitoes (malaria vectors including both Anopheles Gambiae s.l and Anopheles funestus) were collected are prevalent and actively biting. The seasonality catch of host-seeking mosquitoes indicates that during the dry season, the highest biting peak was observed among An. gambiae s.l. at 20:00 hrs while among An. funestus the highest peak was observed at 21:00hrs. During the wet season the highest peak biting time among An. gambiae s.l. was observed at 22:00 and 19:00hrs, but there was very limited amount of mosquito density. For An. funestus, the biting rate was low throughout the night with a slight peak between 22:00hrs and 0:00hrs. When comparing biting patterns indoors and outdoors, the study found that during the dry season, the biting rates for An. gambiae indoor started to peak at 19:00hrs with the highest peak at 21:00hrs, while for An. funestus there was steady biting pattern with a slight increase between 2:00hrs and 3:00hrs. During the wet season, the biting rate among An. gambiae s.l. started to peak at 19:00hrs with highest peak at 22:00hrs hours, when there was a very limited amount of human activities indoors, while among An. funestus the biting rates were still low with a slight increase at 22:00hrs hours to 0:00hrs, again, when there was a very low frequency of human activity indoors since some families sleep around 21:00hrs to 22:00hrs. Activities that took place at these times exposed people to the risk of mosquito bites; frequent exposure increased their risks of infection. Seasonal, cultural gatherings and ceremonies are mostly conducted outdoors during the times when the host seeking mosquitoes are actively outdoors. During these activities and ceremonies, people hardly use interventions to prevent themselves from mosquito bites, thus putting people at risk of malaria infection and transmission. Although most gatherings are conducted during the dry season when there is lower vector density, gatherings associated with mourning and funerals are conducted year-round. The wet season has high mosquito density, so the risks of being bitten and infected are particularly high during this period. Attending social gatherings and ceremonies is of great importance to people in the study communities, and their engagement maintains unity, cooperation and social cohesion. There is poor access to interventions that can be used outdoors, despite the growing evidence of increased outdoor feeding and the risks of outdoor malaria transmission. House structures characteristically have minimal or no amenities like kitchens, bathrooms, and living rooms, this contributes to spending more time outdoor conducting activities such as cooking, eating, resting, conversing and, above all, socializing. Houses have poor ventilation and during the dry season, when the ambient temperature is especially high, the houses become very hot due to the absence of ceiling boards indoors. People often find it unbearable to spend time indoors, and so people spend most of their time outdoors. Additionally, most houses have unscreened windows, eaves, and doorways, thus allowing mosquitoes easy entrance into houses; this contributes to the risk of exposure to mosquito bites indoors. Implications Minimal knowledge of outdoor malaria transmission risks and little or no consideration of risk or prevention of infections contributes to people’s exposure to mosquito bites outdoors. Lack of attention to aspects of outdoor malaria transmission by the NMCP further hinders the integration of appriopriate strategies for malaria prevention and control. The NMCP continues to be silent on integrating these risks in malaria prevention strategies, and this jeopardizes the reduction and elimination of malaria in the country. In the study community, cultural and religious gatherings for both Christians and Moslems were conducted outdoors, but this is less significant than the changes in host-seeking mosquitoes and increases in outdoor biting, which continue to put people at risk of malaria infections year round. Social practices that involve communities, during a range of celebrations bring about socialization, improve unity and cooperation, and provide members of the community with material and financial benefits. These practices enable the study community to maintain social cohesion. Such activities cannot be actively discouraged, since these are practices that are tied to people’s identity. However, improved promotion of and access to interventions for both indoor and outdoor transmission will help to reduce the risk of malaria transmission and complement existing indoor interventions for malaria prevention and control.
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    The effects of low temperatures on metabolic rates in Anopheles quadriannulatus
    (2018) Ngwenya, Duduzile K
    The effects of low temperatures on the metabolic rates of Anopheles quadriannulatus were investigated by measuring the rate of carbon dioxide emission (VCO2) at different temperatures using a closed respirometry system. In general, the metabolic rates of A. quardiannulatus decreased with decreasing ambient temperatures. However, the decreases were not uniform over the temperature range of 30 °C and 10 °C. Mean VCO2 measured at 30 °C and sometimes at 25 °C, were statistically different from those measured at other temperatures. Surprisingly, at 15 °C and 10 °C, the mean VCO2 were statistically similar. It was found that metabolic rates of the mosquitoes were affected differently if a 5 °C reduction in temperature occurred at 30 °C and when it occurred at 15 °C. Thus, a 5 °C drop in temperature at 30 °C and 15 °C did not yield similar percentage decrease in metabolic rates. Age was found not to impact on the metabolism of mosquitoes except at 10 °C and 15 °C in blood fed mosquitoes (both mated and unmated). Lack of a correlation between age and metabolic rates in these mosquitoes was a result of constant body masses as mosquitoes aged. Mean VCO2 of four days old mosquitoes in different mating and feeding states were found to be significantly differently only at 10 °C. Mated and blood fed mosquitoes from this age group retained constant metabolic rates despite changes in temperature. The finding that A. quadriannulatus is not capable of significantly dropping its metabolic rates at low temperatures (15 °C-10 °C) is an indication that the species most probably lacks a physiological overwintering mechanism. Consequently, its survival and longevity is highly compromised during winter. Thus, it can be concluded that if adult A. quadriannulatus can overwinter in cooler parts of sub-Saharan regions, it does so using non-physiological mechanisms. Otherwise, this species and related members of Anopheles gambiae overwinters in developmental stages other than adulthood. In this way, these mosquitoes are able perpetuate their populations post winter season.
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    The evaluation of Bacillus thuringiensis subspecies israelensis based biopesticides for the control of southern African malaria vectors
    (2012) Ketseoglou, Irene
    Malaria, one of the most deadly vector-borne diseases in the world, is transmitted by the bite of an infected female Anopheles mosquito. Since there are several problems arising from current control programs, alternative control strategies for malaria-carrying vectors are required. The objective of this thesis was to evaluate a recombinant Anabaena sp. strain PCC 7120, Anabaena PCC 7120#11 (PCC 7120#11), as an agent to control southern African malaria vectors. Select Bacillus thuringiensis subspecies israelensis (Bti) toxin genes, cry4Aa and cry11Aa, had previously been cloned into Anabaena sp. strain PCC 7120. Evaluation of the potential of PCC 7120#11 and Bti as control agents of southern African malaria vectors required the evaluation of the larvicidal activity of PCC 7120#11 and Bti against several important malaria vectors. This study showed that all five of the African anopheline species evaluated in laboratory bioassays (Anopheles gambiae, Anopheles arabiensis, Anopheles funestus, Anopheles quadriannulatus, and Anopheles merus) were susceptible to Bti, whereas PCC 7120#11 exhibited high larvicidal activity against four of the five anopheline species. The low larvicidal activity of PCC 7120#11 against An. funestus could be due to the absence of the other Bti toxins in PCC 7120#11 or differences in the structure and/or density of specific midgut toxin receptors for the Cry4Aa or Cry11Aa proteins. The Standardized Aquatic Microcosm (SAM), a synthetic multi-species system consisting of a chemically defined medium with the same species and concentration of photosynthetic microorganisms (PMOs) and invertebrates, was used to comprehensively evaluate the effects of Bti and PCC 7120#11 in an aquatic environment. The SAM experiments showed that Bti was non-toxic to the invertebrates evaluated and did not significantly affect any of the other variables evaluated in the microcosms. Bti was shown to be an environmentally friendly control agent.