Identifying, characterizing, and targeting the reservoir of malaria transmission in Southern Tanzania.

Malaria continues to be a leading cause of morbidity and mortality in countries where it is endemic. While dramatic progress has been achieved globally, recent global malaria reports suggested that overall global progress has stalled since 2014. The plateau in improvement, particularly in high transmission settings of Africa, is associated with several factors, including inadequate coverage and use of the interventions, poor health service coverage, changes in vectors bionomics and insecticides resistance to malaria vectors. In addition, many high transmission countries have insufficient community based interventions to reduce malaria morbidity and mortality. Barriers to progress are associated with uncoordinated surveillance systems, low socioeconomic and living standards as well as inadequate adherence of the affected population to interventions. This hinders the efforts to achieve the overall goal of malaria elimination in many malaria endemic settings, highlighting the need for overall health system improvement to allow for innovative control and surveillance techniques. Furthermore, it necessitates a better understanding of malaria transmission dynamics. In order to meet this challenge, we must delve deeper into the underlying malaria transmission dynamics.
The proposed PhD project was embedded within a tripartite pilot project between China-United Kingdom-Tanzania. The project was about Malaria control in Rufiji district, Tanzania, that started in September 2015. The overarching goal of the PhD project was to study the dynamics of malaria transmission and evaluate the impact of community-based malaria reactive case detection strategy in strengthening the transmission-reduction of human malaria infections in areas with high coverage of LLINs. To achieve the project's goal, four specific objectives were specified. This matches to the project chapters' conclusions in this thesis.
In Chapter three of this thesis, the effectiveness of implementing a community-based testing and treatment plan to reduce the malaria burden in moderate to high transmission areas is analyzed. The "1-3-7" surveillance and response model developed in China, which prompted the development of this initiative and subsequent adoption of the 1,7-malaria Reactive Community-based Testing and Response (1,7mRCTR) approach, is a novel method for implementing the WHO-T3 and surveillance intervention to eliminate malaria. However, the 1-3-7 model is more effective in China, where the goal is to eradicate the disease, than in Tanzania, where the bulk of the population still has moderate to high transmission.
The 1,7-mRCTR is locally-tailored for reporting malaria cases on day one and intervention on day seven, with community-based testing and treatment in high-burden areas stratified based on weekly data from health facilities. In the same district, control areas with comparable epidemiology (no 1,7-mRCTR) were selected and monitored for the duration of the project. After two years of implementing the 1.7 mRCTR, the prevalence of parasites in the target areas was reduced by 66 percent above and above the benefit provided by national measures already in place. Despite the fact that new technology and techniques may be required to eradicate malaria in stable transmission areas of Sub-Saharan Africa, this experiment proved that a locally tailored approach could help to expedite malaria control and elimination efforts. In addition, it highlight the opportunities of validating the results and possibilities of scaling up 1,7-mRCTR approach in other settings within Tanzania, and other African countries for accelerating malaria control and elimination across Africa.
In chapter four of this dissertation, the household cross-sectional survey data gathered prior to 1,7-mRCTR intervention were used to describe and characterize the malaria prevalence and the associated exposures risk . In the context of the Tanzania Demographic and Health Survey and Malaria Indicator Survey (TDHS-MIS) 2015-16, this study’s findings are discussed. The findings highlight the importance of national malaria monitoring, and its ramifications for present malaria management strategies. The prevalence of malaria varied by ward, ranging from 5.6 percent to 18 percent, with the average prevalence reported by this study (13 percent) being higher than the reported by the RDHS-MIS national (7.3 percent). Based on the findings of this chapter, t is important for the new malaria control plans to be effective in sustaining gains and accelerating progress towards the end goals in the fight against malaria will depend on clearing parasitaemia and ensuring that poverty is eleviated Importantly, programs intended to improve malaria interventions for the currently recognized vulnerable groups should be modified to include other groups observed with highest parasitaemia.
Chapter five investigated and assessed one of the extremely sensitive epidemiological study of malaria transmission (host preference by malaria vectors). In addition to being a significant predictor of malaria transmission patterns, this indicator is essential for determining the appropriateness and efficacy of vector control interventions and for predicting malaria transmission patterns. Using the direct host-preference experiment, the host preference of the primary malaria vector species, Anopheles arabiensis and Anopheles gambiae sensu stricto, was examined in two distinct ecological contexts in Tanzania. In contrast to historical accounts, the data indicate that urban An. arabiensis showed a stronger preference for cattle than rural An. arabiensis, but An. gambiae showed no preference for either people or animals under the same conditions. To achieve malaria eradication, we must have a deeper understanding of the prevalent vectors, their feeding behavior in varied ecological situations, and their feeding preferences. This will allow us to more effectively design and implement locally-tailored, high-impact, integrated interventions.
Anopheles mosquito species composition, abundance, and spatial-temporal variability must be thoroughly understood in order to optimally exploit high-resolution malaria vector control strategies. Community-based mapping of residual malaria vector densities to support malaria elimination efforts in southeastern Tanzania is discussed in Chapter six. The findings highligth the changing composition of vector species through time, as well as the presence of many malaria vector species at the village scale, which is characterized by a wide spectrum of ecological variation. Human biting rates (HBR) in the study wards ranged from 1.5 to 73 bites per person every night. Characterization of Anopheles vectors indicated disparities between villages and wards in the distribution of Anopheles gambiae s.l., Anopheles funestus, and Anopheles coustani. This study's findings give evidence-based information that is essential for planning and implementing vector control actions in a local setting, complementing the results of Chapter four. In addition, the findings highlight the significance of comprehending and incorporating vector bionomics data into surveillance and response systems in order to successfully implement the ongoing micro-stratification of malaria strata.
Surveillance is acknowledged as an intervention and considered instrumental in accelerating global malaria elimination efforts. However, all available evidence to date supports the incorporation of surveillance as in intervention in low endemicity areas, with no evidence comes from moderate to high endemicity areas. Therefore, this PhD project is the first attempt to develop a surveillance and response strategy in moderate to high transmission setting. The findings aline the current Tanzania mid-term review of the national malaria control as well as with the goals Global Technical Strategy 2015-2030 (GTS) and the High Burden to High Impact (HBHI) initiative, which both reiterated the importance of tailoring intervention approaches to the sub-national local context in order to accelerate progress toward malaria reduction and elimination. Behaviour ecology matters and so does evolutionary biology in human-modified environment, the spatial-temporal variation findings in vector composition at a fine scale level of village and the reduced human-biting preference of the primary malaria vectors collected from two distinct characterized with different ecological features is an example illustrating why regular surveys of mosquito compositions and behaviour need to be incorporated in malaria surveillance. Furthermore, support that, in regions with a high malaria incidence, the convention interventions should be maintained, while prioritizing taiolored approach based on the local contex.