Spatial and Temporal Heterogeneity of Malaria Transmission in sub-Saharan Africa

Mogeni, Polycarp Kambona (2017). Spatial and Temporal Heterogeneity of Malaria Transmission in sub-Saharan Africa. PhD thesis The Open University.



The past decade has seen a marked decline in malaria transmission and substantial progress towards malaria control in parts of Africa. A key tool in malaria control is the insecticide treated net (ITN). However, malaria remains a public health emergency in sub-Saharan Africa with children under five years of age bearing the greatest burden of the disease. In this thesis, I examine three sets of questions that are relevant to the changing epidemiology of malaria.

a) I investigated trends in malaria cases in Kilifi County on the Kenyan Coast over geographical area and over time, age, and the effectiveness of ITN use in the community. I observed a decline in the proportion of admitted children who had malaria parasites detected by microscopy from 1998 to 2009 as previously observed in some countries of sub-Saharan African. However, there was a steady and marked increase in the proportion of children with malaria parasites after 2009 accompanied by a shift in burden of disease from younger age groups to older age groups. Community ITN use was highly effective in reducing the risk of malaria. As transmission fell, geographical heterogeneity became
more marked.

b) I undertook an analysis of data shared from 19 studies conducted between 1996 and 2015 in 7 countries of sub-Saharan Africa to examine whether micro-geographical heterogeneity was generalizable. Hotspots were identified in all datasets, and were more marked at lower transmission intensity. Given the predictability with which hotspots occur as transmission intensity falls, malaria control programmes should have a low threshold for responding to apparent clustering of cases.

c) I then considered whether rapid diagnostic tests (RDTs) or PCR would alter detection of hotspots. Using cross-sectional studies of asymptomatic parasitaemia, I describe hotspots of malaria transmission in three sites on the Kenyan Coast using data from 8581 study participants. Microscopy and RDT missed a larger proportion of infections in low transmission settings. PCR hotspots completely overlapped with microscopy hotspots at a moderate transmission, but not at two low transmission setting. From this work, I recommend that malaria control programmes consider PCR testing for targeted control when transmission intensity is low.

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