The Impact of Vector Control for Malaria on Lymphatic Filariasis in Tanzania



Weaver, AM
(2018) The Impact of Vector Control for Malaria on Lymphatic Filariasis in Tanzania. PhD thesis, University of Liverpool.

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Abstract

In Tanzania, lymphatic filariasis (LF) caused by the filarial worm W. bancrofti is co-endemic with malaria and shares common mosquito vectors of the Anopheles species. LF mapping to estimate prevalence in 2004 determined the entire country was LF-endemic. However, by 2009 it was questionable whether LF transmission persisted in some districts that had not yet initiated mass drug administration (MDA) to interrupt transmission. Over the same period, national scale-up in distribution of insecticide-treated nets (ITNs) and focalised scale-up of indoor residual spraying (IRS) was underway. These interventions aimed at reducing vector populations should plausibly facilitate interruption of LF transmission, however this has not been thoroughly investigated in Tanzania. This research project sought to 1) examine predicted LF risk and trends in vector control coverage on a national scale in Tanzania, 2) investigate vector control coverage on a local scale in the Lake Zone of Tanzania, and 3) assess LF exposure and its predictors in the Lake Zone. First, secondary data analyses confirmed the risk of LF is highly variable throughout Tanzania. Nationally, household ITN ownership increased from 38% in 2007-08 to 92% in 2011-12 but decreased to 65% in 2015-16 based on Demographic and Health Survey (DHS) and Malaria Indicator Survey (MIS) data. Focalised scale-up of IRS in the Lake Zone followed the same trend (4% to 12% to 5%, respectively). Spatial analysis of ITN ownership and IRS coverage revealed significant hotspots of low and high vector control coverage. Second, in the Lake Zone, three cross-sectional household surveys conducted in six villages found a significant overall decrease in household net ownership from 73% to 50% between 2011-2013. Scale-up of IRS reached 94% of households surveyed in targeted villages by 2013. Notably, IRS was found to be significantly negatively associated with net ownership. Third, children 2-7 years of age in the six villages were sampled for the presence of antibodies to the W. bancrofti antigen Wb123. Baseline Wb123 seroprevalence varied markedly by village, ranging from 7% to 52%. Overall, a significant decrease in Wb123 seroprevalence from 28% in 2011 to 18% in 2013 was observed. Household net ownership was found to be significantly associated with the decline in Wb123 seropositivity. However, trends in net ownership and Wb123 seroprevalence at the village-level were variable. This study documents positive antibody responses to Wb123 in children born during the study, indicating recent LF exposure in a region considered to not have ongoing LF transmission. Notwithstanding the variable coverage and decline in net ownership in some villages, net ownership was found to be significantly associated with LF exposure. These findings underscore the potential for vector control to contribute to reductions in LF transmission and the need for increased coordination between malaria and LF programmes.

Item Type: Thesis (PhD)
Divisions: Faculty of Health and Life Sciences
Depositing User: Symplectic Admin
Date Deposited: 18 Jul 2019 09:01
Last Modified: 08 Sep 2021 07:20
DOI: 10.17638/03029093
Supervisors:
URI: https://livrepository.liverpool.ac.uk/id/eprint/3029093