Abstract
.The transmission assessment survey (TAS) is recommended to determine whether cessation of mass drug administration (MDA) for lymphatic filariasis (LF) is warranted. Ministries of health typically implement TASs in evaluation units (EUs) that have had more than five rounds of annual MDA. Under TAS guidelines, sample size calculations determine a decision value: if the number of individuals testing positive exceeds this threshold, then MDA continues in the EU. The objective of this study was to determine whether fine scale geospatial covariates could be used to identify predictors of TAS failure. We geo-referenced 746 TAS EUs, of which 65 failed and extracted geospatial covariates using R to estimate odds of failure. We implemented stepwise backward elimination to select covariates for inclusion in a logistic regression to estimate the odds of TAS failure. Covariates included environmental predictors (aridity, distance to fresh water, elevation, and enhanced vegetation index), cumulative rounds of MDA, measures of urbanicity and access, LF species, and baseline prevalence. Presence of Brugia was significantly associated with TAS failure (odds ratio [OR]: 4.79, 95% CI: 2.52–9.07), as was population density (OR: 2.91, 95% CI: 1.06–7.98). The presence of nighttime lights was highly protective against failure (OR: 0.22, 95% CI: 0.10–0.50), as was an increase in elevation (OR: 0.36, 95% CI: 0.18–0.732). This work identifies predictors associated with TAS failure at the EU areal level, given the data presently available, and also identifies the need for more granular data to conduct a more robust assessment of these predictors.
Highlights
Lymphatic filariasis (LF) is a mosquito-borne parasitic infection caused by Wuchereria bancrofti, Brugia malayi, and Brugia timori
Wuchereria bancrofti are responsible for 90% of human cases, and disease transmission occurs when a mosquito bites a human infected with lymphatic filariasis (LF), acquiring the microfilariae circulating in the blood
We excluded transmission assessment survey (TAS) observations implemented in historically non-endemic evaluation units (EUs) for the purposes of confirmatory mapping, EUs that had incomplete data on the number of rounds of mass drug administration (MDA), or EUs that were unable to be geo-referenced, and for TASs implemented among EUs defined as individual communities
Summary
Lymphatic filariasis (LF) is a mosquito-borne parasitic infection caused by Wuchereria bancrofti, Brugia malayi, and Brugia timori. Wuchereria bancrofti are responsible for 90% of human cases, and disease transmission occurs when a mosquito bites a human infected with LF, acquiring the microfilariae circulating in the blood. The microfilariae develop into larvae, which can enter a new human host when the infected mosquito is feeding. The mosquito-borne larvae develop into thread-like adult-stage worms and can live 4–6 years in the human lymph system, producing microfilariae and continuing the transmission cycle.[1]. Prolonged and repeated infection can result in chronic physical manifestations that are a result of the general impact on the lymphatic system, characterized by swelling of the limbs (lymphedema) or scrotum (hydrocele).[2] Episodes of acute disability occur generally in the form of adenolymphangitis (ADL), often a precursor to lymphedema involving fever, swelling, and malaise. Historical estimates suggest that approximately 119 million people may have been infected with LF globally and another 1.3 billion reside in areas suitable for transmission in 2000.4,5 The burden of LF-related disability has been quantified, with more than 1.9 million
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