Progress on elimination of lymphatic filariasis in Sierra Leone

Abdul Conteh,Santigie Sesay,Mary H. Hodges,Joseph B. Koroma,Yaobi Zhang,Jusufu Paye,Mohamed Bah,Mustapha Sonnie

doi:10.1186/s13071-018-2915-4

Abdul Conteh, Santigie Sesay + Show 6 more

Open Access

https://doi.org/10.1186/s13071-018-2915-4

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Abstract

BackgroundA baseline survey in 2007–2008 found lymphatic filariasis (LF) to be endemic in Sierra Leone in all 14 districts and co-endemic with onchocerciasis in 12 districts. Mass drug administration (MDA) with ivermectin started in 2006 for onchocerciasis and was modified to add albendazole in 2008 to include LF treatment. In 2011, after three effective MDAs, a significant reduction in microfilaraemia (mf) prevalence and density was reported at the midterm assessment. After five MDAs, in 2013, mf prevalence and density were again measured as part of a pre-transmission assessment survey (pre-TAS) conducted per WHO guidelines.MethodsFor the pre-TAS survey, districts were paired to represent populations of one million for impact assessment. One sentinel site selected from baseline and one spot check site purposefully selected based upon local knowledge of patients with LF were surveyed per pair (two districts). At each site, 300 people over five years of age provided mid-night blood samples and mf prevalence and density were determined using thick blood film microscopy. Results are compared with baseline and midterm data.ResultsAt pre-TAS the overall mf prevalence was 0.54% (95% CI: 0.36–0.81%), compared to 0.30% (95% CI: 0.19–0.47) at midterm and 2.6% (95% CI: 2.3–3.0%) at baseline. There was a higher, but non-significant, mf prevalence among males vs females. Eight districts (four pairs) had a prevalence of mf < 1% at all sites. Two pairs (four districts) had a prevalence of mf > 1% at one of the two sites: Koinadugu 0.98% (95% CI: 0.34–2.85%) and Bombali 2.67% (95% CI: 1.41–5.00%), and Kailahun 1.56% (95% CI: 0.72–3.36%) and Kenema 0% (95% CI: 0.00–1.21%).ConclusionsCompared to baseline, there was a significant reduction of LF mf prevalence and density in the 12 districts co-endemic for LF and onchocerciasis after five annual LF MDAs. No statistically significant difference was seen in either measure compared to midterm. Eight of the 12 districts qualified for TAS. The other four districts that failed to qualify for TAS had historically high LF baseline prevalence and density and had regular cross-border movement of populations. These four districts needed to conduct two additional rounds of LF MDA before repeating the pre-TAS. The results showed that Sierra Leone continued to make progress towards the elimination of LF as a public health problem.

Highlights

A baseline survey in 2007–2008 found lymphatic filariasis (LF) to be endemic in Sierra Leone in all 14 districts and co-endemic with onchocerciasis in 12 districts
In 2011, a midterm impact assessment was conducted after three annual rounds of Mass drug administration (MDA) in these 12 districts, and the results suggested progress was on track to achieve LF elimination objectives in Sierra Leone [15]
This paper presents the pre-transmission assessment survey (pre-TAS) survey results, in comparison with the baseline and midterm data and discusses whether the criteria for conducting a transmission assessment survey (TAS) for stopping LF MDA had been met in districts

Summary

Introduction

A baseline survey in 2007–2008 found lymphatic filariasis (LF) to be endemic in Sierra Leone in all 14 districts and co-endemic with onchocerciasis in 12 districts. The World Health Organization (WHO) estimates 120 million people globally are affected, with an estimated 40 million having clinically significant manifestations and the disease was identified as the second most common cause of long-term disability [7, 8]. According to the WHO recommendation, the main strategy is annual mass drug administration (MDA) of albendazole (400 mg) together with diethylcarbamazine (6 mg/kg) or ivermectin (200 μg/kg) to those known at-risk populations eligible within endemic areas [8,9,10]. Annual MDA with a minimum treatment coverage of 65% in the total at-risk population for at least five years is required to achieve the objective (microfilaraemia prevalence to below 1%) [8,9,10]. The estimate for people requiring LF MDA has dropped from 1.41 billion in 2011 to 856.4 million in 2016 [1]

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