Abstract
Following the first triple-drug mass drug administration (MDA) for lymphatic filariasis in Samoa in 2018, unexpected persistence of microfilaria (Mf) positivity in 18 (15%) of 121 antigen-positive persons was observed in a nationwide household survey 1–2 months later. Of the 18 Mf positive persons, 14 reported taking the MDA, raising concerns about MDA efficacy. In 2019, 5–6 months after the 2018 survey, a monitored treatment study was done to evaluate directly observed weight-based treatment in these Mf positive individuals. Mf presence and density were assessed before and 7 days after treatment, using 1 mL membrane filtered venous blood, and 60 uL thick blood films on slides prepared from venous or fingerprick blood. All 14 participants were still Mf positive on filters from venous blood pre-treatment samples, but two were negative by slide made from the same samples. Mf were cleared completely by day 7 in 12 of 13 participants followed up, and by day 30 in the remaining participant. Filtered blood using EDTA samples (to reduce clumping of Mf) is preferred over slides alone for improving the likelihood of detecting Mf and estimating their density. The triple-drug MDA strategy was effective at clearing Mf when given and taken at the correct dose.
Highlights
Lymphatic filariasis (LF) is a helminth worm transmitted by mosquitoes
Samoa is divided into four administrative regions, with ~19% of the population living in Apia Urban Area (AUA), 35% in Northwest Upolu
Of the 18 Mf-positive people identified in 2018 SaMELFS survey, 17 gave information in 2019 about mass drug administration (MDA) participation, and 14 participants were enrolled in the monitored treatment study involving blood sampling
Summary
The adult worms live in the lymphatic system, potentially causing chronic disability due to limb and scrotal swelling. A mated pair of adult worms lives for 5 to 7 years and can produce millions of microfilariae (Mf) that circulate in peripheral blood. The number of LF infected persons worldwide in 2000 is usually estimated to have been 130 million [1], a revised update recently generated using new modelling methods using surveys from 1990 to 2018 suggested that as many as 199 million people may have been infected in 2000 [2]. The. Global Programme to Eliminate Lymphatic Filariasis (GPELF) has conducted an intensive mass drug administration (MDA) programme since 2000 to interrupt transmission of LF [3], and the burden of infection is estimated to have been reduced dramatically to to 70 million infections in 2018 [1,2]. By 2020, 7.7 billion MDA treatments had been delivered and 17 countries or territories (eight of which are in the Pacific region [4]) have been validated as having eliminated LF as a public health problem [3,5]
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