A Comprehensive Assessment of Lymphatic Filariasis in Sri Lanka Six Years after Cessation of Mass Drug Administration

Abstract

BackgroundThe Sri Lankan Anti-Filariasis Campaign conducted 5 rounds of mass drug administration (MDA) with diethycarbamazine plus albendazole between 2002 and 2006. We now report results of a comprehensive surveillance program that assessed the lymphatic filariasis (LF) situation in Sri Lanka 6 years after cessation of MDA.Methodology and Principal FindingsTransmission assessment surveys (TAS) were performed per WHO guidelines in primary school children in 11 evaluation units (EUs) in all 8 formerly endemic districts. All EUs easily satisfied WHO criteria for stopping MDA. Comprehensive surveillance was performed in 19 Public Health Inspector (PHI) areas (subdistrict health administrative units). The surveillance package included cross-sectional community surveys for microfilaremia (Mf) and circulating filarial antigenemia (CFA), school surveys for CFA and anti-filarial antibodies, and collection of Culex mosquitoes with gravid traps for detection of filarial DNA (molecular xenomonitoring, MX). Provisional target rates for interruption of LF transmission were community CFA <2%, antibody in school children <2%, and filarial DNA in mosquitoes <0.25%. Community Mf and CFA prevalence rates ranged from 0–0.9% and 0–3.4%, respectively. Infection rates were significantly higher in males and lower in people who denied prior treatment. Antibody rates in school children exceeded 2% in 10 study sites; the area that had the highest community and school CFA rates also had the highest school antibody rate (6.9%). Filarial DNA rates in mosquitoes exceeded 0.25% in 10 PHI areas.ConclusionsComprehensive surveillance is feasible for some national filariasis elimination programs. Low-level persistence of LF was present in all study sites; several sites failed to meet provisional endpoint criteria for LF elimination, and follow-up testing will be needed in these areas. TAS was not sensitive for detecting low-level persistence of filariasis in Sri Lanka. We recommend use of antibody and MX testing as tools to complement TAS for post-MDA surveillance.

Lymphatic Filariasis Elimination in American Samoa: Evaluation of Molecular Xenomonitoring as a Surveillance Tool in the Endgame

“…Also, TAS typically use rapid antigen detection tests (Filarial Immunochromatographic Test (ICT) cards or Filarial Test Strips [4]), which might have reduced sensitivity after many rounds of MDA [5,6]. TAS has been widely used to inform important programmatic decisions including stopping or restarting MDA, but recent studies suggest that in some settings (including American Samoa), TAS might not be sufficiently sensitive for determining whether transmission has been interrupted [7,8]. …”

“…Molecular xenomonitoring has been found to be a potentially useful indicator of human LF infections with different species of mosquito vectors in diverse settings including American Samoa [11], French Polynesia [16], Egypt [12,21], Sri Lanka [8], Sierra Leone [22], and Ghana [23]. Molecular xenomonitoring is therefore potentially useful for evaluating the success of elimination programs, providing support for decisions to stop MDA, and conducting ongoing post-MDA surveillance [24].…”

“…In addition, there are currently unanswered questions about sampling strategies, limited evidence to inform the translation of MX results into operational strategies, and no clear guidelines on the thresholds of DNA prevalence that should be used to indicate likely ongoing transmission. Cut-off points of 0.25%, 0.5%, and 1% have been suggested for Culex areas [8,12,25], and 0.085% for L3 and 0.65% for any larval stage for Anopheles areas [13]. There are currently no clear recommendations for Aedes areas, but a provisional threshold of <0.1% has been suggested [26].…”

Focusing nucleic acid-based molecular diagnostics and xenomonitoring approaches for human helminthiases amenable to preventive chemotherapy

“…During an entomological survey in American Samoa, the estimated infection rate in pooled Aedes polynesiensis was 0·68% compared with the overall 0·11% rate observed by dissection of individual mosquitoes (Chambers et al 2009). Real-time qPCR has recently been used for detection of W. bancrofti in mosquito populations across the world, including Sri Lanka (Rao et al 2014), Samoa (Hapairai et al 2015), Ghana (Owusu et al 2015) and Tanzania (Irish et al 2015). Under the perspective of a programmatic use in detection of filarial DNA from both blood and mosquitoes as part of post-MDA surveillance and verification of LF elimination, the possibility of applying the same molecular test to both sample types could potentially constitute a cost and operational advantage since laboratories in developing countries will be required to be proficient in only one assay.…”

“…Molecular detection tools for Onchocerca volvulus have largely been based on the PCR amplification of the parasite-specific O-150 tandem repeat from skin snips, particularly in the assessment of skin microfilarial load reduction following PC (Alhassan et al 2015), and also from individual and pooled black flies in the Americas (Rodríguez-Pérez et al 1999). The O-150 PCR has been adapted into a qPCR format, showing increased sensitivity of detection of infection in skin snips compared with either microscopy (Fink et al 2011;Lloyd et al 2015) and also nodule palpation (Lloyd et al 2015).…”