Programmatic use of molecular xenomonitoring at the level of evaluation units to assess persistence of lymphatic filariasis in Sri Lanka

BACKGROUND:Sri Lanka's Anti Filariasis Campaign distributed 5 rounds of mass drug administration (MDA with DEC plus albendazole) to all endemic regions in the country from 2002-2006. Post-MDA surveillance results have generally been encouraging. However, recent studies have documented low level persistence of Wuchereria bancrofti in Galle district based on comprehensive surveys that include molecular xenomonitoring (MX, detection of filarial DNA in mosquitoes) results. The purposes of this study were to demonstrate the use of MX in large evaluation units (EUs) and to field test different mosquito sampling schemes. METHODOLOGY/PRINCIPAL FINDINGS:Galle district (population 1.1 million) was divided into two EUs. These included a coastal EU with known persistent LF and an inland EU with little persistent LF. Mosquitoes were systematically sampled from ~300 trap locations in 30 randomly selected clusters (health administrative units) per EU. Approximately 28,000 Culex quinquefasciatus were collected with gravid traps and tested for filarial DNA by qPCR. 92/625 pools (14.7%) from the coastal EU and 8/583 pools (1.4%) from the inland EU were positive for filarial DNA. Maximum likelihood estimates (MLE) for filarial DNA rates were essentially the same when the same number of mosquito pools were collected and tested from 75, 150, or 300 trap sites (range 0.61-0.78% for the coastal EU and 0.04-0.07% for the inland EU). The ability to use a smaller number of trap sites reduces the cost and time required for mosquito sampling. CONCLUSIONS/SIGNIFICANCE:These results suggest there is widespread persistence of W. bancrofti infection in the coastal Galle EU 8 years after the last round of MDA in 2006, and this is consistent with other data from the district. This study has shown that MX can be used by national programs to assess and map the persistence of W. bancrofti at the level of large EUs in areas with Culex transmission

Reassessment of areas with persistent Lymphatic Filariasis nine years after cessation of mass drug administration in Sri Lanka.

Sri Lanka was one of the first countries to initiate a lymphatic filariasis (LF) elimination program based on WHO guidelines. The Anti-Filariasis Campaign provided 5 annual rounds of mass drug administration (MDA) with diethylcarbamazine plus albendazole in all 8 endemic districts from 2002-2006. Microfilaremia (Mf) prevalences have been consistently <1% in all sentinel and spot-check sites since 2006, and all evaluation units passed school-based transmission assessment surveys (TAS) in 2013. We previously reported results from comprehensive surveillance studies conducted in 2011-2013 that documented low-level persistence of Wuchereria bancrofti in 19 high risk areas in 8 endemic districts. We now present results from repeat surveys conducted 3 to 4 years later in 6 areas that had the strongest LF signals in the prior study.The surveys assessed prevalence of filarial antigenemia (CFA) and Mf in communities, CFA and anti-filarial antibody in school children (ages 6-8), and filarial DNA in Culex mosquitoes (molecular xenomonitoring, MX). Three study areas had significantly improved infection parameters compared to the prior study, but three other areas had little change. MX was more sensitive for detecting W. bancrofti persistence, and it was a better predictor than other parameters. Adult males accounted for more than 80% of infections detected in the study.These results suggest that W. bancrofti transmission was near the break point in some of the areas studied in 2011-13. LF is likely to decline to zero without further intervention in these areas, while other areas may require further intervention. Long term surveillance may be needed to verify W. bancrofti elimination in areas like Sri Lanka with efficient transmission by Culex. Test and treat or other programs targeting adult males plus bed net promotion may be more effective than MDA for clearing remaining hotspots of transmission in Sri Lanka

Summary of <i>Wuchereria bancrofti</i> infection parameters in Peliyagodawatta in 2008, 2011 and 2015.

<p>Summary of <i>Wuchereria bancrofti</i> infection parameters in Peliyagodawatta in 2008, 2011 and 2015.</p

Estimated filarial DNA rates in <i>Culex quinquefasciatus</i> pools in 2 evaluation units (EU) in Galle, Sri Lanka.

<p>Estimated filarial DNA rates in <i>Culex quinquefasciatus</i> pools in 2 evaluation units (EU) in Galle, Sri Lanka.</p

Filarial DNA rates in <i>Culex quinquefasciatus</i> in 2 evaluation units (EU) in Galle district, Sri Lanka.

<p>Filarial DNA rates in <i>Culex quinquefasciatus</i> in 2 evaluation units (EU) in Galle district, Sri Lanka.</p

Percentages of mosquito trap locations in coastal PHM areas that yielded mosquito pools that were positive for filarial DNA by qPCR.

<p>Bars with the same color show results from PHMs within a single MOOH area. Twenty-two % of trap locations captured mosquitoes with filarial DNA, but some locations had much higher rates.</p