Abstract
.The Sri Lankan Anti-Filariasis campaign distributed five rounds of mass drug administration (MDA with diethylcarbamazine plus albendazole) to some 10 million people in eight districts between 2002 and 2006. Sri Lanka was recognized by the WHO for having eliminated lymphatic filariasis (LF) as a public health problem in 2016. However, recent studies by our group documented pockets with persistent LF in coastal Sri Lanka, especially in Galle district. The present study was performed to reexamine an area previously identified as a potential hotspot for persistent LF (Balapitiya Public Health Inspector area, population 17,500). A community survey documented high rates for circulating filarial antigenemia (3%, confidence interval [CI]: 1.8–4.9) and microfilaremia (1%, CI: 0.5–2.5%). Circulating filarial antigenemia rates were 2.8-fold higher in males than females. High prevalence was also observed for anti-filarial antibodies in young children (5.7%, CI: 3.7–8.4%) and for filarial DNA in vector mosquitoes (5.2%, CI: 4.2–6.3%). Spatial data showed that persistent LF was dispersed across the entire study area. Other studies showed that persistent LF was not limited to Balapitiya and not solved by additional rounds of MDA. Molecular xenomonitoring studies conducted in 2016 in 22 of 168 Public Health Midwife areas in the coastal Galle evaluation unit (approximate population 600,000) found that 179 of 660 (27%) pools of Culex collected from all areas were positive for Wuchereria bancrofti DNA by quantitative polymerase chain reaction; the estimated infection rate in mosquitoes was 1.26%, CI: 1.0–1.5%. Interventions other than routine MDA will be required to remove LF hotspots in Balapitiya and in other areas in coastal Sri Lanka.
Highlights
Lymphatic filariasis (LF) has been endemic in Sri Lanka for hundreds of years with the highest rates in the “filariasis belt” in the western and southern parts of the country.[1,2,3] The AntiFilariasis Campaign (AFC, established in 1947) implemented a variety of control activities over many years that reduced infection prevalence to low levels by 1999
After providing mass drug administration (MDA) with diethylcarbamazine (DEC) for three years starting in 1999, the AFC provided five annual rounds of MDA with DEC plus albendazole in all eight endemic districts between 2002 and 2006.4–6 The AFC conducted post-MDA surveillance activities according to the WHO guidelines, and all evaluation units (EUs) in endemic districts passed transmission assessment surveys (TAS) in 2013.7 These surveys are designed to test whether filarial antigenemia prevalence in young school children is less than 2% with 95% certainty.[8]
This study has provided useful information on the assessment of persistent filarial infections and probable ongoing transmission in Balapitiya Public Health Inspector (PHI) and in other areas in the coastal Galle district EU following multiple rounds of MDA
Summary
Lymphatic filariasis (LF) has been endemic in Sri Lanka for hundreds of years with the highest rates in the “filariasis belt” in the western and southern parts of the country.[1,2,3] The AntiFilariasis Campaign (AFC, established in 1947) implemented a variety of control activities over many years that reduced infection prevalence to low levels by 1999. After providing mass drug administration (MDA) with diethylcarbamazine (DEC) for three years starting in 1999, the AFC provided five annual rounds of MDA with DEC plus albendazole in all eight endemic districts (implementation units, IU) between 2002 and 2006.4–6 The AFC conducted post-MDA surveillance activities according to the WHO guidelines, and all evaluation units (EUs) in endemic districts passed transmission assessment surveys (TAS) in 2013.7 These surveys are designed to test whether filarial antigenemia prevalence in young school children is less than 2% with 95% certainty.[8] prior studies by our group have shown that TAS was not sensitive for detecting ongoing transmission of Wuchereria bancrofti in many areas in Sri Lanka,[9] and this is likely to be true in other areas where LF is transmitted by Culex mosquitoes. Based on the encouraging TAS results and other criteria, the WHO recognized that Sri Lanka had eliminated LF as a public health problem in 2016 but recommended that the country continue surveillance efforts and intervention to clear residual infections in foci with persistent infections.[10,11]
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