A surveillance system for lymphatic filariasis after its elimination in Sri Lanka

Lymphatic filariasis (LF) has been declared eliminated in Sri Lanka in September 2016. To maintain elimination status, a surveillance system to detect hidden endemic foci or LF resurgence is of highest priority. In this paper, we have reported an investigation of LF transmission in Trincomalee district where a surveillance program was not carried out due to 30 years of civil unrest. Proposed surveillance system included, measurement of anti-filarial IgG4 in urine of schoolchildren in areas where LF transmission could exist and assessment of circulating filarial antigen (CFA) and microfilaria (mf) in all urine antibody positive schoolchildren, their family members and 10-15 neighbours of each urine antibody positive household. Spatial distribution of the anti-filarial antibody titers in urine in a high antibody suspected area was analyzed using GPS logger data. Among 2301 school children from 11 schools studied, 41 (1.8%) urine antibody positives were found. The antibody positive rates of the schools ranged between 0 and 4.0%. Nine of the 630 (1.4%) examined became positive for CFA but were negative for mf. Although there were no mf positives, positive CFA and antibody results indicated the existence of Wuchereria bancrofti in Trincomalee. Highest antibody titres in an area correlated with the prevalences of urine antibodies and CFA. Spatial analysis showed LF transmission foci. Therefore, a combination of the non-invasive methods, urine ELISA and GPS mapping, will be a new effective surveillance system to identify hidden LF transmission foci.