India targets to eliminate lymphatic filariasis (LF) in alignment with the global goals. By 2024, 106 out of a total of 345 endemic districts have passed all three serial transmission assessment surveys (TAS) and are under post-mass drug administration (MDA) surveillance for a variable period. However, the current epidemiological situation of LF is not known in these districts. With increased mobility of population from the endemic districts currently under MDA to these post-MDA areas, resurgence of LF in these areas cannot be ruled out. Therefore, a study is planned to understand the current LF status in areas under post-MDA surveillance with the following objectives: (1) To assess the epidemiological situation of LF in terms of human and vector infection prevalence in selected evaluation units (EUs) under different durations of post-MDA phase and (2) to estimate the filarial infection (in terms of filarial antigen and microfilaria) among migrants (from endemic districts) in these EUs.

This cross-sectional study will measure the filarial infection in (1) adult population aged ≥20 years (following the WHO 2025 protocol for monitoring and evaluation of MDA) among general population (n=3150 per EU), (2) migrant population (aged 2 years and above) in the post-MDA area originating from endemic areas (n=1000 per EU) and (3) vectors (n=7500 per EU) using molecular xenomonitoring (MX) to confirm sustenance of transmission interruption or identify any potential risk of resurgence in three EUs under post-MDA phase. In one MDA-naive EU that shares borders with endemic districts, filarial infection status will be assessed in (1) school children aged 9–14 years (as per WHO mini-TAS protocol, n=480), (2) migrants (aged 2 years and above) from endemic areas (n=1000) and (3) vectors (n=7500). EU-wide prevalence of microfilaria, circulating filarial antigen and vector infection rates with 95% CIs will be estimated. Multivariate logistic regression analysis will be carried out to find factors associated with LF positivity. In addition, knowledge, attitude and practice surveys will also be conducted among the adult migrants (n=1000 per EU). Thirty in-depth interviews will be conducted among the migrants, local community and health workers (in each EU) and the results will be suitably analysed and triangulated. The study results will enable the national programme to confirm sustenance of transmission interruption or assist in taking a decision to reinitiate MDA in these areas under post-MDA surveillance. It will also enable devising specific strategies to treat migrants.

This study has been approved by the institutional ethics committee (IHEC 03-0824/N/F). A workshop will be held with all stakeholders to disseminate the study findings.