Impact of mass drug administration with Ivermectin, Diethylcarbamazine, and Albendazole in elimination of lymphatic filariasis in five districts of Nepal

Nepal aims to eliminate lymphatic filariasis (LF) by 2030. Mass drug administration (MDA) has ceased in 53 of the 64 endemic districts. Following failure to pass the pre-Transmission Assessment Survey of antigenemia prevalence, five districts completed two rounds of MDA using a three-drug regimen (Ivermectin, Diethylcarbamazine, and Albendazole; IDA) and achieved over 65% coverage of the total population in 2023 and 2024. An Epidemiological Monitoring Survey (EMS) was conducted to evaluate IDA's impact. A cross-sectional EMS was conducted 9 months post-MDA in 11 evaluation units (EUs) across five districts, using two sites per EU (n = 22). A total of 6,829 individuals aged ≥20 years were sampled via multi-stage methods, with ≥300 blood samples per site. Data on demographics and MDA participation were collected. LF antigen testing was followed by night blood microfilariae testing in antigen-positive samples. Analysis included non-parametric tests, logistic and mixed-effects models accounting for site-level clustering, and penalized regression (lasso and ridge) to assess predictor importance and manage multicollinearity. Nine of 11 EUs passed EMS. Two EUs in Kapilvastu failed due to ≥1% microfilariae prevalence in at least one site. Microfilariae prevalence was negatively correlated with site MDA coverage (p-value 0.04), but not antigen prevalence (p-value 0.8). Overall, 4.63% of participants were antigen-positive and 0.34% were microfilariae-positive (ratio 14:1). Being female (OR 0.12; 95% CI: 0.04-0.36) and participation in latest MDA round (OR 0.34; 95% CI: 0.15-0.77) were associated with lower microfilariae prevalence. Suboptimal impact of MDA was observed in two EUs based on microfilariae prevalence and may reflect insufficient treatment compliance. Two additional rounds of MDA with directly observed treatment are recommended to improve adherence. Female sex and participation in the most recent MDA round were associated with reduced odds of microfilaremia. Targeted strategies focusing on men and other identified risk groups may enhance program effectiveness.