Impact of Mass Drug Administration with Ivermectin, Diethylcarbamazine, and Albendazole in Elimination of Lymphatic Filariasis in Five Districts of Nepal

BackgroundNepal aims to eliminate Lymphatic Filariasis (LF) by 2030. Mass drug administration (MDA) has ceased in 53 of 64 endemic districts. In 2023, five districts with persistent LF ([≥]2% antigen prevalence) completed two rounds of MDA using a three-drug regimen (Ivermectin, Diethylcarbamazine, and Albendazole; IDA), achieving over 65% coverage. An Epidemiological Monitoring Survey (EMS) was conducted to evaluate IDAs impact. MethodsA 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. ResultsNine 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 = 0.04), but not antigen prevalence (p = 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. ConclusionNine EUs met the EMS threshold for impact assessment eligibility. Female gender and participation in the most recent MDA round were protective against microfilariae. Targeted MDA strategies focusing on men and high-risk areas are recommended.