Belitung district, Indonesia, is endemic for lymphatic filariasis (LF) caused by zoophilic Brugia malayi. The district received 5 rounds of mass drug administration (MDA) with diethycarbamazine and albendazole (DA) between 2006 and 2010 and passed three transmission assessment surveys (TAS). Post-TAS-3 surveillance in 2021 revealed a prevalence of microfilariae (Mf) of 2.1%. This led to district-wide resumption of MDA with co-administered ivermectin, diethylcarbamazine, and albendazole (IDA). The impact of two rounds of IDA MDA was assessed using a modified IDA Impact Survey design. At baseline survey in 2022, we tested 5,161 adults in 30 clusters drawn from 26 villages. The overall Mf prevalence was 1.57% (95% CI 1.25 – 1.95), although Mf-positive individuals were only detected in 16 villages. Based on geospatial predictions, follow-up surveys were conducted in 12 villages including 1 village that was previously not chosen in the baseline randomization. Further analysis focused on the 11 villages that were surveyed three times. The overall Mf prevalence in adults at the baseline was 2.51% (95% CI 1.99 – 3.14). Prevalence of Mf carriers after one and two rounds of MDA was significantly decreased compared to the baseline (0.86% (95% CI 0.59 – 1.21) and 1.10% (95% CI 0.78 – 1.49)) respectively. Follow-up surveys showed that IDA was effective for clearing Mf, and more than 90% of the individuals in the follow-up surveys reported consumption of at least one IDA treatment. However, we detected new Mf-positive individuals during each of the follow-up surveys. In this setting, two rounds of IDA were insufficient to eliminate B. malayi . Areas with zoophilic B. malayi may need to be designated by WHO as special intervention zones for LF elimination that require additional MDA and more intense post MDA surveillances.
Supali et al. (Tue,) studied this question.