Evaluation of Microfilaremic Individuals after Mass Drug Treatment with Ivermectin, Diethylcarbamazine, and Albendazole for Lymphatic Filariasis in Papua New Guinea

After mass drug administration (MDA) for lymphatic filariasis, which involved a single coadministered dose of ivermectin plus diethylcarbamazine and albendazole (IDA), concerns arose regarding individuals who remained microfilaremic. This situation raised questions about the efficacy of the drugs and whether some individuals had not ingested them. In East New Britain Province, Papua New Guinea (PNG), where 81.7% of the population received IDA, 10 individuals were found to have microfilaremia 12 months after the first round of MDA in an area that had a high baseline of microfilaremia (n = 29 microfilariae [Mf] positive pre-MDA). Of these 10 individuals, 7 reported having taken the IDA medication. When Mf detection was repeated 18 months later, all 10 individuals remained Mf positive. Additionally, three more Mf-positive household members were identified, and they also reported taking the IDA. These Mf-positive individuals were then retreated with IDA under direct observation. At 7 and/or 14 months after retreatment, all initially Mf-positive individuals, except for one, were found to be Mf free. Upon further questioning, it was revealed that all but one individual admitted to not taking the initial MDA. Thus, IDA effectively clears Mf in this region of PNG, and the persistent microfilaremia after MDA is primarily because of individuals failing to take the medications as prescribed.