Following the first triple-drug mass drug administration (MDA) for lymphatic filariasis in Samoa in 2018, unexpected persistence of microfilaria (Mf) positivity in 18 (15%) of 121 antigen-positive persons was observed in a nationwide household survey 1-2 months later. Of the 18 Mf positive persons, 14 reported taking the MDA, raising concerns about MDA efficacy. In 2019, 5-6 months after the 2018 survey, a monitored treatment study was done to evaluate directly observed weight-based treatment in these Mf positive individuals. Mf presence and density were assessed before and 7 days after treatment, using 1 mL membrane filtered venous blood, and 60 uL thick blood films on slides prepared from venous or fingerprick blood. All 14 participants were still Mf positive on filters from venous blood pre-treatment samples, but two were negative by slide made from the same samples. Mf were cleared completely by day 7 in 12 of 13 participants followed up, and by day 30 in the remaining participant. Filtered blood using EDTA samples (to reduce clumping of Mf) is preferred over slides alone for improving the likelihood of detecting Mf and estimating their density. The triple-drug MDA strategy was effective at clearing Mf when given and taken at the correct dose.
What is the effectiveness of appropriately dosed IDA in clearing microfilariae (Mf) from Mf positive people who (i) reported taking triple drug therapy with ivermectin, diethylcarbamazine, and albendazole (IDA) in August 2018, and (ii) did not report recently taking IDA.
This will be investigated by:
- assessing the baseline (current) Mf presence and density before re/treatment with IDA, against which post-treatment Mf presence and density can be compared
- assessing the peak plasma concentration levels of ivermectin, DEC and albendazole in treated Mf positive individuals to identify whether the recommended dosages of medications are sufficient for achieving effective plasma concentrations
- assessing Mf clearance one week following directly observed IDA re/treatment