Effect of a single dose of 8 mg moxidectin or 150 mu g/kg ivermectin on O. volvulus skin microfilariae in a randomized trial: Differences between areas in the Democratic Republic of the Congo, Liberia and Ghana and impact of intensity of infection

Background Our study in CDTI-naive areas in Nord Kivu and Ituri (Democratic Republic of the Congo, DRC), Lofa County (Liberia) and Nkwanta district (Ghana) showed that a single 8 mg moxidectin dose reduced skin microfilariae density (microfilariae/mg skin, SmfD) better and for longer than a single 150 mu g/kg ivermectin dose. We now analysed efficacy by study area and pre-treatment SmfD (intensity of infection, IoI). Methodology/Principal findings Four and three IoI categories were defined for across-study and by-study area analyses, respectively. We used a general linear model to analyse SmfD 1, 6, 12 and 18 months posttreatment, a logistic model to determine the odds of undetectable SmfD from month 1 to month 6 (UD1-6), month 12 (UD1-12) and month 18 (UD1-18), and descriptive statistics to quantitate inter-interindividual response differences. Twelve months post-treatment, treatment differences (difference in adjusted geometric mean SmfD after moxidectin and ivermectin in percentage of the adjusted geometric mean SmfD after ivermectin treatment) were 92.9%, 90.1%, 86.8% and 84.5% in Nord Kivu, Ituri, Lofa and Nkwanta, and 74.1%, 84.2%, 90.0% and 95.4% for participants with SmfD 10-20, > 20-< 50, > 50-< 80, > 80, respectively. Ivermectin's efficacy was lower in Ituri and Nkwanta than Nord Kivu and Lofa (p < 0.002) and moxidectin's efficacy lower in Nkwanta than Nord Kivu, Ituri and Lofa (p < 0.006). Odds ratios for UD1-6, UD1-12 or UD1-18 after moxidectin versus ivermectin treatment exceeded 7.0. Suboptimal response (SmfD 12 months post-treatment > 40% of pre-treatment SmfD) occurred in 0%, 0.3%, 1.6% and 3.9% of moxidectin and 12.1%, 23.7%, 10.8% and 28.0% of ivermectin treated participants in Nord Kivu, Ituri, Lofa and Nkwanta, respectively. Conclusions/Significance The benefit of moxidectin vs ivermectin treatment increased with pre-treatment IoI. The possibility that parasite populations in different areas have different drug susceptibility without prior ivermectin selection pressure needs to be considered and further investigated.