The effect of treatment on the number of adult worm nests detected by ultrasonography. The mean (±SEM) number of worm nests in scrotal lymphatics pretreatment and at 6, 12, 24, and 36 months posttreatment is shown. Only men with detectable worm nests in the scrotal lymphatics at baseline were examined at follow-up. Annual ivermectin plus albendazole (IA) treatment significantly reduced worm nests from baseline at 12, 24, and 36 months (P = .015, P < .001, and P < .001; paired Wilcoxon rank sum test). A single treatment with ivermectin plus diethylcarbamazine plus albendazole (IDA) resulted in significantly greater reductions in worm nest counts relative to annual treatment with IA for all time points posttreatment (P < .001). The significance of this difference was determined by the Mann–Whitney U test. The 5 participants in the IDA arm who were retreated with IDA at 24 months were included in the worm nest analysis, because the additional round of treatment had almost no additional effect on worm nests (see text). Abbreviations: ALB, albendazole; DEC, diethylcarbamazine; IA, ivermectin plus albendazole; IDA, ivermectin plus diethylcarbamazine plus albendazole; IVM, ivermectin; SEM, standard error of the mean.