 The purpose of this study is to measure the amount of moxidectin in subjects blood and to measure safety. This study will enroll 36 children aged 4 to 11 years 12 kg with or without Onchocerca volvulus O volvulus infection. O volvulus is the nematode, or roundworm, that causes Onchocerciasis, also known as river blindness. Each subject will receive a single dose of 4 mg moxidectin orally administered and will be followed inpatient from screening through day 13 and as outpatients through month 6. The study will take place at a single research center. 