<qa>  What is the nematode that causes Onchocerciasis?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. 