• Area under the concentration versus time curve (zero to infinity) of moxidectin [ Time Frame: Pre-dose to Week 12 ]
  Moxidectin concentration in plasma collected at pre-specified intervals after dosing with oral moxidectin determined using a validated liquid chromatography-mass spectrometry(MS)/MS method.
• Maximum observed plasma concentrations (Cmax) of moxidectin [ Time Frame: Hour 0 to Hour 8 ]
  Moxidectin concentration in plasma collected at pre-specified intervals after dosing with oral moxidectin determined using a validated liquid chromatography-mass spectrometry(MS)/MS method.
• Incidence and severity of adverse events [ Time Frame: Day 0 to Week 24 ]
  Incidence and severity of adverse events, assessed by the Division of AIDS (DAIDS) Table for Grading the Severity of Adult and Paediatric Adverse Events, Version 2.1.

• Experimental: Cohort 1: 12-17 years
  Moxidectin 8mg per oral, single dose
  Intervention: Drug: Moxidectin
• Experimental: Cohort 2: 8-11 years
  Moxidectin 8mg (or lower dose) per oral, single dose
  Intervention: Drug: Moxidectin
• Experimental: Cohort 3: 4-7 years
  Moxidectin single dose, determined by population pharmacokinetic modelling including data from Cohorts 1 and 2
  Intervention: Drug: Moxidectin

Inclusion Criteria:

1. Aged 4 to 17 years, inclusive:

   1. Cohort I: 12 to 17 years;
   2. Cohort II: 8 to 11 years;
   3. Cohort III: 4 to 7 years;
2. Live in a region designated by the World Health Organization (WHO) as endemic for O. volvulus infection (World Health Organization, 2019). Specifically, participants will be recruited from the Kpassa sub-district of the Nkwanta North district.The specific communities will include Wii, Jagri-Do, and Azua where mass drug administration with ivermectin for onchocerciasis commenced in October 2017;
3. Willing and able to remain at the study clinic from Screening up to Day 7;
4. Provision of parental or guardian written informed consent and assent / lack of expression of 'deliberate objection' (as appropriate for age);
5. Females of childbearing potential must commit to using a reliable method of contraception as per local family planning guidelines from Baseline (pre-treatment on Day 0) until approximately 6 months after treatment with study drug.

Exclusion Criteria:

1. History of serious medical or psychiatric condition which, in the opinion of the investigator, would put the subject at increased risk by participating in the study or jeopardize study outcomes;
2. Known or suspected concurrent clinically significant renal, cardiac, pulmonary, vascular, metabolic (thyroid disorders, adrenal disease), immunological disorders or malignancy, congenital heart disease, chronic lung disease;
3. Has received an investigational product within 28 days or 5 half-lives of Baseline, whichever is longer;
4. Has received ivermectin or any other anti-helminthic treatments within 28 days of Baseline;
5. Has received a vaccination within 7 days of Baseline;
6. Known or suspected hypersensitivity to macrocyclic lactones or excipients used in the formulation of moxidectin;
7. Poor venous access;
8. Unable to swallow tablets (flat oval, 8.0 millimeters (mm) x 4.5 mm x 3.0 mm);

9. Weight:

   1. Cohort I (12 to 17 years): < 30 kg;
   2. Cohort II (8 to 11 years): < 18 kg;
   3. Cohort III (4 to 7 years): < 12 kg;

10. Clinically relevant laboratory abnormalities at Screening, including:

    1. Hemoglobin < 9.5 grams per deciliter (g/dL);
    2. Neutrophil (granulocyte) count < 1.5 x 109/L;
    3. Platelet count < 110 x 109/L;
    4. Alanine aminotransferase (ALT) > 1.5 times the upper limit of normal range (ULN);
    5. Total bilirubin > 1.5 times ULN;
11. Hepatitis B, Hepatitis C, or human immunodeficiency virus (HIV) positive;
12. Known or suspected malaria or other ongoing viral, bacterial, or plasmodium infection at Screening and/or Baseline;
13. Loa loa co-infection;
14. Unwilling, unlikely or unable to comply with all protocol specified assessments;
15. For females of child bearing potential, pregnant or breastfeeding, or planning to become pregnant;
16. Previous enrolment in this study;
17. Is a sibling of another child already enrolled in this study.