The primary purpose of this phase 3b study is to determine the safety and efficacy of moxidectin administration twice a year, compared to once a year, in maintaining undetectable levels in skin of O. volvulus microfilaria in skin, the parasite that causes river blindness.

Secondary purposes are to determine the effectiveness of moxidectin compared to ivermectin once or twice a year in maintaining undetectable levels, or reducing levels, of skin microfilaria.

Inclusion Criteria:

• Provision of written informed consent, or assent with parental or guardian written consent.
• Mean ≥ 10 O. volvulus microfilariae/mg skin, determined by four skin snips
• Living in a village selected for the study.
• Age ≥ 12 years.
• All female participants of childbearing potential must commit to the use of a reliable method of birth control for the duration of treatment and until 3 months after completion of dosing with investigational product.

Exclusion Criteria:

• Pregnant or breast-feeding.
• Any concurrent condition that, in the opinion of the Investigator, would preclude evaluation of response to treatment or would pose undue risk to the participant's health.
• Has received ivermectin, oral diethylcarbamazine (DEC) or doxycycline (for > 2 weeks) within 6 months of Baseline.
• Has received treatment with an investigational agent within the last 30 days (or 5 half-lives, whichever is longer) prior to Baseline.
• Known or suspected allergy to ivermectin or moxidectin or their excipients.
• Self-reported planned or ongoing activities within the study period that would make it unlikely that a participant will be available for all planned treatment rounds and follow-up examinations.
• Weight > 88 kg.
• Infection with Loa loa.