Progress in Eliminating Onchocerciasis in the WHO Region of the Americas: Advances Towards Interrupting the Transmission of Onchocerciasis from the Latest Preliminary Serological Assessments Conducted in Parts of the Yanomami Focus Area, 2018–2022

Human onchocerciasis (river blindness) is caused by the parasitic worm Onchocerca volvulus, transmitted by Simulium black flies that breed in fast-flowing rivers and streams. In the human host, adult male and female O. volvulus worms become encapsulated in subcutaneous fibrous “nodules”, and fertilized females produce embryonic microfilariae that migrate to the skin, where the black fly vectors ingest them during a blood meal. In the vector, the microfilariae develop into the infectious third larval stage, at which time they can be transmitted to the next human host via subsequent bites.