Progress in eliminating onchocerciasis in the WHO Region of the Americas: Advances in reaching the last endemic communities of the South Focus in the Bolivarian Republic of Venezuela

Overview

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.

The parasite has no environmental reservoir or natural nonhuman hosts. Microfilariae cause severe itching and disfiguring skin disease, and they may enter the eye, causing vision loss and blindness in some individuals. Ivermectin (Mectizan®) is a safe, effective oral microfilaricide that Merck Sharp and Dohme has donated1 since 1987 to control or eliminate onchocerciasis through repeated community-wide mass drug administration (MDA). The drug rapidly kills microfilariae, and repeated rounds of treatment with high coverage can permanently stop transmission by increasing the mortality of adult worms.