Progress in eliminating onchocerciasis in the WHO Region of the Americas: Report from the Inter-American Conference on Onchocerciasis (‎IACO)‎ 2023

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 has been donated by Merck Sharp and Dohme1 since 1987 to control or eliminate onchocerciasis through repeated community-wide mass drug administration (MDA). The drug rapidly kills microfilariae present in the skin, prevents the release of new microfilariae by female worms for up to 5–6 months, and repeated rounds of treatment with high coverage can contribute to permanently stopping transmission by decreasing the life expectancy of adult worms.

Ivermectin treatment in the YFA in 2023

In 2023, Brazil did not reach its semiannual treatment goal in both MDA rounds (63% of its eligible population of 15 650 in the first and 67% in the second). In the semiannual approach, the Venezuela South Focus Programme reached a coverage of 86% in the first treatment round but did not reach it in the second, with 83% coverage of its semiannual eligible population of 13 630 individuals. In the 67 high-priority communities targeted with a quarterly MDA approach in 2023, coverage was 81%, 90%, 92% and 83% of the eligible population of 2287, respectively, each quarter.