Elimination of human onchocerciasis: progress report, 2025–2026

Overview

Onchocerciasis is caused by the filarial nematode Onchocerca volvulus and transmitted through the bites of blackflies (Simulium spp.). Adult worms live in subcutaneous nodules, where the females release millions of microfilariae (first-stage larvae, L1) that migrate through the skin and eyes, causing intense itching, disfiguring skin disease and, after prolonged exposure, visual impairment and irreversible blindness. Early exposure to infection in childhood has also been associated with onchocerciasis associated epilepsy. Microfilariae ingested by a blackfly during a blood meal develop in the fly, over 6–12 days, through L2 to the infective L3, which is inoculated into another person at a subsequent bite. More than 99% of the people requiring preventive chemotherapy (PC) for onchocerciasis live in 26 countries in Africa; the remainder live in Brazil, the Bolivarian Republic of Venezuela, and Yemen. In 2025, 255.7 million people required PC for onchocerciasis, of whom 180.3 million were treated, representing 70.5% global coverage, the highest number of people ever treated for onchocerciasis in a single year.

By the end of 2025, mass drug administration (MDA) with ivermectin had been stopped in 310 implementation units (IUs) previously affected by active transmission,and 38 million people who once required PC were living in a reasthathad completed, or wereunder, post-treatment surveillance (PTS); most of these are in Nigeria (28.0 million), Uganda, Ethiopia and Mali (Figure 6). Of the 1665 IUs requiring MDA in 2025, 1350 (81.1%) delivered it, and 92.6% of these achieved effective coverage. Angola, Gabon and Sudan did not implement MDA in 2025, Gabon because of the risk of serious adverse events inindividuals co-infected with Loa loa; the report from Chad had not been received at the time of publication. Geographical coverage remained low in Cameroon (17.1%), Togo (21.9%) and Yemen (24.4%). In Cameroon, the low coverage illustrates the consequences of abrupt changes in external funding: MDA had been planned in 123 IUs with support from external donors, which was suspended in January 2025 after the annual plans had been approved. The Government adopted a mitigation plan, but national funds were released only in October 2025, too late for treatment to be organized before the end of the year, and the shipment of ivermectin was delayed while funding remained uncertain. MDA was delivered only in the 21IUs for which other partners provided support. The transition that followed the closure of the USAID neglected tropical disease (NTD) programme showed that countries can sustain delivery by integrating MDA into routine health services and other campaigns,8 but integration requires time to plan and budget. Partners are therefore encouraged to move towards multi-year planning and to provide catalytic funding aligned with nationally owned plans, so that a change in external support does not disrupt treatment.