Reaching the Criteria to Stop Onchocerciasis Mass Drug Administration: Ethiopia, Nigeria, and Uganda Pave the Way

To eliminate human onchocerciasis transmission of the filarial parasite Onchocerca volvulus (OV), endemic countries undertake a multi-step process to:

1. Identify focus areas with endemic onchocerciasis transmission,

2. Treat people at risk of OV infection within endemic ‘foci’ using mass drug administration (MDA) for at least 13 years of annual treatment with the microfilaricide ivermectin to suppress transmission,

3. Conduct post-treatment surveillance (PTS) after stopping MDA for a minimum of 3–5 years to confirm the interruption of transmission, and

4. Conduct post-elimination surveillance to confirm that transmission has been permanently interrupted.

One of the most challenging steps for endemic countries is breaking the cycle of transmission to the point where MDA can be stopped. In the World Health Organization’s (WHO’s) 2016 guidelines, WHO recommends stopping MDA only if <0.1% of larvae in parous vector Simulium black flies are found to be infective (or <0.05% of all black flies tested in pools) and <0.1 % of children under the age of 10 years test positive for antibody to the OV-16 recombinant antigen in enzyme-linked immunosorbent assays (ELISA). For a country to be declared free of human onchocerciasis, all endemic foci must demonstrate this evidence with 95% statistical confidence before stopping MDA.