The effect of bi-annual community-directed treatment with ivermectin on the incidence of epilepsy in onchocerciasis endemic villages in South Sudan: a study protocol oleh Gasim Abd-Elfarag, Makoy Yibi Logora, Jane Y. Carter, Morrish Ojok, Jackson Songok, Sonia Menon, Ferdinand Wit, Richard Lako, Robert Colebunders