Ivermectin, a parasiticide that long ago proved its worth in veterinary medicine, became one of the most effective tools for control programs against human filarial diseases in the 1980s. It is provided at no cost, is effective against microfilariae (blocking their transmission) and can be administered annually as a single oral dose with virtually no side-effects: these considerations led the WHO to officially declare eradicable two endemic filarial diseases (among the major endemic diseases worldwide), onchocerciasis and lymphatic filariasis.