The Mectizan Donation Program is working to eliminate onchocerciasis (commonly known as river blindness) and lymphatic filariasis (commonly known as elephantiasis). 

Onchocerciasis: (ˌäŋ-kō-ˌsər-ˈkī-ə-səs) is a parasitic disease endemic in six countries in Latin America (Brazil, Colombia, Ecuador, Guatemala, Mexico, and Venezuela), in 30 countries in Africa, and in Yemen. The filarial worm that causes onchocerciasis is Onchocerca volvulus, which is  transmitted through the bites of infected blackflies of the species Simulium. These flies carry the immature larval forms of the parasite and transmit it from human to human. In the human body, the larvae form nodules in the subcutaneous tissue, where they mature to adult worms. After mating, the female adult worm can release up to 1000 microfilariae a day. These move through the body, and when they die they cause a variety of conditions, including blindness, skin rashes, lesions, intense itching and skin depigmentation. 

Lymphatic Filariasis: (lim-fat-ik fĭl'ə-rī'ə-sĭs) is a parasitic disease endemic throughout the world, primarily in Africa, India, and the Pacific islands. In Africa, LF is caused by the parasitic thread-like worm, Wuchereria bancrofti, and is transmitted to humans through the bites of mosquitoes. Long-term infection with LF can lead to painful and disfiguring chronic enlargement of the arms and legs of people of all ages. It also causes severe swelling in the genitals of males; a condition known as hydrocele. The disease is commonly called “elephantiasis” because of the elephant-like appearance of swollen limbs in those most severely affected.