The blackfly is a vector of onchocerciasis, also known as river blindness. A vector is an organism, such as a mosquito or fly, that transmits a disease-causing organism, such as a parasite or virus, from one host to another. In the case of the blackfly, it can transmit a parasite called Onchocerca volvulus, which can cause severe itching, skin lesions, and eventually blindness if left untreated. Onchocerciasis is a serious disease that affects millions of people in Africa, Latin America, and Yemen, and the blackfly is one of its primary vectors.