Onchocerciasis, also known as river blindness, is a disease caused by a parasitic worm called Onchocerca volvulus. This worm is transmitted to humans through the bites of infected blackflies, which are commonly found near fast-flowing rivers. The infection can lead to severe itching, skin rashes, and in some cases, vision loss or blindness due to damage to the eyes. The disease primarily affects people in certain regions of Africa, Central America, and Yemen. Efforts to control and eliminate onchocerciasis include mass drug administration of the medication ivermectin, which helps reduce the number of worms in the body and prevents the spread of the disease.