Female Onchocerca volvolus worms live in nodules in human skin and tissues for approximately 15 years, where they produce microfilariae that can survive for up to 2 years. The microfilariae are ingested by blackflies and can cause onchocerciasis, also known as river blindness, a disease primarily found in areas near fast-flowing rivers in parts of Africa and Latin America that has led to blindness in over 500,000 people. Diagnosis involves examining skin snips or biopsies of nodules under a microscope for the presence of microfilariae or adult worms.