River blindness, medically known as onchocerciasis, is caused by a parasitic worm called *Onchocerca volvulus*. This worm is transmitted to humans through the bite of infected blackflies, which breed near fast-flowing rivers and streams—hence the name “river blindness.” When a blackfly bites a person, it deposits larvae of the worm into the skin. These larvae then mature into adult worms inside the human body, living in nodules under the skin for up to 10 years.
The adult worms produce millions of tiny larvae called microfilariae, which migrate through the skin and eyes. It is the presence and death of these microfilariae that trigger intense itching, skin changes, and inflammation. When microfilariae invade the eye, they cause damage that can lead to visual impairment and eventually permanent blindness if untreated.
The blackfly vector is crucial in the disease cycle. Only female blackflies transmit the parasite because they require blood meals to reproduce. These flies thrive near rivers and streams, which is why communities living close to such water bodies are at the highest risk. The repeated bites over time increase the chance of infection and the buildup of microfilariae in the body.
The disease is most prevalent in parts of Africa, with some cases in the Arabian Peninsula and the Americas. It affects millions of people, causing not only blindness but also severe skin conditions and, in some cases, neurological problems like epilepsy linked to the infection.
Treatment focuses on killing the microfilariae to reduce symptoms and transmission. The drug ivermectin is widely used because it kills the larvae and temporarily sterilizes the adult worms, reducing their ability to reproduce. However, because adult worms live for many years, treatment must be repeated regularly over a long period to control the disease effectively.
In summary, river blindness is caused by a parasitic worm transmitted by blackflies near rivers. The adult worms produce larvae that cause skin and eye damage, leading to intense itching and blindness. Control efforts rely on interrupting this cycle through medication and reducing blackfly exposure.
