Onchocerciasis – the disease and its impact
Onchocerciasis is an eye and skin disease. The symptoms are primarily caused by microfilariae – the immature larval forms of the Onchocera volvulus worm that move around the human body in the subcutaneous tissue. Microfilariae live for 1–2 years and induce intense inflammatory responses, especially when they die.
When microfilariae die in the sub-layers of the skin, they cause skin rashes, swelling, inflammation, lesions and intense itching. Over several years, severe dermatitis can occur. The skin wastes away and loses its elasticity, giving the appearance of early ageing. This is called ‘lizard skin’. The skin can also lose some of its pigment, giving a ‘leopard skin’ appearance. This is particularly common on the lower legs.
People with onchocerciasis can have several hundred nodules on their skin. The nodules vary in size from one to five centimeters in diameter. They can cause discomfort, but are not usually painful.
Onchocercal skin disease also has an important socio-cultural impact. People with the disease often have low self esteem, experience social isolation, and worry that they will never marry. Children are distracted in school due to constant itching.
The eye disease gives onchocerciasis its common name – river blindness. Onchocercal blindness is the world’s fourth leading cause of preventable blindness after cataract, glaucoma and trachoma.
Blindness is caused when microfilariae migrate to the eye and die, causing an inflammatory response. Over time the affected area becomes opaque, leading to impaired vision and eventually blindness.
In the West African savannah, the risk of onchocercal blindness used to be very high along the riverine breeding sites of the blackfly vector. Blindness affected up to 50% of adults in some areas, and people abandoned the fertile river valleys in fear of contracting the disease. Poverty and famine increased. In the 1970’s, economic losses were estimated at US$30 million, and onchocerciasis became a major obstacle to socioeconomic development.
The socioeconomic importance of the disease was the main reason for creation of the Onchocerciasis Control Programme in West Africa (OCP) in 1975. OCP was very successful, eliminating onchocerciasis as a public health problem in 10 out of the 11 countries in which it operated.