General term for a fungus infection of the skin. Its name is derived from the particular form of the skin abnormality, which takes the form of a ring, with normal skin in the centre, occurring almost exclusively on the trunk and upper arms and legs. Fungus infections can affect hands and feet, but these take river blindness (onchocerciasis) Infestation with the nematode worm The larvae have as an intermediate host a mosquito which lives near rivers, hence the name of the disease. About 20 million people are affected, of which 250,000 are blind. Blindness occurs only in those who have been infested for many years. Slight infestation by adult worms in subcutaneous connective tissue causes itchy skin abnormalities. The larvae can cause inflammation of the eye, resulting in blindness after a number of years as a result of corneal inflammation and iritis. Slight infestation needs no treatment; blindness can be prevented by