Maedi Visna (MV) is a disease of sheep present in most sheep producing countries, including GB. It is caused by a lentivirus. A closely related virus, Caprine Arthritis Encephalitis CAE), causes a similar disease in goats. The name of the disease is formed by the two Icelandic words that describe the clinical signs it produces – maedi (‘laboured breathing’ affecting the lungs) and visna (‘shrinking’ or ‘wasting’ affecting the central nervous system). The virus can infect sheep at any age, but signs of the disease are not usually seen until at least 3 years of age. These may include pneumonia, weight loss, joint problems, mastitis and nervous signs. In goats the main clinical sign of CAE is lameness. Weight loss and shrinkage of the udder may also be present. The nervous form of the disease occurs rarely and generally only in young kids. The disease spreads easily between sheep and can cause high economic losses. A MV/CAE accreditation scheme is run by the Scottish Agricultural College.