This is one of the more common diseases of farmed deer and it is usually seen in animals, which are at least one year old. It is also more frequent during winter and early spring. It is a very acute disease and farmers will often not suspect anything before they see a dead animal in the paddock. Some deer may become acutely depressed and lose condition extremely rapidly. They may also have a runny white discharge from the eyes and frequently severe bloody diarrhoea but the disease is invariably fatal. If a deer is suspected of having Malignant Catarrhal Fever, a vet should confirm the condition and the animal should be killed to avoid further suffering. The cause of Malignant Catarrhal Fever is probably a herpes virus carried by sheep, which are unaffected by the virus but can pass the disease to deer. Stress factors such as climate and under-nutrition may also help hasten the disease. There is no treatment for Malignant Catarrhal Fever but as prevention farmers should ensure that adequate nutrition is provided, particularly in mid and late winter, and that shelter is available against harsh climatic conditions. Deer should never be grazed directly with sheep and sheep should be kept well away from areas inhabited by deer, especially during winter and lambing.