The cause of the disease has been identified as a herpes virus. There have been reports of it being associated with weaner sheep and goats. Rabbits and Guinea Pigs cane be infected experimentally. Deer do not need to be closely associated with sheep. It is thought that the infection can be windborne for up to 1 kilometer.
Transmission is also possible from trucks used to carry sheep and then deer.
Stress is probably the major cause of initiating the disease. The incidence of the disease rises during winter in herds that have no protection from the cold. The most common manifestation of Malignant Catarrhal Fever in deer is a rapid onset of bloody diarrhoea, dark stained urine, depression and death within 48hrs. There is conjuntivitis, excessive salivation and eventually both eyes become cloudy. These animals live for a few days to a few weeks.