(OPP, lunger disease. Maedi-Visna)
Ovine progressive pneumonia is a slow developing viral disease that is characterized by progressive weight loss, difficulty in breathing and development of lameness, paralysis, and mastitis. It is very closely related to caprine arthritis-encephalitis virus (CAE) and is caused by a retrovirus. The OPP virus closely resembles Maedi-Visna which is a similar slow or retrovirus found in other parts of the world.
OPP is transmitted laterally to other susceptible animals or to offspring through ingestion of infected milk and colostrum. Veterinary diagnostic laboratory assistance is required for diagnosis. There is no treatment, but OPP can be eliminated from the herd using annual blood testing and removal of positive animals and removal of the lambs from the ewes prior to suckling.
It is estimated that over 50% of the flocks in the U.S. are infected with OPP with the number of sheep infected within a positive flock anywhere between 1% to 70%. However, the vast majority of infected sheep will never show respiratory disease or a wasting syndrome.