Ovine Progressive Pneumonia

There are a number of causes of pneumonia in adult sheep. The "Sheep & Goat Management in Alberta - Health Module" posted on the Alberta Lamb Producers website provides additional information.

Ovine progressive pneumonia, also known as OPP and maedi-visna, is a viral disease that affects sheep of all breeds. The virus has a worldwide distribution with the exception of Australia and New Zealand, and is very widespread in North America. Ovine progressive pneumonia is closely related to the caprine arthritis encephalitis virus found in goats, which can lead to problems with eradication schemes when sheep are housed with goats. There is no known treatment or vaccine for this disease.

Production losses due to sub-clinical infection make up the biggest economic impact of ovine progressive pneumonia. Infected sheep appear to be healthy, but fail to thrive or raise lambs as they should, and carry the virus spreading it to flock mates and offspring.

The most common form of transmission of the virus is from infected mother to nursing lambs via the colostrum and milk. Transmission to the lamb while still in the uterus is considered possible, although rare. Adult to adult transmission does occur, especially in close confinement where respiratory secretions from coughing are easily contracted by another sheep. Fence-line contact and shared feed and water containers have been shown to allow for adult transmission of the virus. Using the same needle on many sheep when vaccinating or medicating is also a potential means of transmitting the virus via blood. The possibility of venereal transmission is unknown at this time.

The virus is of the retrovirus family and has an incubation period that can be up to three years. This means that a lamb exposed to the virus while nursing may not become infected for several years. To further complicate matters, an infected animal may not show clinical signs for several years. This makes detection of potentially infected animals difficult. A final diagnosis is only possible at post-mortem. Once infected, the virus will persist for the lifetime of the animal, and once clinical signs appear, the disease is always fatal.

For seed stock flocks and large confinement operations in particular, the disease can result in serious economic losses. Work with your veterinarian to decide if control or eradication is an option for your flock.