Ovine Pulmonary Adenocarcinoma (OPA), also known as Jaagsiekte, is a transmissible viral disease of sheep which causes lung tumours. As these tumours grow they impair lung function and secrete large volumes of fluid. OPA is spread through the aerosol route but also through colostrum and milk. Over time sheep with OPA lose condition and develop progressive respiratory signs, often leading to respiratory distress and eventually death. The disease is most commonly observed in 3 to 4 year old sheep but can be seen in sheep less than a year old.
Ultrasonography can be used to differentiate chronic lung lesions in adult sheep including detection of OPA lesions as small as 2 cm in diameter. Trans-thoracic ultrasound examination can be considered for a second opinion on an initial diagnosis of OPA, for screening purchased adult flock replacements for OPA, or for screening sheep in a known OPA-affected flock.
Detection of OPA lesions by ultrasound examination allows culling at an earlier stage than recognition of clinical signs by the farmer, and enables culling while the sheep is still in good body condition, fit to travel and has greater value for slaughter. In addition, the ability to identify affected animals using ultrasound scanning reduces transmission of OPA as tumours are picked up quicker, before OPA is spread to other sheep in the flock.
Scanning for OPA before weaning allows the farmer to identify which lambs belong to any positive ewes (if they were not recorded at birth), so that they are not kept as replacements. Young lambs are highly susceptible to OPA infection, therefore removing any lambs born to positive ewes will decrease the chances of keeping infected animals in the flock.
For OPA scanning we have our own sheep crate so that each animal can be restrained safely for scanning. Two vets will attend, meaning that one of us can scan from each side of the animal, allowing us to scan up to 100 sheep per hour. Any sheep where lung lesions are observed at scanning can then be marked and removed from the flock. Any farmers with cases of sudden death, wasting or respiratory signs are invited to phone their nearest branch to discuss OPA scanning with one of our vets.