Ovine pulmonary adenocarcinoma (OPA), also known as Jaagsiekte, is an infectious lung tumour caused by a virus which affects sheep.
There is no treatment or vaccine and, once clinical signs appear, the disease is always fatal. When the disease is first introduced into a flock, losses are high, up to 20 per cent of stock.
With aggressive culling of thin ewes and any with signs of respiratory disease, the losses fall, but continue to account for a few per cent of sheep each year.
OPA is typically introduced to a flock through purchased sheep which are infected, but not showing clinical signs.
It appears to be increasingly common throughout the UK, but the true prevalence of disease is unknown.
Confirmation is by post-mortem examination with histopathology on lung tissue. Sheep with OPA often have secondary bacterial pneumonia which may mask OPA pathology.
Recently, ultrasound scanning of the chest of sheep to identify the disease before clinical signs develop, has been used, but is not widely available.
Last year a pilot study was completed to develop and evaluate a diagnostic test on nasal swabs from thin ewes to screen flocks for OPA.
This was a collaboration between Biobest Laboratories and Moredun Research Institute. In this study, the new test on nasal swabs was evaluated, which detected the virus only in infected flocks.
The virus was not detected in any flocks which were free of disease.
Rebecca Mearns, senior veterinary adviser with Biobest, says: “With more validation, this nasal swab PCR test could form the basis for a flock screen to identify low-risk flocks and facilitate an OPA assurance scheme.
“It would enable farmers to identify if the infection is present in their flock and take control measures to minimise losses.
“The 70-90 per cent of flocks estimated to be free of the disease would be able to buy replacement breeding stock from screened negative flocks.
“There is increasing interest in screening and determining flock status for diseases, including OPA.
“The nasal swab PCR is not yet commercially available. However, with additional funding and industry backing, we can look to determine how a robust and cost-effective assurance scheme for OPA can be developed to meet industry needs.”