Sir, – In reply to Jim Walker’s Farmer's View in The SF, September 25, about OPA, I would agree with most of his comments.

If Jim could use his undoubted influence to encourage more funding and research towards finding a blood test or vaccine to fight this terrible disease, it would be a valuable service to the sheep industry.

He is wrong, however, to dismiss scanning as simply too late. As the disease is fatal, a positive blood test would also be too late.

Scanning can detect very small tumours with a great degree of accuracy, allowing sheep to be culled while they are still valuable, and reducing potential spread. It has clearly been demonstrated in many flocks that the number of clinical cases can be reduced rapidly over 3-4 years to well below 0.5%.

From an animal welfare point of view and also economically, scanning an infected flock can easily be justified.

As Jim is aware, no blood test is 100% accurate and no vaccine is 100% effective. While scanning may not be quite as sharp as we would like, it is currently the only tool in the box.

Purchasing breeding stock from a flock with a history of scanning, or scanning purchases at home, particularly rams, is currently the best safeguard against introducing infection.

Alastair MacArthur
Nunnerie, Elvanfoot, Biggar.