A DISEASE 'iceberg' is threatening the Scottish sheep sector – the fatal and infectious lung condition ovine pulmonary adenocarcinoma, traditionally known as Jaagsiekte.

Caused by a virus which infects cells in the lung leading to tumours, Jaagsiekte has been recognised by generations of flock managers as a cause of sheep losses, manifesting itself in its later stages by the accumulation of fluid within the affected animal's lungs, effectively causing them to drown.

However surveys at sheep abattoirs and of fallen stock have demonstrated that the reach and severity of OPA is increasing, and according to Livestock Health Scotland, the disease is now being diagnosed in all regions of Scotland and is probably impacting on all breeds.

As reported in last weeks' The Scottish Farmer, in the absence of an accurate laboratory test for the disease, the Moredun Research Institute has taken to scanning sheep's lungs to identify OPA tumours at an early stage. The call now is for sheep breeders to use this technique and make a start on weeding the infection out of their flocks.

National Sheep Association regional development officer George Milne said that it was an issue that they were keenly aware of: "The jist of it is that Jaagsiekte does seem to be an ongoing, rising problem. It's been a subject of discussion several times at UK Livestock Scotland when we've been looking at disease issues that need tackled, but the problem is that it is far from a straightforward disease to deal with.

"The Moredun are actively doing work to fight the problem, including diagnostic scanning, and other means of identifying Jaagsiekte in sheep. It is very much a problem that is on our radar though, and we are doing what we can to try and figure out the best way to move forward. It's our priority to see progression on the issue."

With the support of those experts from Moredun, SAC and sheep veterinarians, LHS and NFU Scotland this week produced a brief guide to OPA, its role in different flocks and the need for sheep keepers to discuss an OPA strategy with their vets.

LHS chairman Nigel Miller, former NFUS president and a qualified vet, said: “Like other 'iceberg' diseases, OPA can establish unseen within a flock until infection rates rise and start to erode performance and trigger increased mortality.

“With no specific laboratory screening available, control is a real challenge and intervention is crucial at two levels. In OPA affected flocks, action is needed to reduce infection rates, and in those flocks unaffected by OPA, you must seek to maintain disease freedom," he advised.

“The introduction of ultrasound lung scanning provides a much-needed diagnostic tool. Through the identification of early lung lesions, scanning can pinpoint risk animals before clinical disease is apparent. Lung scanning has a role in a test and cull programme in OPA affected flocks but may also be used to screen purchased breeding stock to reduce the risk of introducing disease into clear flocks," explained Mr Miller.

NFUS animal health policy manager Penny Middleton added: “OPA has been cropping up more and more as a priority disease which producers are very concerned about. The focus has mostly been from flock owners concerned about buying in the disease, knowing that control can be difficult.

“Lung scanning, whilst it has limits, is a useful tool to help buyers reduce their risk of introducing OPA into a clean flock, as well as offering affected flocks the option of scanning the flock and removing infected sheep whilst they still have some value and reducing the exposure of other sheep in the flock," she said.

“Industry needs to start asking for this service and encouraging vets to undergo the training to be able to offer this service more widely.”