Ovine pulmonary adenocarcinoma (OPA), or Jaagsiekte as it is often commonly known, is a relatively new disease in terms of industry awareness. The disease, which results from the Jaagsiekte sheep retrovirus (RSV), is transmitted from sheep to sheep mainly through the respiratory system and causes a lung tumour likened to cancer that will eventually be fatal.

The reason it is described as a relatively new disease for the sheep industry is that it is challenging to identify and, as such, has not been suspected or identified in cases of mortality it is likely to have been the cause of.

The lack of a reliable diagnostic blood test has been a major barrier in establishing prevalence levels, with sheep only really identified where they were submitted for a post-mortem examination.

It is only in recent years that there has been a greater appreciation of the threat of OPA and the devastating consequences it can have for some flocks. The increased awareness has stemmed primarily from research carried out by the Moredun Research Institute, Penicuik, Scotland.

The institute has been actively involved in developing and fine-tuning trans-thoracic ultrasonography as the best available method of detection for OPA lesions in live sheep, before the development of clinical signs.

In recent years, the institute has held courses and workshops to provide advanced clinical training for established vets and those studying veterinary.

Northern Ireland

The disease has only really come into the public eye in Ireland and Northern Ireland in recent years. At the 2018 Teagasc sheep conference, Dr Jason Barley of the Agri Food and Bioscience Institute (AFBI) and Patrick Grant, The Sheep Vet, delivered a paper giving an overview of the disease from a veterinary and diagnostic perspective.

Barley and Grant have been working closely together in recent years, testing the accuracy of ultrasound scanning as a means of identifying the disease at an early stage in an animal’s life in order to prevent the spread and allow flocks to salvage a value from animals when they are in relatively good health and body condition.

The AFBI and CAFRE have also been working closely together on implementing a flock control programme in the flock run at their Hill Farm Development Centre in Glenwherry, Co Antrim.

In the last two years, there has been an increase in the number of veterinary practices in Northern Ireland now offering an OPA diagnostic service, with a handful of practitioners receiving training in this area.

The increase is farmer-driven, with the number of farmers taking an interest in the disease slowly starting to rise. This was reflected in the large attendance at an information evening held on Hill Farm in 2019.

The Northern Ireland Sheep Programme has identified OPA as an important area that the programme can hopefully help to shed more light on in future.

Industry challenge

Progress in this area at industry level is likely to be a slow burner given diagnostic challenges, but this should not in any way detract from the importance of farmers investigating potential issues and putting a flock health programme in place.

The greatest prevalence of the disease to date has been identified in hill flocks, but it is also prevalent in lowland flocks. The fact that hill flocks are often under more pressure could be a factor in explaining why it seems to appear most here.

The experience of the CAFRE flock at Glenwherry shows that improvements can be made in this area. Table 1 details the results from the last four scannings. There has been a major improvement across the three metrics used for classifying sheep, as explained on page 40.

The future target for the flock is to scan periodically to ensure the incidence of disease is kept low, while attention will also be given to replacement sheep coming on to the farm and their farm of origin, as well as getting a good assessment of their health, in terms of OPA status.