Recent research by Moredun scientists and colleagues has provided new opportunities for the development of diagnostic tests for ovine pulmonary adenocarcinoma (OPA). OPA is a contagious respiratory disease of sheep that causes significant economic losses and animal welfare problems for affected flocks.
Moredun’s OPA research is predominantly aimed at developing tests to diagnose early OPA in order to enable test-and-cull in affected flocks, to provide assurance that sheep to be purchased do not carry the disease and eventually to eradicate OPA. The past year has seen progress in three main areas as our research team continues to strive towards combatting this infectious and fatal lung disease of sheep.
i) One project is using cutting edge technology to identify potential biomarkers of OPA in the blood of infected animals. We have examined gene activation in OPA tumours and found a number of cancer-associated markers are produced in increased amounts. The next stage will evaluate their potential usefulness for diagnosing OPA. While this work is at an early stage, we hope that it will result in a lab test for diagnosing OPA in individual animals in the early stages.
ii) A diagnostic assay based on nasal swab sampling of thin, cull ewes has been developed in a pilot study with Biobest Laboratories Ltd. This test shows good potential as a flock test and would be particularly useful as part of a flock health assurance scheme where annual testing was undertaken to provide information on health status which could be used to inform management decisions to improve flock performance and would allow buyers to purchase low risk animals. Further validation work is planned.
iii) Transthoracic ultrasound scanning is very useful to confirm a diagnosis of OPA in individual sheep or for screening bought-in or for sale animals, even though it cannot guarantee that a sheep is free of OPA because it cannot detect the very smallest tumours. In the past year whole flock screening of known OPA-affected flocks with Dr Phil Scott (Capital Veterinary Services) has found that on average 1-2% of sheep have OPA without clinical signs at the time of scanning. Older and thinner sheep were more likely to be positive but we also found OPA in gimmers and shearlings and in sheep with good condition scores. Generally the sensitivity and specificity of scanning for OPA is very good. Occasionally lung consolidation from bacterial or parasitic infection gives a false positive scan but the veterinary advice would be that if there are very large lung lesions, such as abscesses, to cull anyway as these sheep will never do well. Very small lesions found by ultrasound could also be false positives therefore the best course of action is to quarantine and re-scan in 3-6 months. Whole flock scanning enables OPA-affected sheep to be selected for culling at a time when they are still in good condition and of some value, avoiding later knackery uplift costs, and should also reduce spread of the virus within the flock. Scanning is also useful to identify thin sheep that don’t have OPA so that other health issues may be addressed. The effectiveness of using ultrasound scanning as a basis for a test-and-cull policy will be determined over the next few years.
Funding for the above projects came from i) the Biotechnology and Biological Sciences Research Council (BBSRC) and the Rural & Environment Science & Analytical Services Division of the Scottish Government (RESAS) ii) The Agriculture and Horticulture Development Board, Hybu Cig Cymru (Meat Promotion Wales), Northern Ireland Agricultural Research and Development Council (AgriSearch) and Biobest Laboratories Ltd, with some support from the Animal and Plant Health Agency.iii) RESAS. Additional data was obtained from scanning time donated by Dr Phil Scott or paid for by individual farmers.