To scan or not to scan? The economics of transthoracic ultrasonography for ‘whole-flock’ ovine pulmonary adenocarcinoma screening in UK sheep flocks

Abstract

Background: Transthoracic ultrasonography (TTUS) is currently the only widely used method to diagnose suspected preclinical or subclinical cases of ovine pulmonary adenocarcinoma/Jaagsiekte (OPA) in live sheep. However, the economic impact of using TTUS as a screening test has not been described previously. Methods: Test characteristics for TTUS in a low-prevalence situation were obtained from a previous study of 1074 breeding ewes that underwent TTUS with an experienced operator. The economic impact was modelled using a 10,000-iteration partial budget simulation and probability sensitivity analysis to explore the relative influence of model variables. Results: In flocks of this size, culling true-positive and false-positive cases resulted in an estimated median net loss of £4647 (interquartile range: £3537–£6006), determined primarily by replacement ewe value and the cost of TTUS per ewe. Conclusion: The results of this study emphasise that great caution should be exercised by practitioners when determining if TTUS is appropriate as a screening test for OPA in low-prevalence flocks or subpopulations within a flock, such as younger age groups, where the losses incurred through the inadvertent culling of healthy sheep may significantly exceed any benefit derived from culling preclinical/subclinical cases.