Bluetongue is a devastating viral disease in sheep transmitted by midges, causing severe inflammation, lameness, and high mortality with significant animal welfare implications for affected flocks.
Bluetongue disease causes profound suffering in affected sheep. The acute phase involves high fever (over 40 degrees Celsius), severe inflammation of the oral mucosa causing painful ulcers and difficulty eating or drinking, and lameness so severe that animals cannot walk to water or food. The swollen, blue tongue that characterises severe cases reflects oxygen deprivation from respiratory compromise. Animals in acute disease show visible pain behaviours including teeth grinding, vocalisation, and prostration. Recovery, when it occurs, is prolonged and leaves animals debilitated for weeks with permanent damage to hoof horn, muscle, and respiratory function. Outbreaks in naive flocks — such as the northern European outbreaks following emergence of serotype 8 in 2006 and more recently serotype 3 — resulted in the deaths of millions of sheep. Preventive vaccination of susceptible flocks in at-risk areas is both welfare-protective and economically rational. Culling severely affected animals that cannot eat, drink, or walk is a humane endpoint decision that prevents prolonged suffering.