Ovine pulmonary adenocarcinoma (OPA), also known as Jaagsiekte, is a contagious lung tumour of sheep caused by a retrovirus, leading to progressive respiratory failure and significant welfare consequences.
OPA progresses silently over months before clinical signs appear, meaning affected sheep experience a prolonged period of compromised respiratory function that may go undetected. In advanced disease, the effort of breathing becomes severe, and animals lose body condition rapidly as the energetic cost of laboured respiration increases. The accumulation of fluid in the airways causes genuine respiratory distress. Because there is no treatment, early identification and humane culling of affected individuals is the primary welfare intervention. Closed-flock policies and biosecurity measures to prevent introduction of the virus protect future generations of animals from this difficult disease.