Pathogenesis and clinical signs: The virus causes a proliferation of the alveolar lining cells which produce up to 500 ml fluid. The proliferative foci project into the alveolae and bronchi and then form slow-growing tumours with death at 3-4 years of age.

Low exercise tolerance, (hence the Afrikaans name of Jaagsiekte which means driving sickness), gradual weight loss, dyspnoea, and death.

Secondary bacterial infection by Pasteurella haemolytica often precipitates death.