Pathogenesis:
- Infection of the lymphoid tissue of the nasopharynx then a leucopaenia and immunosuppresion.. Pathognomic medial necrosis of arteries. This lesion is responsible for oedema, haemorrhage and more rarely, thrombosis and infarction. Conjunctivitis and palpebral oedema give the name 'pink eye'. Oedema is also seen in the legs and lower abdomen.
- Thoroughbred stallions have been shown to be intermittent or persistent shedders of virus, with the accessory sex glands (prostate and seminal vesicles) being the sites of persistence.
- Virus infects the respiratory and alimentary tract resulting in nasal catarrh, coughing, dyspnoea (pleurisy), diarrhoea and colic.
- Abortions occur 10-30 days after infection in 50% of pregnant mares. Congenital infection can also occur.