Cerebral segmental polyarteritis of unknown aetiology in sheep.

Vasculitis affecting the meningeal elastic arteries was identified in six sheep of various breeds during routine diagnostic investigation. The lesions consisted of multifocal intimal proliferation, thickening of the tunica media, multifocal infiltration of the media by inflammatory cells and more extensive perivascular accumulation of lymphocytes and plasma cells within the tunica adventitia. Fibrinoid necrosis affected an intergyral artery in one sheep. Immunohistochemistry failed to demonstrate pestivirus antigen associated with the lesions and no alternative aetiology was defined. Possible causes of meningeal segmental polyarteritis in sheep are discussed.