Polyarteritis nodosa associated with nosematosis in blue foxes.

The patho-morphological lesions in fox nosematosis (encephalitozoonosis) were studied in a material comprising 150 young blue foxes from 23 different farms. Disseminated nosematosis in blue fox pups was regularly accompanied by severe vasculitis, affecting medium-sized and small arteries in various organs. The acute damage has the form of a necrotizing angiitis, with mural necrosis and sometimes resultant thrombosis. The causative organism Nosema cuniculi, is frequently present in the freshly affected arterial walls, either in endothelial or in medial smooth muscle cells. Older lesions include nodular fibrous thickening of the arterial walls, and intimal proliferation, sometimes with luminal obliteration. The conclusion is drawn that the arterial lesions are morphologically equivalent to classical polyarteritis nodosa.