Histopathological findings in harbour seals (Phoca vitulina) found dead on the German North sea coast

Various organs--lung, trachea, liver, kidney, heart, adrenal gland, skin, spleen, thymus, lymph node, gut, thyroid, spinal cord and brain--were removed from 43 seals at dissections performed on the German North sea coast. The specimens were fixed in formalin and routinely processed for light microscopy. The major pathological findings were Lung: acute congestion with interstitial and intra-alveolar oedema; intra-alveolar haemorrhage; suppurative bronchitis and bronchopneumonia; larvae and adult forms of Parafilaroides gymnurus. Liver: acute congestion; granulomatous lesions and infiltrates of eosinophils; intravascular nematodes. Spleen: varying degrees of atrophy of the white pulp; haemosiderosis; acute congestion of the red pulp. Lymph nodes: varying degrees of atrophy of the lymphatic tissue; long-standing sinus histiocytosis with partial fibrotic obliteration of the lumina; parasitic infiltration, sometimes with the Splendore-Hoeppli phenomenon; germinal centre hyperplasia. Thymus: pronounced atrophy of the lymphatic tissue, particularly in the cortical areas. Thyroid: marked reduction in colloid content. The other organs studied were normal or showed only minor histopathological changes. The morphological findings do not allow definite conclusions to be made about the aetiology and pathogenesis of the illness and death of the seals. However, evidence has been published that the seals' illness is probably due to canine distemper virus. The atrophy of the lymphoreticular tissues is consistent with infection by this virus.