Disseminated Intravascular Coagulation in “Hitra Disease” (Hemorrhagic Syndrome) in Farmed Atlantic Salmon

Necropsy findings in adult salmon with subclinical “Hitra disease” (hemorrhagic syndrome) varied from negligible to hemorrhagic diathesis with generalized edema. By light microscopy, minute vessels were dilated, arterioles had mural necrosis, and thrombi were present. Occlusions consisted of fused erythrocytes and fibrin. Ultrastructurally, endothelial nuclei were pyknotic with condensed chromatin. The cytoplasm contained numerous laminar structures and electron-dense particles. Damaged erythrocytes adhered to the degenerated endothelium, and coalesced erythrocytes had formed mural thrombi or filled the vascular lumen. Microthrombi were frequently seen. There were no thrombocytes in the thrombi, which consisted of erythrocytes or reticulocytes. Clinically healthy farmed salmon parr showed the same disorders as did adults, but to a far lesser degree. Wild salmon parr had normal microvasculature. Results indicate that disseminated intravascular coagulation (DIC) occurs in “Hitra disease” in farmed Atlantic salmon.