Viral Hemorrhagic septicemia
A) Rhabdovirus
B) Widespread and very contagious viral disease of rainbow trout. This is a serious disease of trout in Europe. Affects both Salmonid in fresh water and sea water. Disease occurs in temperatures below 14oC.
C) Two forms of the Disease - Acute and Chronic
1) Acute disease: High mortality in affected fish. Fish have pale gills, dark body coloration, ascites, exophthalmus and erratic swimming behavior (spiraling). Hemorrhage is common in the eyes, skin, serosal surfaces of the intestines and muscles. Necrosis of the hematopoietic and lymphoid elements of the anterior kidney and congestion and necrosis of the hepatic parenchyma are histopathologic findings.
2) Chronic disease: See a slower prolonged mortality. Fish become lethargic, have pale anemic gills, darken skin coloration, exophthalmus, and distention of the abdominal cavity. Internal organs are commonly involved with splenomegaly, hepatomegaly, and swollen kidneys.
D) Turbot, sea bass, and Atlantic salmon are commonly affected by similar viruses.
E) Transmission is believed to be direct with contact of carriers and contaminated water and feed. Vertical transmission via the egg is not reported.