Table 5 Furunculosis—microscopic pathology Clinical course of disease Microscopic Peracute Acute Subacute signs infection infection infection Bacterial Small Seen Conspicuous colonisation colonies in: anywhere, infection, especially: especially: branchial mesenchyme heart heart (myocardial (myocardial myocardium degeneration) degeneration; fibrinoid anterior kidney kidney degeneration) (possible macrophage spleen spleen involvement; (vascular renal tubular collapse, degeneration) splenomegaly ) spleen (vascular collapse, splenomegaly) gills (lamellar thrombosis) skin (subdermal colonies) Inflammatory No Yes Yes infiltrate Necrosis Limited Toxic Only heart haematopoetic and spleen necrosis Ellipsoidal necrosis (spleen) Laboratory tests Specimens required Confirmation of diagnosis can be made by culture and identification of A. salmonicida subsp. salmonicida from infected fish. Moribund, clinically affected fish that have been euthanased
Table 5 Furunculosis—microscopic pathology Microscopic signs Clinical course of disease Peracute infection Acute infection Subacute infection Bacterial colonisation Small colonies in: branchial mesenchyme myocardium anterior kidney spleen Seen anywhere, especially: heart (myocardial degeneration) kidney (possible macrophage involvement; renal tubular degeneration) spleen (vascular collapse, splenomegaly) gills (lamellar thrombosis) skin (subdermal colonies) Conspicuous infection, especially: heart (myocardial degeneration; fibrinoid degeneration) spleen (vascular collapse, splenomegaly ) Inflammatory infiltrate No Yes Yes Necrosis Limited Toxic haematopoetic necrosis Ellipsoidal necrosis (spleen) Only heart and spleen Laboratory tests Specimens required Confirmation of diagnosis can be made by culture and identification of A. salmonicida subsp. salmonicida from infected fish. Moribund, clinically affected fish that have been euthanased