common (Fig. 5.45). Nuclear enlargement is seen in some
fish which resemble Anitschkow myocytes which are
believed to be linked with myocardial repair. Within select
sections of liver, a mild, circumferential, subintimal fibrosis
of the central vein can be observed. HSMI and salmonid
pancreas disease (PD) are important differential diagnosis
and the potential overlap of more than one viral agent may
obscure the histopathological evaluation.
PMV belongs to the Totiviridae family and the virus
appears to be widespread in farmed fish. The recent identification of the causative virus will help in developing control
strategies.
5.11 Erythrocytic Inclusion Body Syndrome
Erythrocytic inclusion body syndrome (EIBS) is one of a
number of intraerythrocytic inclusion viruses which has
been reported from Atlantic, chum, Chinook, coho salmon
and rainbow trout, both from wild and farmed origin. Most
incidences are from sea water stock but also reported from
freshwater fish.
Affected fish may be lethargic with pale gills and pigmentation abnormalities. Internally, fish may show splenomegaly and evidence of a progressive anaemia, but in many
reports there is no specific correlation between infection and
clinical signs. Laboratory studies show a decreased
haematocrit. Each cycle of infection lasts around 45 days,
with higher water temperatures reported as the factor that
initiates infection, after which surviving fish appear to be
resistant to re-infection. Losses are generally low but fish
may become susceptible to secondary bacterial and
oomycete infections, with occurrence of indirect mortalities.
Histological assessment shows haemosiderin accumulation
within the splenic ellipsoidal sheaths and less frequently, the
kidney, although areas of haematopoietic necrosis are
reported. Similarly, there is a limited hepatocyte necrosis.
EIBS is recognised by the finding of round to ovoid,
randomly scattered, single or multiple basophilic bluish
Fig. 5.43 Longitudinal section showing early subendocardial infiltration of mononuclear cells in the spongy myocardium of farmed Atlantic
salmon with cardiomyopathy syndrome
Fig. 5.44 Thrombus in spongy myocardium in farmed Atlantic salmon
with cardiomyopathy syndrome. Medium power
Fig. 5.45 (a) Focal fibrinous epicarditis on the caudal face of the
ventricle of farmed Atlantic salmon broodstock. (b) Proliferative
epicarditis in farmed Atlantic salmon. Bar ¼200 μm
5.11 Erythrocytic Inclusion Body Syndrome
69
fish which resemble Anitschkow myocytes which are
believed to be linked with myocardial repair. Within select
sections of liver, a mild, circumferential, subintimal fibrosis
of the central vein can be observed. HSMI and salmonid
pancreas disease (PD) are important differential diagnosis
and the potential overlap of more than one viral agent may
obscure the histopathological evaluation.
PMV belongs to the Totiviridae family and the virus
appears to be widespread in farmed fish. The recent identification of the causative virus will help in developing control
strategies.
5.11 Erythrocytic Inclusion Body Syndrome
Erythrocytic inclusion body syndrome (EIBS) is one of a
number of intraerythrocytic inclusion viruses which has
been reported from Atlantic, chum, Chinook, coho salmon
and rainbow trout, both from wild and farmed origin. Most
incidences are from sea water stock but also reported from
freshwater fish.
Affected fish may be lethargic with pale gills and pigmentation abnormalities. Internally, fish may show splenomegaly and evidence of a progressive anaemia, but in many
reports there is no specific correlation between infection and
clinical signs. Laboratory studies show a decreased
haematocrit. Each cycle of infection lasts around 45 days,
with higher water temperatures reported as the factor that
initiates infection, after which surviving fish appear to be
resistant to re-infection. Losses are generally low but fish
may become susceptible to secondary bacterial and
oomycete infections, with occurrence of indirect mortalities.
Histological assessment shows haemosiderin accumulation
within the splenic ellipsoidal sheaths and less frequently, the
kidney, although areas of haematopoietic necrosis are
reported. Similarly, there is a limited hepatocyte necrosis.
EIBS is recognised by the finding of round to ovoid,
randomly scattered, single or multiple basophilic bluish
Fig. 5.43 Longitudinal section showing early subendocardial infiltration of mononuclear cells in the spongy myocardium of farmed Atlantic
salmon with cardiomyopathy syndrome
Fig. 5.44 Thrombus in spongy myocardium in farmed Atlantic salmon
with cardiomyopathy syndrome. Medium power
Fig. 5.45 (a) Focal fibrinous epicarditis on the caudal face of the
ventricle of farmed Atlantic salmon broodstock. (b) Proliferative
epicarditis in farmed Atlantic salmon. Bar ¼200 μm
5.11 Erythrocytic Inclusion Body Syndrome
69