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Piscine orthoreovirus (PRV) in red and melanised foci in white muscle of Atlantic salmon (Salmo salar).

Bjørgen H, Wessel Ø, Fjelldal PG, Hansen T, Sveier H, Sæbø HR, Enger KB, Monsen E, Kvellestad A, Rimstad E, Koppang EO - Vet. Res. (2015)

Bottom Line: Red focal changes contained significantly higher levels of PRV RNA than apparently non-affected areas in white muscle of the same individuals.Some changes displayed a transient form between a red and melanised pathotype, indicating a progression from an acute to a chronic manifestation.We conclude that PRV is associated with the focal pathological changes in the white muscle of farmed Atlantic salmon and is a premise for the development of focal melanised changes.

View Article: PubMed Central - PubMed

Affiliation: Institute of Basic Science and Aquatic Medicine, School of Veterinary Medicine, Norwegian University of Life Sciences, Oslo, Norway. havard.bjorgen@nmbu.no.

ABSTRACT
Melanised focal changes (black spots) are common findings in the white skeletal muscle of seawater-farmed Atlantic salmon (Salmo salar). Fillets with melanised focal changes are considered as lower quality and cause large economic losses. It has been suggested that red focal changes (red spots) precede the melanised focal changes. In the present work, we examined different populations of captive and wild salmon for the occurrence of both types of changes, which were investigated for the presence of different viruses by immunohistochemistry and RT-qPCR. The occurrence of red or melanised foci varied significantly between the populations, from none in wild fish control group, low prevalence of small foci in fish kept in in-house tanks, to high prevalence of large foci in farm-raised salmon. Large amounts of Piscine orthoreovirus (PRV) antigen were detected in all foci. No other viruses were detected. Red focal changes contained significantly higher levels of PRV RNA than apparently non-affected areas in white muscle of the same individuals. Some changes displayed a transient form between a red and melanised pathotype, indicating a progression from an acute to a chronic manifestation. We conclude that PRV is associated with the focal pathological changes in the white muscle of farmed Atlantic salmon and is a premise for the development of focal melanised changes.

No MeSH data available.


Related in: MedlinePlus

Histological investigations of red focal changes. (A) Necrotic myocytes display pale cytoplasm and appear homogenous without striations (arrow). Myocyte with striations (asterisk) (HE staining). (B) Necrotic myocytes with erythrocytes apparently located within the myocytes (arrowheads) and some infiltrations of macrophage-like cells (arrow) (HE staining). (C) Centrally located vacuoles of varying size, surrounded by moderate levels of collagen (intense red) and modest numbers of leukocytes (van Gieson staining). (D) Focal haemorrhage surrounding vacuoles. The edges of the vacuoles are positive for ferric iron (blue colour) (Perls’ Berlin blue staining). (A, C) scale bar = 200 μm, (B) scale bar = 100 μm, (D) scale bar = 50 μm.
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Fig3: Histological investigations of red focal changes. (A) Necrotic myocytes display pale cytoplasm and appear homogenous without striations (arrow). Myocyte with striations (asterisk) (HE staining). (B) Necrotic myocytes with erythrocytes apparently located within the myocytes (arrowheads) and some infiltrations of macrophage-like cells (arrow) (HE staining). (C) Centrally located vacuoles of varying size, surrounded by moderate levels of collagen (intense red) and modest numbers of leukocytes (van Gieson staining). (D) Focal haemorrhage surrounding vacuoles. The edges of the vacuoles are positive for ferric iron (blue colour) (Perls’ Berlin blue staining). (A, C) scale bar = 200 μm, (B) scale bar = 100 μm, (D) scale bar = 50 μm.

Mentions: Red focal changes in individuals of Groups A, C and E were all characterised by an acute haemorrhagic necrotic myositis. In more detail, we observed severely disorganised architecture of tissues including several myocytes with a complete loss of striation conformal with coagulation necrosis (Figure 3A). Organisation into granulomas was not observed. Poikilocytosis was highly prevalent, as both elongated and rounded erythrocytes were present. Focal areas of haemorrhage and accumulation of extravasal erythrocytes were present in all red changes accompanied by coagulation necrosis of myocytes. Erythrocytes and macrophage-like cells were observed both between and within necrotic myocytes (Figure 3B). In some changes, myocytes adjacent to the affected site showed signs of regeneration displaying a basophilic appearance and a central rowing of nuclei. Occasional melano-macrophages were detected. Fibrosis was present to some degree, mainly associated with vacuoles that varied in size and shape (Figure 3C). Staining with Perls’ Berlin blue technique confirmed the presence of haemosiderin in the periphery of the vacuoles, especially in association with large infiltrates of erythrocytes (Figure 3D).Figure 3


Piscine orthoreovirus (PRV) in red and melanised foci in white muscle of Atlantic salmon (Salmo salar).

Bjørgen H, Wessel Ø, Fjelldal PG, Hansen T, Sveier H, Sæbø HR, Enger KB, Monsen E, Kvellestad A, Rimstad E, Koppang EO - Vet. Res. (2015)

Histological investigations of red focal changes. (A) Necrotic myocytes display pale cytoplasm and appear homogenous without striations (arrow). Myocyte with striations (asterisk) (HE staining). (B) Necrotic myocytes with erythrocytes apparently located within the myocytes (arrowheads) and some infiltrations of macrophage-like cells (arrow) (HE staining). (C) Centrally located vacuoles of varying size, surrounded by moderate levels of collagen (intense red) and modest numbers of leukocytes (van Gieson staining). (D) Focal haemorrhage surrounding vacuoles. The edges of the vacuoles are positive for ferric iron (blue colour) (Perls’ Berlin blue staining). (A, C) scale bar = 200 μm, (B) scale bar = 100 μm, (D) scale bar = 50 μm.
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC4562189&req=5

Fig3: Histological investigations of red focal changes. (A) Necrotic myocytes display pale cytoplasm and appear homogenous without striations (arrow). Myocyte with striations (asterisk) (HE staining). (B) Necrotic myocytes with erythrocytes apparently located within the myocytes (arrowheads) and some infiltrations of macrophage-like cells (arrow) (HE staining). (C) Centrally located vacuoles of varying size, surrounded by moderate levels of collagen (intense red) and modest numbers of leukocytes (van Gieson staining). (D) Focal haemorrhage surrounding vacuoles. The edges of the vacuoles are positive for ferric iron (blue colour) (Perls’ Berlin blue staining). (A, C) scale bar = 200 μm, (B) scale bar = 100 μm, (D) scale bar = 50 μm.
Mentions: Red focal changes in individuals of Groups A, C and E were all characterised by an acute haemorrhagic necrotic myositis. In more detail, we observed severely disorganised architecture of tissues including several myocytes with a complete loss of striation conformal with coagulation necrosis (Figure 3A). Organisation into granulomas was not observed. Poikilocytosis was highly prevalent, as both elongated and rounded erythrocytes were present. Focal areas of haemorrhage and accumulation of extravasal erythrocytes were present in all red changes accompanied by coagulation necrosis of myocytes. Erythrocytes and macrophage-like cells were observed both between and within necrotic myocytes (Figure 3B). In some changes, myocytes adjacent to the affected site showed signs of regeneration displaying a basophilic appearance and a central rowing of nuclei. Occasional melano-macrophages were detected. Fibrosis was present to some degree, mainly associated with vacuoles that varied in size and shape (Figure 3C). Staining with Perls’ Berlin blue technique confirmed the presence of haemosiderin in the periphery of the vacuoles, especially in association with large infiltrates of erythrocytes (Figure 3D).Figure 3

Bottom Line: Red focal changes contained significantly higher levels of PRV RNA than apparently non-affected areas in white muscle of the same individuals.Some changes displayed a transient form between a red and melanised pathotype, indicating a progression from an acute to a chronic manifestation.We conclude that PRV is associated with the focal pathological changes in the white muscle of farmed Atlantic salmon and is a premise for the development of focal melanised changes.

View Article: PubMed Central - PubMed

Affiliation: Institute of Basic Science and Aquatic Medicine, School of Veterinary Medicine, Norwegian University of Life Sciences, Oslo, Norway. havard.bjorgen@nmbu.no.

ABSTRACT
Melanised focal changes (black spots) are common findings in the white skeletal muscle of seawater-farmed Atlantic salmon (Salmo salar). Fillets with melanised focal changes are considered as lower quality and cause large economic losses. It has been suggested that red focal changes (red spots) precede the melanised focal changes. In the present work, we examined different populations of captive and wild salmon for the occurrence of both types of changes, which were investigated for the presence of different viruses by immunohistochemistry and RT-qPCR. The occurrence of red or melanised foci varied significantly between the populations, from none in wild fish control group, low prevalence of small foci in fish kept in in-house tanks, to high prevalence of large foci in farm-raised salmon. Large amounts of Piscine orthoreovirus (PRV) antigen were detected in all foci. No other viruses were detected. Red focal changes contained significantly higher levels of PRV RNA than apparently non-affected areas in white muscle of the same individuals. Some changes displayed a transient form between a red and melanised pathotype, indicating a progression from an acute to a chronic manifestation. We conclude that PRV is associated with the focal pathological changes in the white muscle of farmed Atlantic salmon and is a premise for the development of focal melanised changes.

No MeSH data available.


Related in: MedlinePlus