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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 melanised focal changes. (A) Transverse section of necrotic muscle cells (asterisk) and severe fibrosis (arrow) with infiltrates of leukocytes. A cell-rich granuloma with melanin-containing cells is present in the right part of the picture (G), displaying a heterogeneous morphology (HE staining). (B) Severe vacuolisation and adipocytes with surrounding melano-macrophages (black) and clusters of regenerating myocytes with a basophilc cytoplasm (arrow) (HE staining). (C) Multiple vacuoles in an area with severe fibrosis (intense red staining) (van Gieson staining). (D) Several iron-containing macrophage-like cells (blue staining) in association with melano-macrophages (black) (Pearls’ Berlin blue staining). (A, C) scale bar = 100 μm, (B, D) scale bar = 50 μm.
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Fig4: Histological investigations of melanised focal changes. (A) Transverse section of necrotic muscle cells (asterisk) and severe fibrosis (arrow) with infiltrates of leukocytes. A cell-rich granuloma with melanin-containing cells is present in the right part of the picture (G), displaying a heterogeneous morphology (HE staining). (B) Severe vacuolisation and adipocytes with surrounding melano-macrophages (black) and clusters of regenerating myocytes with a basophilc cytoplasm (arrow) (HE staining). (C) Multiple vacuoles in an area with severe fibrosis (intense red staining) (van Gieson staining). (D) Several iron-containing macrophage-like cells (blue staining) in association with melano-macrophages (black) (Pearls’ Berlin blue staining). (A, C) scale bar = 100 μm, (B, D) scale bar = 50 μm.

Mentions: Melanised focal changes in individuals of Groups A-F were characterised by chronic degenerative inflammation with well-organised granulomas. This included central severe fibrosis, but also peripheral acute extensive tissue destruction and necrosis. Melano-macrophages were abundant throughout the granulomatous tissue and within well-organised granulomas (Figure 4A). Vacuoles were observed throughout the affected areas (Figure 4B). Signs of repair with extensive fibrosis and regeneration were detected in the chronically inflamed lesions (Figure 4C), confirming previous tissue destruction and subsequent repair. Haemorrhages were not observed. Macrophages with hemosiderin were detected in association with melano-macrophages, though only sparse amounts of positive cells were observed (Figure 4D). Group F contained one individual with a very faint pigmented spot, and examination of this sample showed muscle necrosis and some inflammatory infiltrates containing melano-macrophages.Figure 4


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 melanised focal changes. (A) Transverse section of necrotic muscle cells (asterisk) and severe fibrosis (arrow) with infiltrates of leukocytes. A cell-rich granuloma with melanin-containing cells is present in the right part of the picture (G), displaying a heterogeneous morphology (HE staining). (B) Severe vacuolisation and adipocytes with surrounding melano-macrophages (black) and clusters of regenerating myocytes with a basophilc cytoplasm (arrow) (HE staining). (C) Multiple vacuoles in an area with severe fibrosis (intense red staining) (van Gieson staining). (D) Several iron-containing macrophage-like cells (blue staining) in association with melano-macrophages (black) (Pearls’ Berlin blue staining). (A, C) scale bar = 100 μm, (B, 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

Fig4: Histological investigations of melanised focal changes. (A) Transverse section of necrotic muscle cells (asterisk) and severe fibrosis (arrow) with infiltrates of leukocytes. A cell-rich granuloma with melanin-containing cells is present in the right part of the picture (G), displaying a heterogeneous morphology (HE staining). (B) Severe vacuolisation and adipocytes with surrounding melano-macrophages (black) and clusters of regenerating myocytes with a basophilc cytoplasm (arrow) (HE staining). (C) Multiple vacuoles in an area with severe fibrosis (intense red staining) (van Gieson staining). (D) Several iron-containing macrophage-like cells (blue staining) in association with melano-macrophages (black) (Pearls’ Berlin blue staining). (A, C) scale bar = 100 μm, (B, D) scale bar = 50 μm.
Mentions: Melanised focal changes in individuals of Groups A-F were characterised by chronic degenerative inflammation with well-organised granulomas. This included central severe fibrosis, but also peripheral acute extensive tissue destruction and necrosis. Melano-macrophages were abundant throughout the granulomatous tissue and within well-organised granulomas (Figure 4A). Vacuoles were observed throughout the affected areas (Figure 4B). Signs of repair with extensive fibrosis and regeneration were detected in the chronically inflamed lesions (Figure 4C), confirming previous tissue destruction and subsequent repair. Haemorrhages were not observed. Macrophages with hemosiderin were detected in association with melano-macrophages, though only sparse amounts of positive cells were observed (Figure 4D). Group F contained one individual with a very faint pigmented spot, and examination of this sample showed muscle necrosis and some inflammatory infiltrates containing melano-macrophages.Figure 4

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