Histopathology of Chronic Liver Disease in Atlantic Salmon Raised in Nootka Sound in 2014.

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Willa Mitchell
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1 Histopathology of Chronic Liver Disease in Atlantic Salmon Raised in Nootka Sound in Hein Snyman BVSc, DVSc, Dip. ACVP Animal Health Centre - BC Ministry of Agriculture Net Pen Liver Disease Workshop Campbell River, BC - May 29, 2015

2 Introduction Normal structure & function Case description Lesion discussion Additional investigation Conclusions

3 The Fish Liver Cranial coelomic cavity Grossly not lobed Sinusoidal structure Double cell layer with interspersed

4 Blood Supply In Hepatic artery Portal vein Out Hepatic vein biomedical.materialise.com

5 Histological structure Classic hepatic lobule not as apparent in fish Function units still present

6 Nutrient metabolism Digestion (bile) Protein synthesis Functions Detoxification and excretion - Biotransformation (phase I and II, cytochrome P450 enzymes)

7 Case Description July 2 nd 2014 Site A West coast of Vancouver Island - Nootka Sound Low mortality (~1%) Preharvest population Multiple organs/tissues from 5 recently dead fish

8 Case Description Site A Characteristic histological lesions 4/5 NPLD; 1/5 early NPLD Shortly thereafter July 7, 2014 Site B 5/5 fish with NPLD

9 Initial Interpretation NPLD lesions were not unusual But clinical presentation did not fit pre-harvest fish greater population effect suppressed feeding halalfocus.net

10 Living Population July 8, 2014 Multiple organs from 5 fish from the living population

11 Living Population July 8, 2014 Multiple organs from 5 fish from the living population 1/5 with early NPLD 4/5 with mild evidence of low-grade hepatotoxicity

14 Pigmented Macrophage Aggregates Normal structures common in the liver, spleen, and kidney of most fish species. Lipofuscin & hemosiderin Cell breakdown products Volume with age Increased hepatocellular turnover. Chronic marker (PMP)

20 Hepatocellular Megalocytosis and Evidence of sublethally injured cells Affected cells might be able to survive for several months. Chronic marker Several types of toxins: aflatoxins pyrrolizidine alkaloids complex chemical mixtures from marine sediment extracts algal toxin microcystin-lr Karyomegaly (MEG)

21 Normal BPEC

23 Biliary Preductular Cell Hyperplasia (BPH) Cellular regeneration Evidence of exposure to toxins Chronic marker

24 Perivascular and Pericholangiolar Inflammation (PVL & CPL) Leukocytic inflammation around blood vessels and bile ductules Non-sepcific Antigenic stimulation Chronic marker

25 Normal Bile Duct Pericholangiolar Inflammation (CPL)

26 Normal Venule Perivascular Inflammation (PVL)

29 Hepatocellular Hydropic Degeneration Reversible change resulting from acute cellular damage hours Organelle swelling Acute marker ongoing injury When no longer reversible single cell necrosis (SCN).

34 Diagnosis Lesions essentially consistent with: Netpen Liver Disease (NPLD) Evidence of chronic disease But also acute and ongoing injury

35 Disease Progression Three additional sequential samples Site B 16 & 28 July & 20 August (Harvest) 20 livers each None (0) Mild (1) Moderate (2) Severe (3) Average lesions score

36 3.5 Site B PMP MEG BPH Jul 8 Jul 16 Jul 28 Jul 20 Aug

37 Site B CPL PVL Jul 8 Jul 16 Jul 28 Jul 20 Aug

38 1.2 Site B HHD SCN Jul 8 Jul 16 Jul 28 Jul 20 Aug

39 Disease Progression Site A 8 & 20 August livers each None (0) Mild (1) Moderate (2) Severe (3) Average lesions score

40 3 Site A PMP MEG BPH Jul 8 Aug 20 Aug

41 3 Site A CPL PVL Jul 8 Aug 20 Aug

42 1.2 Site A HHD SCN Jul 8 Aug 20 Aug

43 History Repeats Itself In November a similar situation occurred in two additional sites (sites C & D) Site C Nov 3 rd - 3/5 fish with NPLD Site D Nov 7 th - 4/5 fish with NPLD

44 Site C Pen prevalence November 24 th and December 8 th fish/pen 6 pens 120 livers

45 2.5 Site C PMP MEG BPH Pen 1 Pen 2 Pen 3 Pen 4 Pen 5 Pen 6

46 1.2 Site C CPL PVL Pen 1 Pen 2 Pen 3 Pen 4 Pen 5 Pen 6

47 Site C HHD SCN Pen 1 Pen 2 Pen 3 Pen 4 Pen 5 Pen 6

48 Site D December 8 th 2014 (Harvest) 20 fish/pen 4 pens 80 livers

49 Site D PMP MEG BPH Pen 1 Pen 2 Pen 3 Pen 4

50 0.8 Site D CPL PVL Pen 1 Pen 2 Pen 3 Pen 4

51 1.4 Site D HHD SCN Pen 1 Pen 2 Pen 3 Pen 4

52 Conclusions Chronic liver disease (NPLD) Increase in severity over time Evidence of ongoing hepatocellular injury Ongoing low grade exposure to an environmental hepato-toxin (microcystin?) Route of exposure? Failure to excrete endogenous circulating toxins due to aberrant liver function

53 Thank You

55 Hepatocellular Hydropic Degeneration

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