Fig. 4

Comparative histopathology of PKD on rainbow trout during single and co-infection with WD. a Kidney section of single Tb infected group showing interstitial extrasporogonic stages of T. bryosalmonae surrounded by macrophage cells (rosette appearance, arrow) at 60 dpe. b Kidney section of single Tb infected group at 120 dpe, showing pronounced tubular regeneration and tubuloneogenesis with basophilic cytoplasm and increased numbers of mitotic figures (black arrow), note interstitial Tb stages (white arrow). c-e Mc-then Tb co-infected fish, 120 dpe to Mc (90 dpe to Tb), showing c expanded interstitium due to advanced fibrosis with infiltration of inflammatory cells (arrowhead), d higher magnification of (c) showing presence of mutinucleated giant cell (arrow) and the parasites (arrowheads) and e peritubular fibrosis (arrow). f Liver section of single Tb infected group at 120 dpe showing presence of inflammatory cellular aggregations containing few parasite stages (arrow). g Spleen of single Tb infected group at 120 dpe showing presence of T. bryosalmonae stages (arrow) in red and white pulp associated with inflammatory cellular infiltration around the zone of infection. H&E staining. Scale-bars: a, 50 μm; b, 100 μm; c, 50 μm; d, 20 μm; e, 50 μm; f, 50 μm; g, 20 μm