Proliferative Kidney Disease in Salmonids (PKD) – Gross Pathology

Rainbow trout with PKD. There is a marked hyperplasia of interstitium with the kidney thrown into bulbous ridges. The reddening is tge result of secondary yersinia infection.

Proliferative kidney disease (PKD) is an endoparasitic disease of salmonid fish caused by Tetracapsuloides bryosalmonae (Myxozoa: Malacosporea).  This chronic, largely renal interstitial disease is caused by the extraporogonic but intracellular stages of the parasite, which cause a severe granulomatous host response. The severity of the disease is linked to water temperature, with roughly 15 degrees °C as the cut-off: below that temperature, lesions and clinical disease are minimal. Above that temperature, however, lesions can be severe and mortality high. Inevitably, global warming has resulted in...


Figure 1. Multiple giant cells in the peritoneal cavity of salmon, a response to vaccine, its bright red character apparent (arrows). Similar to so-called Splendore-Hoeppli reactions (asteroid bodies).

Multinucleated cells, often simply called giant cells, are found in a variety of situations in teleost fish. They are not uncommon in granulomatous inflammatory responses, such as bacterial kidney disease, proliferative kidney disease, or as a response to vaccine, and are a result of fusion of macrophages or epithelioid cells. They are also found in virus infections, so-called syncytial giant cells, in which a number of non-macrophage cells, such as hepatocytes, fuse together. But giant cells are also found in normal fish as osteoclasts. Although...