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...
![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.](https://sp-ao.shortpixel.ai/client/to_webp,q_glossy,ret_img,w_600,h_361/https://fishhistopathology.com/wp-content/uploads/2019/05/feature-image-2.jpg)