Proliferative kidney disease in rainbow trout: time- and temperature-related renal pathology and parasite distribution

Abstract

Proliferative kidney disease is a parasitic infection of salmonid fishes caused by Tetracapsuloides bryosalmonae. The main target organ of the parasite in the fish is the kidney. To investigate the influence of water temperature on the disease in fish, rainbow trout Oncorhynchus mykiss infected with T bryosalmonae were kept at 12 degrees C and 18 degrees C. The number of parasites, the type and degree of lesions in the kidney and the mortality rate was evaluated from infection until full development of disease. While mortality stayed low at 12 degrees C, it reached 77% at 18 degrees C. At 12 degrees C, pathological lesions were dominated by a multifocal proliferative and granulomatous interstitial nephritis. This was accompanied by low numbers of T. bryosalmonae, mainly located in the interstitial lesions. With progression of the disease, small numbers of parasites appeared in the excretory tubuli, and parasite DNA was detected in the urine. Parasite degeneration in the interstitium was observed at late stages of the disease. At 18 degrees C, pathological lesions in kidneys were more severe and more widely distributed, and accompanied by significantly higher parasite numbers. Distribution of parasites in the renal compartments, onset of parasite degeneration and time course of appearance of parasite DNA in urine were not clearly different from the 12 degrees C group. These findings indicate that higher mortality at 18 degrees C compared to 12 degrees C is associated with an enhanced severity of renal pathology and increased parasite numbers.

Complex interaction between proliferative kidney disease, water temperature and concurrent nematode infection in brown trout

“…In a recent experimental study dealing with rainbow trout, we showed that as soon as 103 d post-infection no T. bryosalmonae were visible by IHC, independent of water temperature (Schmidt-Posthaus et al 2012). However, translocation into the tubular lumen was not obvious in the latter study, as elimination of T. bryo salmonae seemed rather to be taking place through degeneration of the parasites in the interstitium than by translocation into the tubular lumen (Bettge et al 2009, Schmidt-Posthaus et al 2012. These species differences were also shown by Morris & Adams (2006) and Grabner & El-Matbouli (2008), who were only able to demonstrate excreted spores in brown Salmo trutta and brook trout Salvelinus fontinalis, but not in rainbow trout.…”

“…The spread and consequences of the disease are suspected to be enhanced by water temperature (Wahli et al 2008, Bettge et al 2009, Okamura et al 2011). The disease is caused by Tetracapsuloides bryosalmonae (Myxozoa: Malacosporea) (Hedrick et al 1993, Canning et al 2000, with bryozoans as invertebrate hosts (Anderson et al 1999, Longshaw et al 1999) and salmonids as vertebrate hosts (Feist & Bucke 1993, Hedrick et al 1993.…”

“…Here, T. bryo salmonae multiplies and differentiates from extra sporogonic stages, mainly in the renal interstitium, to sporogonic stages in the tubular lumen. In young-of-the-year (YOY), proliferative and granulomatous nephritis and necrotizing vasculitis with thrombus formation are host reactions to parasite infestation (Hedrick et al 1993, El-Matbouli & Hoffmann 1994, Bettge et al 2009). In laboratory studies, we pre viously showed that surviving fish can recover with complete regeneration of renal morphology (Schmidt-Posthaus et al 2012).…”

Proliferative kidney disease (PKD) of rainbow trout: temperature- and time-related changes ofTetracapsuloides bryosalmonaeDNA in the kidney

“…Increasing water temperature is associated with an increasing release of infective spores from bryozoans (Tops et al 2006), which may result in enhanced infection pressure on the fish. At the same time, higher water temperature may promote parasite proliferation in the fish host as suggested by Bettge et al (2009) and Gay et al (2001), and the resulting increase of infection intensity could then lead to the temperaturerelated elevation of mortality. Another aspect is that the fish immune system is modulated by water temperature (Le Morvan et al 1997 ;Köllner and Kotterba, 2002).…”

Kidney pathology and parasite intensity in rainbow trout Oncorhynchus mykiss surviving proliferative kidney disease: time course and influence of temperature

“…The main target organ is the kidney (Kent & Hedrick 1985) where T. bryosalmonae undergoes multiplication and differentiation from extrasporogonic to sporogonic stages (Kent & Hedrick 1985). Infected salmonids can excrete spores via the urine (Kent & Hedrick 1985, Morris et al 2002, Hedrick et al 2004, Bettge et al 2009a and transmission of the parasite from fish to bryozoans via excreted spores has been shown for brown trout Salmo trutta and brook trout Salvelinus fontinalis (Morris & Adams 2006, Grabner & El Matbouli 2008.…”