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Proliferative Kidney Disease and Proliferative Darkening Syndrome are Linked with Brown Trout (Salmo trutta fario) Mortalities in the Pre-Alpine Isar River

1
Institute for Infectious Diseases and Zoonoses, LMU Munich, 80539 Munich, Germany
2
German Center for Infection Research (DZIF), Partner Site Munich, 80539 Munich, Germany
3
Research Unit Analytical Pathology, Helmholtz Zentrum Munich, 85764 Neuherberg, Germany
4
Bavarian Environment Agency, Unit Aquatic Toxicology, 82407 Wielenbach, Germany
5
Clinical Division of Fish Medicine, University of Veterinary Medicine, 1210 Vienna, Austria
*
Author to whom correspondence should be addressed.
Pathogens 2019, 8(4), 177; https://doi.org/10.3390/pathogens8040177
Received: 1 September 2019 / Revised: 3 October 2019 / Accepted: 4 October 2019 / Published: 6 October 2019
(This article belongs to the Section Animal Pathogens)
For many years, brown trout (Salmo trutta fario) mortalities within the pre-alpine Isar River in Germany were reported by the Bavarian Fisheries Association (Landesfischereiverband Bayern e.V.) and local recreational anglers during August and September. Moribund fish seemed to be affected by proliferative darkening syndrome (PDS). In addition, proliferative kidney disease (PKD) caused by Tetracapsuloides bryosalmonae was discussed. To investigate this phenomenon, the present field study monitored brown trout mortalities by daily river inspection in 2017 and 2018. Moribund brown trout (n = 31) were collected and examined using histology, immunohistochemistry, qPCR, and quantitative stereology. Our investigations identified 29 (93.5%) brown trout affected by PKD. Four brown trout (12.9%) displayed combined hepatic and splenic lesions fitting the pathology of PDS. The piscine orthoreovirus 3, suspected as causative agent of PDS, was not detectable in any of the samples. Quantitative stereological analysis of the kidneys revealed a significant increase of the renal tissue volumes with interstitial inflammation and hematopoietic hyperplasia in PKD-affected fish as compared to healthy brown trout. The identified T. bryosalmonae strain was classified as part of the North American clade by phylogenetical analysis. This study highlights PKD and PDS as contributing factors to recurrent autumnal brown trout mortalities. View Full-Text
Keywords: immunohistochemistry; PDS; piscine orthoreovirus 3; PKD; quantitative stereology; Tetracapsuloides bryosalmonae immunohistochemistry; PDS; piscine orthoreovirus 3; PKD; quantitative stereology; Tetracapsuloides bryosalmonae
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Arndt, D.; Fux, R.; Blutke, A.; Schwaiger, J.; El-Matbouli, M.; Sutter, G.; Langenmayer, M.C. Proliferative Kidney Disease and Proliferative Darkening Syndrome are Linked with Brown Trout (Salmo trutta fario) Mortalities in the Pre-Alpine Isar River. Pathogens 2019, 8, 177.

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