Clinical Outbreaks of Bacterial Kidney Disease (BKD) in Hatchery-Raised Brook Trout (Salvelinus fontinalis) (Mitchill, 1814): Lessons Learned

Abstract

A number of clinical Bacterial Kidney Disease (BKD) outbreaks caused by Renibacterium salmoninarum infection among the hatchery reared brook (BKT) trout lots were presented during 2002-2004 to the Aquatic Animal Health Laboratory, Michigan State University, MI, USA. Diagnosis of these mortality episodes was performed thorough clinical examination, quantitative enzyme-linked immunosorbant assay (Q-ELISA), nested polymerase chain reaction (nPCR), culture, histopathology and immunohistochemistry (IHC). The possible causes that lead to the initiation and progression of such outbreaks have been investigated. Although Q-ELISA, nPCR and culture results for all of the examined cases indicated a heavy infection with R. salmoninarum, inconsistent results were obtained by histopathology and immunohistochemical examination of the paraffin embedded blocks of the formalin fixed kidney tissues. This study also included assessment of R. salmoninarum infection status in a subsample of BKT broodstocks of the same hatchery. Results indicated the presence of chronic infection in the broodstock with BKDpathognomonic granulomas occupying fairly large portions of the kidney tissues.