DAO 64:37-44 (2005)  -  doi:10.3354/dao064037

Characterisation of an emerging rickettsia-like organism in Tasmanian farmed Atlantic salmon Salmo salar

Serge Corbeil*, Alex D. Hyatt, Mark St. J. Crane

AAHL Fish Diseases Laboratory, Australian Animal Health Laboratory, CSIRO Livestock Industries, Private Bag 24,Geelong, Victoria 3220, Australia

ABSTRACT: A rickettsia-like organism (RLO) was observed in farmed Atlantic salmon Salmo salar located in south-east Tasmania, Australia. Several assays such as immunoperoxidase, immunoelectron microscopy, polymerase chain reaction and nucleic acid sequencing, as well as phylogenetic analysis of rDNA sequences, were performed on infected fish tissues. Immunohistochemistry results suggested the presence of related antigenic determinants between the Tasmanian RLO and the type strain LF-89 of Piscirickettsia salmonis. However, sequence alignment demonstrated that the Tasmanian RLO contains a 19 bp deletion at the 3’-end of the internal transcribed spacer region of the rDNA operon, indicating a genetic divergence from P. salmonis isolates, which are exotic to Australia.


KEY WORDS: Rickettsia-like organism · rDNA sequences · Differential antigenicity · Piscirickettsia salmonis · Atlantic salmon


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