Piscirickettsiosis is a disease of salmonids caused by Piscirickettsia salmonis that was first reported in farmed coho salmon (Oncorhynchus kisutch). The disease was initially described in 1989 from fish in Chile. Piscirickettsia salmonis is a Gram-negative, highly fastidious, intracellular bacterial pathogen of fish. It is distantly related to the genera Coxiella and Francisella and is grouped with the gamma subdivision of the Proteobacteria.
The identification of P. salmonis is based on isolation of the causative agent with subsequent testing for characteristics of this intracellular pathogen. Piscirickettsia salmonis occurs in cytoplasmic vacuoles in the host cell. The organism may be distinguished from Chlamydia as it does not possess the characteristic chlamydial developmental cycle, and does not contain the group-specific lipopolysaccharide chlamydial antigen. The identity is confirmed by means of serological tests or polymerase chain reaction ( PCR ) .
For a rapid result, the identity of P. salmonis isolated in cell culture or observed in smears from diseased tissue may be confirmed by means of the fluorescent antibody test or immunohistochemical methods with polyclonal or monoclonal antibodies, or by PCR with P.-salmonis -specific primers.
The implementation of hygienic measures and management policy are the only control methods currently available. Antibiotics have been used, but their value is questionable. Intensive efforts are underway by various groups to develop an effective vaccine.