Rapid diagnosis of red sea bream iridovirus infection using the polymerase chain reaction

A simple and sensitive polymerase chain reaction (PCR) based assay is described for detection of the red sea bream iridovirus (RSIV) in infected fish. The assay involves amplification of a portion of the ribonucleotide reductase small subunit (RNRS) gene of the virus from DNA isolated from the spleen. The system was tested on red sea bream following an experimental infection. In our infection model, disease signs first became apparent 5 to 6 d post-infection, and mortality commenced at Day 6 and reached 90% by Day 9. No amplified product was detected from fish at 1 or 2 d post-infection, but 3 of 5 fish tested positive at Day 3, and all fish tested positive at Days 5 and 8. Thus, infection could be detected prior to the appearance of overt symptoms. This PCR method should be of considerable value for aquaculture to detect RSIV infection.