Development of a PCR procedure for the detection of a herpes-like virus infecting oysters in France

A PCR-based procedure for detecting a herpes-like virus that infects the Ja panese oyster, Crassostrea gigas, in France was developed. Two primers were designed to provide specific amplification products ranging in size from 9 17 to 1001 bp when carried out on oyster herpes-like virus DNA. No amplific ation was observed of oyster genomic DNA nor of the DNA from vertebrate her pesviruses. Crude samples were prepared and submitted to nested PCR, allowi ng amplification of DNA fragments of the expected size when carried out on infected larval and spat samples. The procedure used to prepare the sample for PCR was found to be critical because of the presence of unidentified su bstances in oyster tissues that inhibit the PCR reaction. A rapid and conve nient sample preparation using ground tissues allowed a sensitive detection of the herpes-like virus infected oysters. The ability of the defined PCR protocol to diagnose herpes-like virus infections in oysters was compared t o the transmission electron microscopy technique using 15 C. gigas larval b atches with or without mortalities. PCR amplification is as sensitive a dia gnostic assay for herpes-like virus as transmission electron microscopy. Ho wever, the nested PCR protocol is more convenient and less time consuming. The relationship between reported mortalities among C. gigas oyster spat an d herpes-like virus DNA detection by PCR was also investigated. Statistical analysis showed that virus detection and mortalities are correlated. This observation highlights the importance of studying the causative role of her pes-like virus in oyster spat mortalities. (C) 2000-Elsevier Science B.V. A ll rights reserved.