USE OF CLONED CDNA PROBES FOR DIAGNOSIS OF INFECTIOUS PANCREATIC NECROSIS VIRUS-INFECTIONS

A dot-blot hybridization test has been developed for the detection of infectious pancreatic necrosis virus (IPNV) in infected fish. For this purpose, cloning of the dsRNA of the West Burton strain of IPNV was carried out. Two cDNA clones (WB and A4) were characterized for use as diagnostic probes and corresponded to IPNV genome segments A and B, respectively. Clone WB1, with an insert of 812 base pairs, showed an 87 and 77% nucleotide sequence homology with the corresponding sequences of Jasper and N1 strains, respectively. Clone A4, with an insert size of 596 bp, presented a nucleotide sequence homology of 90 and 80% with the corresponding sequences of the Jasper and Sp strains, respectively. Both probes were able to detect 15 ng of purified dsRNA, and were highly efficient in detecting the RNA of American IPNV strains. However, the Ail probe was less effective than WB1 in hybridizing to RNA from European and Spanish strains of IPNV. Both probes detected IPNV RNA in cells 4-8 h post-infection with the homologous West Buxton strain, 8-12 h post-infection with other American strains and 24 h post-infection with the European strains of IPNV. The method was less sensitive in detecting IPNV RNA directly in infected fish tissues. However, the present authors obtained a 100% effectiveness to detect viral RNA in cells inoculated with fish tissues confirmed by conventional diagnostic methods as being infected with IPNV. Therefore, the hybridization test is appropriate if combined with conventional diagnostic procedures, eg applying the dot blot hybridization test on tissue cultures 12-24 h after inoculation with infected fish tissue homogenates.