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The specificity and rapidity of coagglutination test for the serological typing of IPNV isolated in cell cultures or for the direct detection of IPNV antigen in fish tissues were studied.Coagglutination tests were carried out with cell free virus antigens from selected viruses using Staphy lococcus aureus (Cowan I) sensitized with anti-IPNV (Buhl) serum. Positive reactions occured only with cell free IPNV (Buhl) antigen, and no cross reactions were observed.The specificity of coagglutination test for rapid (less than 2h) serological typing of IPNV was tested using the strains from North America, Japan and Europe. Staphylococci sensitized with anti-VR 299 serum gave positive reactions with the strains from North America and Japan (VR 299 type), but did not combine with the strains from Europe (Sp and Ab type). Although staphylococci sensitized with anti-Sp and Ab sera showed weak cross reactions with the strains from North America and Japan, the agglutination pattern was clearly different.The most important use of the coagglutination test for IPNV would be to detect specific IPNV antigen in the internal organs of infected fish. It was found that IPNV antigen could be detected in extracts of IPNV infected rainbow trout (Salmo gairdneri), coho salmon (Oncorhynchus kisutch) and amago salmon (Oncorhynchus rhodurus) tissues at relatively high sensitivity.The results obtained in this study using the coagglutination test for the diagnosis of IPN indicate that this rapid and simple test, which requires no special apparatus and can be performed in the field, is a valuable addition to the diagnostic methods available for detecting this disease.

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