DETECTION OF CARP ANTIBODIES TO SPRING VIREMIA OF CARP VIRUS BY A COMPETITIVE IMMUNOASSAY

A competitive immunoassay for the detection of spring viraemia of carp virus (SVCV) antibodies in fish was developed in order to screen fish stocks for previous exposure to the virus. SVCV has been isolated from different fish species and the use of a competitive immunoassay overcomes the requirement of standard immunoassays for antisera prepared against the immunoglobulin of each species under test; instead, the test fish serum competes with an antiserum against SVCV for binding sites on the virus. The competitive assay was developed and tested using sera from common carp containing antibodies that had been induced either experimentally, or as a result of field exposure to the virus. When immunoassay results were compared with results of virus neutralisation tests on the sera from 2 groups of experimentally challenged fish, there was no correlation between the 2 techniques. Similar results were obtained with 4 groups of field-collected sera. One group had 34.6% neutralisation-positive sera, but 88.5% immunoassay-positive sera. The 3 remaining groups were negative by virus neutralisation, but each group had a small number (11.4, 8.3 and 11.5% respectively) of immunoassay-positive sera. The competitive immunoassay thus appears to be more sensitive than the neutralisation test. The assay has potential for use in large-scale screening of fish populations but further validation on a wider range of sera is needed.