Chicken anaemia virus antibody ELISA: problems with non-specific reactions

For accreditation of CSIRO specific pathogen-free flocks, chicken sera are routinely tested for antibody to chicken anaemia virus (CAV) using a commercially available ELISA kit. On some occasions recently, up to 18.2% positive reactions have been found in individual isolators, with an overall reaction rate of 2.7%. On subsequent bleeding the majority of the suspected birds have given negative reactions, indicating that the earlier reactions were false-positives. The protein composition of the sera that appeared CAV-negative or -positive in the ELISA were compared using various Chromatographic techniques. Separation of serum proteins by high resolution size exclusion chromatography revealed that in the false-positive sera the antigen-binding activity is associated with a protein fraction which was different from that found in the true-positive sera.