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The routine technique for detecting antibodies specific to infectious bursal disease virus is a serological evaluation by enzyme linked immunosorbent assay (ELISA) with preparations of whole virions as antigens. To avoid the use of complete virus in the standard technique, in-house VP2 and VP3 based ELISAs were developed. Accordingly, four types of indirect ELISAs viz., a commercial IDEXX-ELISA kit, VP2 and or VP3 antigen based ELISAs and a whole virus ELISA were compared with the virus neutralization test. It was concluded that the sensitivity and specificity at receiver-operating characteristics (ROC) optimized cut-off of four ELISAs viz., IDEXX-ELISA, VP2-ELISA and VP3-ELISA indicated similar performance whereas whole virus antigen based ELISA showed poor performance in comparison to other ELISAs. Similarly the positive and negative likelihood ratio of four ELISAs at an optimized cut-off indicated IDEXX-ELISA to be the best among all the four ELISAs while the performance of rVP3-ELISA and rVP2-ELISA is good as compared to the whole virus ELISA. Finally, the area under the ROC curve (AUC) of four ELISAs which represented a summary statistics of the overall diagnostic performance of the test also indicated that the IDEXX-ELISA, VP3-ELISA and VP2-ELISA had similar and relatively better performance when compared to whole virus antigen-ELISA., (Copyright 2010 Elsevier B.V. All rights reserved.)

Infectious bursal disease virus (IBDV) is an immunosuppressive disease of young chicken characterized by severe depletion of B-lymphocytes in the bursa of Fabricius. To provide antigen for diagnostic tests, its major structural protein VP2 was expressed in the yeast Saccharomyces cerevisiae. Electron microscopy of purified VP2 protein demonstrated that when expressed from yeast cells VP2 protein forms subviral particles (SVPs) of approximately 20nm in diameter. A recombinant VP2 antigen-based single serum dilution enzyme linked immunosorbent assay (ELISA) using the SVPs detected IBDV specific antibodies in chickens. A linear relationship was found between the predicted antibody titres at a single working dilution of 1:1000 and the corresponding observed serum titres when determined by the standard serial dilution method. Regression analysis was used to construct a standard curve from which an equation was derived which confirmed their correlation. The equation was then used to convert the corrected absorbance readings of the single working dilution directly into the predicted ELISA antibody titres. The assay proved to be sensitive, specific and accurate as compared to the serum neutralization test and agar gel immunodiffusion test. The recombinant VP2 antigen is a suitable alternative to whole viral antigen.