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Avian infectious bronchitis is ubiquitous and highly contagious disease of poultry, with profound effect on commercial poultry production. For effective control of infectious bronchitis virus (IBV), quick and specific diagnosis is of utmost importance. In this study, the virus was isolated from clinical samples from India and the full length nucleocapsid (N) gene was amplified, cloned and expressed in a prokaryotic system. The purified recombinant N protein based single serum dilution enzyme linked immunosorbent assay (ELISA) was developed for IBV to measure specific antibody in the sera of chickens. A total of 310 chicken sera samples were tested using the commercial IDEXX kit along with the assay developed. A linear correlation was obtained between predicted antibody titres at a single working dilution of 1:100 and the corresponding serum titres observed as 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 developed equation was then used to extrapolate predicated ELISA antibody titer from corrected absorbance readings of the single working dilution. The assay proved to be specific (95.8%) and sensitive (96.8%) when compared to the commercial IDEXX ELISA test. [ABSTRACT FROM AUTHOR]

Abstract: 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. [Copyright &y& Elsevier]