Detection of specific IgM antibodies to infectious bronchitis virus by an antibody-capture ELISA

The results of a new antibody-capture ELISA (alpha-IgM-IBV ELISA), specific for IgM directed against Infectious Bronchitis Virus (IBV) show that this assay is a useful tool for diagnosing IBV infections. The data include individual results of the alpha-IgM-IBV ELISA in sequential SPF chicken sera after vaccination with H120 and challenge with M41, the specificity is based on results of 499 SPF sera, and the sensitivity on sera from experimentally vaccinated and challenged birds. Also reported are ELISA results on 168 field sera originating from seven broiler flocks (24 samples per flock) collected during the acute phase of an IBV infection. The alpha-IBV-IgM ELISA results obtained with field sera from broiler flocks infected by Massachusetts, D207, D212 or an unidentified serotype of IBV indicated that the ELISA, in which only M41-strain was used as antigen, was able to detect IgM responses to IBV serotypes other than Massachusetts. The specificity of the alpha-IBV-IgM ELISA was 99%, the sensitivity based on the experimental vaccination was 83 to 100%, depending on the day post vaccination. The sensitivity, based on the experimental challenge, was 83%, while the sensitivity, based on 168 field sera, was 93.5%. The IgM responses were rapid and transient and therefore indicative for acute IBV infections.