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J. J. De Wit1*, D. R. Mekkes1, G. Koch2 & F. Westenbrink1
The results of a new antibody-capture ELISA (a-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 a-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.
Introduction
Infectious bronchitis virus (IBV) is a major cause of respiratory problems in broilers and of poor egg production in breeders and layers. Acute IBV infections may be diagnosed by virus isolation or immunofluorescence assay (IFA) (Hilbink et al., 1982). More often, the diagnosis is based on serology, for which two methods can be used. Routinely, detection of a seroconversion, using paired serum sets (de Wit et al., 1997) is performed. Available tests are group-specific ELISAs, serotype-specific haemagglutination inhibition (HI) and virus neutralisation (VN) tests (de Wit et al., 1997). This testing of paired sera is expensive and impractical as it takes several weeks to complete.
Alternatively, it is possible to look for an IBVspecific IgM response. Because IBV-specific IgM is only present temporarily after infection or vaccination (Gillette, 1974; Mockett & Cook, 1986; Martins et al., 1990, 1991), its detection is indicative of a recent infection or vaccination. Therefore, one sampling is enough. A sensitive...