Detection of antibodies against infectious bronchitis virus strain QX (GI-19) by commercial ELISA kits and virus neutralization test.

The study assessed the suitability of four commercially available IBV ELISA kits for detecting antibodies against the QX strain of IBV in poultry. Two experiments were conducted: one in SPF layers under laboratory conditions and another in broiler chickens under field conditions. Chickens were vaccinated with either a candidate vaccine or existing commercially available vaccines against QX strain of IBV. Sera and tear samples were collected post-vaccination and analysed using various ELISA and virus neutralization tests. Results show that all ELISA kits have detected antibodies induced by the candidate vaccine, with antibody levels comparable to or higher than those induced by existing vaccines. The BioChek indirect ELISA kit detected the highest antibody levels in the first experiment, while the ID Screen indirect ELISA kit detected the highest antibody levels in the second experiment. Virus-neutralizing antibodies were found in most vaccinated groups, but not in the unvaccinated control group. Tear samples indicated local antibody development peaking at 28 days post-vaccination. Although the antibody levels in the sera of vaccinated chickens do not always correlate with protection against infection, and the role of local antibodies remains controversial, measuring antibodies by ELISA provides an indication of successful vaccination or field challenge. In conclusion, this study highlights the importance of establishing a baseline standard for expected titer values through regular serological monitoring.