Detection by immunofluorescent assay of serotype‐specific and group‐specific antigens of infectious bronchitis virus in tracheas of broilers with respiratory problems

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Abstract
The performances of seven immunofluorescent assays (IFAs) for infectious bronchitis virus (IBV) were examined on 115 trachea samples collected from 60 broiler flocks with clinical respiratory distress. Whether IBV strains could be serotyped directly on trachea sections by IFAs was examined using four different serotype-specific monoclonal antibodies (MAbs). Two group-specific IFAs using two different group-specific MAbs, were compared with a conventional IFA using a chicken hyperimmune anti-IBV serum. The use of the six MAbs in the IFA showed, in contrast to the use of the hyperimmune serum, no or only faint non-specific staining. Although the sensitivities of the two group-specific IFAs using MAbs were not higher (P> 0.05, power 80%) than the sensitivity of the IFA using hyperimmune serum, the interpretation of the staining of the first two IFAs was easier. Seventeen of the 41 isolated IBV strains could be typed by IFA using the serotype-specific MAbs. Serotyping by IFA was possible in about 70% of the tracheas that stained positive with group-specific MAbs or hyperimmune serum and from which IBV was isolated. Use of serotype-specific IFAs is a new and very fast way of diagnosing IBV infections including serotyping, providing enough time to adjust the vaccination programme for the next broiler flock.