Restriction fragment length polymorphisms in the VP2 gene of infectious bursal disease viruses.

Infectious bursal disease viruses (IBDVs) were examined for restriction fragment length polymorphisms in a fraction of the VP2 gene with the use of the reverse transcriptase/polymerase chain reaction-restriction fragment length polymorphism (RT/PCR-RFLP) assay. The restriction enzymes BstNI and Mbol were used to obtain RFLP results. A third enzyme, StyI, was tested, but its utility for differentiation of IBDV strains was limited. Thirteen vaccine viruses and five IBDV strains that were previously characterized were placed into five molecular groups. Two groups contained viruses described as being classic strains, and two groups contained viruses described as being variant strains. The fifth group contained both classic and variant strains. The RFLP observed for the serotype 2 IBDV strain OH was unlike any of the RFLPs observed in viruses in the five molecular groups. Seven IBDV strains from commercially reared chickens in the United States, Mexico, Puerto Rico, and Thailand were tested in the RT/PCR-RFLP assay to determine if they were similar to the commercial IBDV vaccine strains tested. These viruses were selected because they were associated with lesions in the bursa of chickens that should have been protected by maternal antibodies or active immunity. Each of the viruses tested contained a unique RFLP compared with the IBDV strains and vaccine viruses examined in this study and, thus, did not fit into any of the five molecular groups. These viruses also were distinguishable from each other.