Molecular typing of infectious bursal disease virus of Israeli field and vaccine strains by the reverse transcription/polymerase chain reaction/restriction fragment length polymorphism assay.

Infectious bursal disease viruses (IBDVs) were examined by testing bursa samples from 37 commercially reared chicken flocks and three vaccine strains by the reverse transcription (RT)/polymerase chain reaction (PCR)/restriction fragment length polymorphism assay (RFLP). The assay was conducted with a 717-bp fragment of the VP2 gene with the restriction enzymes BstNI and MboI. The presence of a restriction site for SspI was used to predict a very virulent phenotype. Results indicated the existence of two molecular groups within the field isolates; four samples showed one pattern of RFLPs, and the majority, 30 out of the 37 tested, showed a second RFLP pattern. Three samples tested negative for IBDV. Eight bursa samples, representing the two molecular groups, were also tested by the RT/PCR/RFLP assay as developed by Jackwood. A comparison of the RFLP profiles by the two methods indicated that four isolates belonged to molecular group 6 and 30 isolates belonged to a new molecular group. All field isolates had a very virulent phenotype. One vaccine strain, produced from a local isolate, was classified as molecular group 6. The other two vaccine strains had RFLPs that differed from those of the field isolates.