Restriction fragment length polymorphisms in the VP2 gene of infectious bursal disease viruses from outside the United States.

Infectious bursal disease viruses (IBDVs) were identified in bursa samples from chickens reared outside the United States. All samples were obtained from commercially reared chicken flocks experiencing signs typical of infectious bursal disease. The reverse transcriptase/polymerase chain reaction (RT/PCR) technique was used to detect the viruses and restriction fragment length polymorphism (RFLP) was used to compare a 743-bp region of the VP2 gene among the viruses detected. The 81 IBDVs detected were from 16 different countries and were assigned to molecular groups on the basis of their RFLP following digestion with the restriction enzymes BstNI and MboI. The presence of an SspI site in the 743-bp RT/PCR fragment was used to predict the very virulent (vv) phenotype. Almost half (49%) of the viruses detected had the same RFLP with the BstNI and MboI enzymes. These viruses were placed into a new molecular group, designated group 6, that was exemplified by the RS593 vaccine strain of IBDV, which also had this molecular RFLP pattern. Some viruses detected had RFLP patterns similar to molecular groups 2, 3, and 4, previously described in our laboratory. Sixteen RFLP patterns were observed that did not match RFLP results we previously obtained for vaccine IBDV strains. The SspI restriction site was found in 46% of the viruses detected, predicting that these viruses have the vvIBDV phenotype. The SspI site was not observed in viruses from Central and South America.