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 Scares. All samples were obtained f rom commercially reared chicken flocks experiencing signs typical of infect ious bursal disease. The reverse transcriptase/polymerase chain reaction (R T/PCR) technique was used to detect the viruses and restriction fragment le ngth polymorphism (RFLP) was used to compare a 743-bp region of the VP2 gen e 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 presen ce of an SspI site in the 743-bp RT/PCR fragment was used to predict the ve ry virulent (vv) phenotype. Almost half (49%) of the viruses detected had t he same RFLP with the BstNI and MboI enzymes. These viruses were placed int o a new molecular group, designated group 6, chat was exemplified by the RS 593 vaccine strain of IBDV, which also had this molecular RFLP pattern. Som e viruses detected had RFLP patterns similar to molecular groups 2, 3, and 4, previously described in our laboratory. Sixteen RFLP patterns were obser ved that did not match RFLP results we previously obtained for vaccine IBDV strains. The SspI restriction site was found in 46% of the viruses detecte d, predicting that these viruses have the vvIBDV phenotype. The SspI site w as not observed in viruses from Central and South America.