Amino acid comparison of infectious bursal disease viruses placed in the same or different molecular groups by RT/PCR-RFLP

Infectious bursal disease virus (IBDV) strains have been identified and pla ced into molecular groups by a reverse transcriptase (RT)/polymerase chain reaction (PCR)restriction fragment length polymorphism (RFLP) assay. The pr edicted amino acid sequences corresponding to the region of the genome exam ined by RFLP were determined and compared for 14 IBDV strains from differen t molecular groups and 11 IBDV strains that were identified in molecular gr oup 6. Among the viruses within molecular group 6, 13 amino acid positions had mutations, and among the viruses in different molecular groups, 27 amin o acid positions had mutations. In addition to having more mutations, virus es compared from different molecular groups also had mutations at key posit ions that were previously reported to be important for the formation of neu tralizing epitopes. Three of these IBDV strains with unique RFLP patterns w ere used to challenge l-wk-old broiler chickens with maternal immunity to I BDV. One of these viruses, T1, broke through this maternal immunity as evid enced by detection of the virus by RT/PCR-RFLP and production of an active virus neutralizing antibody response to classic and variant IBDV strains. U nique amino acid mutations in the T1 virus that may have contributed to its ability to break through this maternal immunity were observed at amino aci ds 318 and 322. The results indicate that RFLP profiles and nucleotide sequ ences can be used to predict the relative similarities and differences amon g IBDV strains, but determining the actual antigenic differences among viru ses requires testing in vivo.