IDENTIFICATION OF VERY VIRULENT INFECTIOUS BURSAL DISEASE VIRUSES BY RT-PCR OF VP1 GENE AND SPECULATION ABOUT THE POSSIBLE PRESENCE OF REASSORTANT VIRUSES

Infectious bursal disease virus (IBDV) genome is a bi-segmented RNA virus that encodes five viral proteins. The need for the development of a simple and rapid method to differentiate the IBDVs has prompted researchers to work on different viral proteins of these viruses. At the present study, an attempt was made to amplify a 715 bp fragment of VP1 gene by RT-PCR of 26 IBDV isolates that their virulence pattern had been previously determined by RT-PCR/REA of VP2 gene. The results showed that in 20 (76%) IBDV isolates, the virulence pattern (very virulent IBDV) were found to be identical using either RT-PCR of VP1 or RT-PCR/REA of VP2. However, in the remaining six IBDV isolates the results were different. Considering the available farm data from the viruses of this study which are in accordance with results on VP1, it is speculated that this finding may be due to the presence of reassortant IBDVs. These findings also indicate that the VP2 in not the sole determinant for the virulence in IBDV.