The diversity of infectious bursal disease viruses Literature review

The authors provide an update on the recognized genetic variants and main features of infectious bursal disease viruses (IBDV). The traditional classification of IBDV was based either on the pathogenicity and the antigenicity of the viruses, resulting in confusions sometimes. A new system, based on the more objective molecular characteristics of the viruses was proposed and published recently, which might well be of interest for the readers of the Hungarian Veterinary Journal too. Therefore, a short summary of the new system is provided. Becoming of the molecular methods a commonplace in diagnostic labs enabled a more refined picture on the genetic compositions of IBDVs. In particular, the occurrence of reassortant viruses has been reported recently more and more frequently. The exchange of the genomic segments between viruses may not only alter the virulence of the resulting strain but may cause diagnostic/classification issues too. Having that in mind it is reasonable to test for both genome segments to provide a clear picture on the strains in question. Also recently the circulation of "subclinical" IBDVs was reported from Central Europe, with close homology to some South American counterparts, which is alerting from the point of view of efficient and global spreading of IBDVs. This is further supported by the observations that IBDV infections may remain undetected in flocks recording loss of performance, reduced feed conversion, poor immune responses to vaccination - without the pathognomonic signs of IBDV. All these aspects clearly emphasize the importance of monitoring the flocks for the presence of IBDV, certainly besides other relevant pathogens.