Full-genome analysis of a new Italian genotype of Infectious bursal disease virus.

Infectious bursal disease virus (IBDV) causes a worldwide, contagious disease of young chickens, also known as “Gumboro disease”. Since its appearance in 1965, the disease has become endemic in Italy. In a recent study an emerging IBDV genotype (ITA) was detected in IBDV-live vaccinated broilers without IBD clinical signs. VP2 sequence analysis showed that strains of the ITA genotype clustered separately from other reference strains, either classical or very virulent (vv) and from vaccines. In order to obtain a more exhaustive molecular characterization of IBDV ITA genotype and speculate its origin, full genome sequence of the field isolate IBDV/Italy/1829/2012 was determined and sequence, phylogenetic and recombination analysis performed. Results confirmed ITA to be a genetically distinctive IBDV genotype. Interestingly, multiple amino acid (aa) sequence alignment revealed that it shared several aa residues with vv IBDV strains, as well some virulence markers, especially in the VP1 protein. Nevertheless sequence analysis highlighted in ITA strain the presence of some residues typical of IBDV strains at low degree of virulence. Although homologous recombination and reassortant phenomena may naturally occur between different IBDV strains, no evidence of those events was found in the genome of the studied ITA strain.