Complete genome analysis and time scale evolution of very virulent infectious bursal disease viruses isolated from recent outbreaks in Morocco.

ABSTRACT

Emerging of very virulent infectious bursal disease virus (vvIBDV) genotype in poultry flocks in Morocco were characterized. VP2 sequence analysis showed that the strains of Moroccan vvIBDV genotypes clustered separately from classic and vaccine strains reference of IBDV. The full-length genome of four Moroccan vvIBDV strains was determined, in order to get a more exhaustive molecular characterization allowing to conduct the evolution time scale and speculations on their origin. In a phylogenetic tree, nucleotide sequences of segment A and B formed a common branch with those vvIBDV references strains published in GenBank, but they clearly grouped into a distinct subcluster. An alignment of deduced amino acid sequences segment B, confirmed the presence of the conserved TDN tripeptide found in all of the vvIBDV genotype and revealed the presence of 2 substitutions I472L and E688D specific for the vvIBDV Moroccan isolates. The deduced amino acid sequences of segment A genes showed the presence of the "signature" typical of the vvIBDV genotype and revealed the presence of 7 aa substitutions specific for the vvIBDV Moroccan strains. The evolution rate for IBDV VP2 gene was estimated at 5.875 × 10-4 substitutions/site/year. The estimation of the time to most common recent ancestor of Moroccan vvIBDV based on the VP2 sequences available was 31 years, corresponding to 3 years earlier than the first vvIBDV case detection in layers in the country.