Abstract

Infectious bursal disease (IBD) is a contagious viral disease of young chickens that causes immunosuppression, mortality, and growth retardation. This pathology has severely affected the Moroccan poultry industry. The objective of the present study was the isolation, molecular characterization, and histopathology examinations of infectious bursal disease virus collected from 49 suspected farms from different regions of the country from 2013 to 2016. The real-time PCR results indicated that 41 out of 49 farm cases were found positive with a prevalence of 41% for classical virulent IBD virus (IBDV) and 59% for very virulent IBDV (vvIBDV). Pathological examinations showed the presence of two types of lesions, including acute to subacute lesions with a prevalence of 86%, and the sub-chronic to chronic lesions with a prevalence of 14%. The nucleotide and deduced amino acid sequences for the hypervariable region of VP2 for 7 vvIBDVs were compared to worldwide IBDV isolates and the findings suggested that it belonged to a group of very virulent strains. Phylogenetically, all the Moroccan vvIBDV field isolates were grouped in the same cluster with Malaysian and European vvIBDV isolates. This report demonstrated the continuous circulation of vvIBDV in commercial poultry farms in Morocco since 2013.