Molecular epidemiology of infectious bursal disease virus in the Near East and Persian Gulf regions

Infectious bursal disease virus (IBDV) is a ubiquitous immunosuppressive pathogen which is a severe burden to the poultry industry. Due to frequent mutation and reassortment events, its double-stranded, bi-segmented RNA genome displays a considerable heterogeneity, which in turn produces profound differences in antigenicity and pathogenicity. In recent years, the investigation of IBDV epidemiology has greatly benefited from the proposal of multiple phylogenetic classification systems which prompted the execution of molecular surveys all over the world, producing a wealth of standardized and easily sharable data. The present epidemiological survey was conducted in six Near East and Persian Gulf countries to characterize the field IBDVs circulating in the region. Ninety-three broiler flocks, immunized with different vaccination protocols, were investigated over a one-year period by collecting eight individual bursal samples at a time. Using molecular assays targeting both genome segments, field IBDVs belonging to four genotypes were detected from 42 flocks across all investigated countries. While traditional very virulent IBDVs (genotype A3B2) represented a minority, multiple atypical IBDV genotypes (A3B1, A4B1 and A6B1) were found to circulate in most of the region. Many of the detected strains were related to sequences from other continents, supporting the involvement of the Near and Middle East in complex networks of viral spreading. The obtained results, combined with the available literature, allowed us to update the epidemiological picture, hopefully favouring the identification of epidemiological threats and the planning of effective monitoring and control strategies. RESEARCH HIGHLIGHTS: Different field IBDVs were found to circulate in the Near and Middle East. Multiple atypical genotypes (A3B1, A4B1, A6B1) were found to circulate extensively. Traditional very virulent IBDVs (A3B2) were a minority of the detected strains. Viral exchanges can be hypothesized between the region and different continents.