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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. 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. [ABSTRACT FROM AUTHOR]

Infectious bursal disease virus (IBDV) is a highly contagious birnavirus causing a burdensome immunosuppressive disease in chickens. IBDV features a remarkable antigenic, pathogenic and genetic heterogeneity, with significant implications on disease manifestation, control measures and diagnostic approaches. The recent proposals of comprehensive phylogenetic classification systems offered the ideal platform for large-scale molecular surveys, which are crucial to gather epidemiological data and inform control efforts. In this study, the IBDV scenario was investigated in most of Western Europe by considering the results of diagnostic activities performed internationally throughout 2021. In total, 470 bursal samples from nine different countries were analysed by RT–PCR targeting the VP2. When a field virus was identified, the VP1 was also characterized. Most of the 132 detected field viruses were highly homologous reassortants featuring a very virulent-like VP2 and a classical-like VP1 (genotype A3B1). Despite emerging recently, these reassortants were already signalled in several countries in North-Western Europe and associated with subclinical infections. Here, we report their further spread in the region, where they currently represent the dominant field threat. Two other IBDV types were found, one in Italy, where all the identified viruses clustered in a clade of the A3B1 genotype previously reported only in Russia and the Middle East, and the other in Portugal, where the recently characterized A9B1 genotype was confirmed to circulate. The obtained data suggest the recent occurrence of a major shift in the Western European epidemiological landscape of IBDV, stressing the importance of steady monitoring and sharing of information among different countries and laboratories. RESEARCH HIGHLIGHTS The IBDV scenario in Western Europe seems to have radically changed in recent years. IBDV reassortants were found to be the dominant field type in the region. Local circulation of two other IBDV types was detected in Italy and Portugal. [ABSTRACT FROM AUTHOR]

Infectious bursal disease virus (IBDV) is an immunosuppressive pathogen with a bi-segmented, double-stranded RNA genome. Two serotypes, named 1 and 2, are recognized, and serotype 1 is traditionally divided into classical, variant and very virulent strains. Despite having great practical relevance, this classification lacks standardization and may therefore generate confusion. The widespread adoption of molecular techniques, which allow direct assessment of either pathogenicity or antigenicity, further complicates this scenario. Recently, two phylogeny-based classification methods have been proposed to obtain informative and standardized results. The first is based on the analysis of the capsid protein VP2 gene, considered as the main determinant of virulence, while the other one considers both VP2 and RNA polymerase VP1, located in different genome segments. The latter approach is therefore better suited to detect reassortment events, which play a significant role in IBDV evolution. This work reports the detection of eight strains in Portuguese broiler farms that diverged from all available IBDV sequences. Subsequent analyses of VP1 and VP2 sequences confirmed that these strains form a new genotype having segment A of a new genogroup and segment B of classical-like genogroup. No recombination events were identified, while several unique amino acid changes were found in key positions within the VP2. This discovery emphasizes the importance of steady and attentive monitoring of IBDV epidemiology. Further research efforts will be devoted to characterizing the novel genotype, by isolating new strains, assessing their pathogenicity and determining the level of protection ensured by commonly administered IBDV vaccines. Eight IBDV strains with unique VP2 features were detected in Portugal. Based on two distinct classification methods, the strains belong to a new genotype. [ABSTRACT FROM AUTHOR]