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[Objective] The study aimed to determine the pathogen type and molecular characteristics of suspected infectious bursal disease virus (IBDV) infections in a broiler farm in Yunnan in order to understand the prevalence and molecular evolution trends of novel reassorted IBDV strains in broilers and to provide a reference for formulating effective infectious bursal disease (IBD) prevention, control and vaccine selection strategies. [Method] Bursae of Fabricius from chickens suspected of IBDV infection were homogenized and tested using nested RT- PCR. Positive bursal tissue suspensions were inoculated into 9-day-old SPF chicken embryos for virus isolation. The VP2 and VPI-b genes of the virus were amplified and analyzed for genetic variation. [Result] A novel reassorted IBDV strain (named YN-YX221110) was successfully isolated. After inoculation into 9-day-old SPF chicken embryos, the embryos showed diffuse hemorrhages, with bleeding spots on the head, neck, and back skin. Based on the vVP2 gene sequence, the YN-YX221110 isolate showed the highest nucleotide similarity with novel variant strains (nvIBDV) reference strains, ranging from 93.2% to 97.9%. The vVP2 gene of the YN-YX221110 isolate shared characteristic amino acid positions 222A with the very virulent (vvIBDV) reference strains such as UK661 and HK46, and positions 249K, 256V, 279N, 284A, 294L and 299S with the novel variants IBDV (nvIBDV) reference strain SHG19. In the genetic evolutionary tree based on the vVP2 gene, the YN-YX221110 isolate clustered with nvIBDV reference strains such as GX-QZ191002 and SHG19, belonging to the A2d branch. Based on the VPI-b gene sequence, the YN-YX221110 isolate showed the highest nucleotide similarity with classical virulent (cIBDV) strains, ranging from 97.8% to 98.4%. The characteristic amino acid positions of the vVP2 gene in the YN-YX221110 isolate, 240D, 242D, 287T, 390L and 393E, were the same as those in attenuated (attIBDV) reference strains such as B87 and Gt; In the phylogenetic tree based on the VP1-b gene sequence, the YN-YX221110 isolate clustered with attIBDV strains such as Gt, B87 and CEF94 in the cIBDV-like group, belonging to the Bla branch. The genotype of the YN-YX221110 isolate was A2dBla. [Conclusion] The broiler-derived IBDV isolate YN-YX221110 is successfully isolated, with segment A derived from nvIBDV and segment B from attIBDV in cIBDV-like strains, representing a novel reassorted IBDV strain. [ABSTRACT FROM AUTHOR]

The infectious bursal disease virus (IBDV) is a member of the viruses that can induce immunosuppression in chickens. In recent years, more and more IBDV-infected cases by the novel variant IBDV were reported in China, and it has been demonstrated that currently used vaccines could not provide complete protection against these new IBDV variants. However, a lack of comprehensive analysis of the genomic characteristics of the novel variant strain IBDV has hampered its vaccine development. In this study, a strain of IBDV, designated HB202201, was phylogenetically analyzed, and it was found that the hypervariable region (HVR) of VP2 belonged to the novel variant strain. Furthermore, the 5′- and 3′-ends of segments A and B were analyzed using the rapid amplification of cDNA end (RACE) method. After the full-length of segment A and segment B were determined, the phylogenetic analysis of the segment A and segment B showed that the isolated HB202201 belonged to A2dB1 genotype, which demonstrated the HB202201 belonged to the novel variant strain. In addition, the specific mutations in VP1-VP5 amino acids were analyzed, which showed that there were multiple typical mutations in novel variant IBDV proteins, including VP1 (G24, I141, V163, and E240), VP2 (K221, and I252), VP3 (Q167 and L196), and VP5 (R7, P44, R92, G104, and E147), whereas there was no typical mutation in VP4. This study provides insights into the genomic and antigenic characteristics of the novel variant IBDV, which will promote the development of novel vaccine against the novel variant IBDV.

Infectious bursal disease (IBD) is a highly epidemic and immunosuppressive disease of 3- to 6-week-old chicks caused by infectious bursal disease virus (IBDV). Since 2017, there has been a notable increase in the isolation rates of novel variant IBDV strains in China, of which characteristic amino acid residues were different from those of early antigen variants. In this study, one IBDV strain was isolated from a farm with suspected IBD outbreak in Shandong Province, China, which was designated LY21/2. The strain LY21/2 could replicate in MC38 cells with previous culture adaption in SPF chick embryos. Phylogenetic analysis revealed that LY21/2 formed one branch with novel variant IBDVs and shared 96.8–98.6% nucleotide sequence identity with them. Moreover, LY21/2 serving as the major parent underwent the recombination event of a variant strain (19D69), while the minor parent was a very virulent strain (Harbin-1). SPF chicks inoculated with LY21/2 showed no gross clinic symptom, whereas bursal atrophy was exhibited and apoptosis was occurred in 55.21% of bursal cells. The results of histopathology and immunohistochemical staining showed that lymphocyte depletion and connective tissue hyperplasia and IBDV antigen-positive cells were observed in the bursa of LY21/2-infected chicks. Besides, DNA fragmentation was detected in the LY21/2-infected bursal tissue section by TUNEL assay. Collectivtely, these data presented analysis and evaluation of the genetic characteristics and pathogenicity of a novel variant IBDV strain. This study may help in the development of biosafety strategies for the prevention and control of IBDV in poultry. [ABSTRACT FROM AUTHOR]

Infectious bursal disease (IBD) is caused by infectious bursal disease virus (IBDV), which has a genome consisting of two segments of double-stranded linear RNA. IBDVs have been traditionally divided into four phenotypes based on their pathogenicity and antigenicity, including classic, variant, very virulent, and attenuated IBDV. With the emergences of divergent molecular characteristics of novel strains produced by continuous mutations and recombination, it is increasingly difficult to define new IBDV strains using the traditional descriptive classification method. The most common classification scheme for IBDV with segmented genome is based solely on segment A, while the significance of segment B has been largely neglected. In this study, an improved scheme for IBDV genotype classification based on the molecular characteristics of both VP2 (a viral capsid protein encoded by segment A) and VP1 (an RNA-dependent RNA polymerase protein encoded by segment B) was proposed for the first time. In this scheme, IBDV was classified into nine genogroups of A and five genogroups of B, respectively; the genogroup A2 was further divided into four lineages. The commonly used phenotypic classifications of classic, variant, very virulent, and attenuated IBDVs correspond to the A1B1, A2B1, A3B2, and A8B1 genotypes of the proposed classification scheme. The novel variant IBDVs including the strains identified in this study were classified as belonging to genotype A2dB1. The flexibility and versatility of this improved classification scheme will allow the unambiguous identification of existing and emerging IBDV strains, which will greatly facilitate molecular epidemiology studies of IBDV.

Infectious bursal disease virus (IBDV) is a non-enveloped, bi-segmented double-stranded RNA virus and the causative agent of a poultry immunosuppressive disease known as infectious bursal disease (IBD). The novel variant IBDV (nVarIBDV) recently posed a great threat to the development of the poultry industry. In this study, we identified a novel segment-reassortant IBDV strain, IBDV-JS19-14701 (Genotype A2dB3). Phylogenic analysis showed that Segments A and B of IBDV-JS19-14701 were derived from emerging nVarIBDV (Genotype A2dB1) and long-prevalent HLJ0504-like strains (Genotype A3B3) in China, respectively. The pathogenicity of IBDV-JS19-14701 was further evaluated via animal experiments. IBDV-JS19-14701 exhibited a similar virulence to chickens with the nVarIBDV. The identification of this reassortment event is beneficial for understanding the epidemiology of nVarIBDV and will contribute to the efficient prevention and control of IBD.

The infectious bursal disease virus (IBDV) is a member of the viruses that can induce immunosuppression in chickens. In recent years, more and more IBDV-infected cases by the novel variant IBDV were reported in China, and it has been demonstrated that currently used vaccines could not provide complete protection against these new IBDV variants. However, a lack of comprehensive analysis of the genomic characteristics of the novel variant strain IBDV has hampered its vaccine development. In this study, a strain of IBDV, designated HB202201, was phylogenetically analyzed, and it was found that the hypervariable region (HVR) of VP2 belonged to the novel variant strain. Furthermore, the 5'- and 3'-ends of segments A and B were analyzed using the rapid amplification of cDNA end (RACE) method. After the full-length of segment A and segment B were determined, the phylogenetic analysis of the segment A and segment B showed that the isolated HB202201 belonged to A2dB1 genotype, which demonstrated the HB202201 belonged to the novel variant strain. In addition, the specific mutations in VP1-VP5 amino acids were analyzed, which showed that there were multiple typical mutations in novel variant IBDV proteins, including VP1 (G24, I141, V163, and E240), VP2 (K221, and I252), VP3 (Q167 and L196), and VP5 (R7, P44, R92, G104, and E147), whereas there was no typical mutation in VP4. This study provides insights into the genomic and antigenic characteristics of the novel variant IBDV, which will promote the development of novel vaccine against the novel variant IBDV., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Bo, Wang, Xu, Zhang, Guo, Cao, Zhang and Wu.)

Infectious bursal disease (IBD) is a highly epidemic and immunosuppressive disease of 3- to 6-week-old chicks caused by infectious bursal disease virus (IBDV). Since 2017, there has been a notable increase in the isolation rates of novel variant IBDV strains in China, of which characteristic amino acid residues were different from those of early antigen variants. In this study, one IBDV strain was isolated from a farm with suspected IBD outbreak in Shandong Province, China, which was designated LY21/2. The strain LY21/2 could replicate in MC38 cells with previous culture adaption in SPF chick embryos. Phylogenetic analysis revealed that LY21/2 formed one branch with novel variant IBDVs and shared 96.8-98.6% nucleotide sequence identity with them. Moreover, LY21/2 serving as the major parent underwent the recombination event of a variant strain (19D69), while the minor parent was a very virulent strain (Harbin-1). SPF chicks inoculated with LY21/2 showed no gross clinic symptom, whereas bursal atrophy was exhibited and apoptosis was occurred in 55.21% of bursal cells. The results of histopathology and immunohistochemical staining showed that lymphocyte depletion and connective tissue hyperplasia and IBDV antigen-positive cells were observed in the bursa of LY21/2-infected chicks. Besides, DNA fragmentation was detected in the LY21/2-infected bursal tissue section by TUNEL assay. Collectivtely, these data presented analysis and evaluation of the genetic characteristics and pathogenicity of a novel variant IBDV strain. This study may help in the development of biosafety strategies for the prevention and control of IBDV in poultry., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The reviewer KL declared a past collaboration with the authors to the handling editor at the time of review., (Copyright © 2023 Huang, Shu, Huang, Han, Li, Chen and Chen.)

Infectious bursal disease virus (IBDV) is a non-enveloped, bi-segmented double-stranded RNA virus and the causative agent of a poultry immunosuppressive disease known as infectious bursal disease (IBD). The novel variant IBDV (nVarIBDV) recently posed a great threat to the development of the poultry industry. In this study, we identified a novel segment-reassortant IBDV strain, IBDV-JS19-14701 (Genotype A2dB3). Phylogenic analysis showed that Segments A and B of IBDV-JS19-14701 were derived from emerging nVarIBDV (Genotype A2dB1) and long-prevalent HLJ0504-like strains (Genotype A3B3) in China, respectively. The pathogenicity of IBDV-JS19-14701 was further evaluated via animal experiments. IBDV-JS19-14701 exhibited a similar virulence to chickens with the nVarIBDV. The identification of this reassortment event is beneficial for understanding the epidemiology of nVarIBDV and will contribute to the efficient prevention and control of IBD. [ABSTRACT FROM AUTHOR]

• A recombinant IBDV between the novel variant and the intermediate vaccine strains was identified and named IBD16HeN01. • The homologous recombination resulted in increased pathogenicity of the novel variant IBDV strain to chick embryos. • IBD16HeN01 could induce severe bursal lesions in vivo. Infectious bursal disease virus (IBDV) is the causative agent of infectious bursal disease (IBD), an important immunosuppressive disease seriously threatening poultry farming worldwide. Since the identification of the classic strain in 1957, variant IBDV, very virulent IBDV, and novel variant IBDV have successively emerged brought severe challenges. Over the years, attenuated, intermediate, and intermediate-plus live vaccines have been developed to control the disease. The coexistence of various strains in flocks increases the probability of homologous recombination, and in this study, a naturally occurring homologous recombination between a novel variant strain and an intermediate vaccine strain of IBDV was first identified. Sequence analyses demonstrated that the IBD16HeN01 strain was a recombinant IBDV incorporating the skeleton of the novel variant IBDV (SHG19-like strain), where the 3′ region of segment A (nt 1539–3260) was replaced by an intermediate vaccine strain (W2512-like strain). Pathogenicity experiments indicated that IBD16HeN01 could cause severe bursal lesions and the recombination increased viral pathogenicity to chick embryos compared with the novel variant IBDV. Homologous recombination in IBDV has increased the complexity of disease prevention and control and reminds us that we should use live vaccines more scientifically and cautiously. [ABSTRACT FROM AUTHOR]