Comparative Pathogenicity of Malaysian variant and very virulent infectious bursal disease viruses in chickens

Novel variant infectious bursal disease virus diminishes FAdV-4 vaccination and enhances pathogenicity of FAdV-4

Infectious bursal disease virus (IBDV) caused an acute and highly contagious infectious disease characterized by severe immunosuppression, causing considerable economic losses to the poultry industry globally. Although this disease was well-controlled under the widely use of commercial vaccines in the past decades, the novel variant IBDV strains emerged recently because of the highly immunized-selection pressure in the field, posting new threats to poultry industry. Here, we reported novel variant IBDV is responsible for a disease outbreak, and assessed the epidemic and pathogenicity of IBDV in this study. Moreover, we constructed a challenge model using Fowl adenovirus serotype 4 (FAdV-4) to study on the immunosuppressive effect. Our findings underscore the importance of IBDV surveillance, and provide evidence for understanding the pathogenicity of IBDV.

The effect of ghrelin on bursa and cecal tonsils of chickens infected with an attenuated virus strain of infectious bursal disease virus

Infectious bursal disease (IBD) significantly affects the poultry industry, causing substantial economic losses. This study aimed to investigate the effects of ghrelin on chicks infected with an attenuated virus strain of IBDV (aIBDV). Chicks were divided into 3 groups: a control group (group I), an aIBDV infection group (group II), and a ghrelin + aIBDV infection group (group III). Mice in groups II and III were fed until they reached 19 d of age and then inoculated with aIBDV to establish a subclinical infection model. Group III received an intraperitoneal injection of 0.5 nmol/100 g ghrelin from d 17 to 23. The present study utilized paraffin sectioning, H&E staining, and immunohistochemical staining to examine the effects of ghrelin on the bursa of fabricius and cecum tonsils in aIBDV-infected chicks. The results indicated that at 3 d postinfection (dpi), the average body weight of group III was significantly greater than that of group II (P < 0.05). At 3 and 7 dpi, the proportion of large lymphoid follicles in the bursa of fabricius in group III was notably greater than that in group II (P < 0.05). aIBDV infection resulted in bleeding, edema, and fibrosis in the cecal mucosal layer of chicks, but ghrelin administration mitigated these pathological changes. At 3 and 7 dpi, the thickness of the lamina propria in the cecal tonsils of group III was significantly lower than that in the cecal tonsils of group II (P < 0.05). Additionally, the percentage of large lymphoid follicles in the cecal tonsils of group III was significantly greater than that in group II at 3 and 5 dpi (P < 0.05). There were significantly fewer macrophages in the cecal tonsils of group III than in those of group II at 1, 3, and 5 dpi (P < 0.05). In conclusion, ghrelin supplementation improved performance and mitigated bursal atrophy in aIBDV-infected chicks. It also reduced histological lesions and immune responses in the cecum tonsil. Notably, the reduction in macrophages in the cecum tonsil following ghrelin administration may decrease the risk of aIBDV spread.

Characterization and pathogenicity of a novel variant infectious bursal disease virus in China

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.

Host Combats IBDV Infection at Both Protein and RNA Levels

Infectious bursal disease (IBD) is an acute, highly contagious, and immunosuppressive avian disease caused by infectious bursal disease virus (IBDV). In recent years, with the emergence of IBDV variants and recombinant strains, IBDV still threatens the poultry industry worldwide. It seems that the battle between host and IBDV will never end. Thus, it is urgent to develop a more comprehensive and effective strategy for the control of this disease. A better understanding of the mechanisms underlying virus-host interactions would be of help in the development of novel vaccines. Recently, much progress has been made in the understanding of the host response against IBDV infection. If the battle between host and IBDV at the protein level is considered the front line, at the RNA level, it can be taken as a hidden line. The host combats IBDV infection at both the front and hidden lines. Therefore, this review focuses on our current understanding of the host response to IBDV infection at both the protein and RNA levels.

The Over-40-Years-Epidemic of Infectious Bursal Disease Virus in China

Infectious bursal disease (IBD) is an acute, highly contagious, immunosuppressive disease of chickens caused by the virus (IBDV), which critically threatens the development of the global chicken industry and causes huge economic losses. As a large country in the poultry industry, the epidemic history of IBDV in China for more than 40 years has been briefly discussed and summarized for the first time in this report. The first classic strain of IBDV appeared in China in the late 1970s. In the late 1980s and early 1990s, the very virulent IBDV (vvIBDV) rapidly swept across the entirety of China, threatening the healthy development of the poultry industry for more than 30 years. Variants of IBDV, after long-term latent circulation with the accumulation of mutations since the early 1990s, suddenly reappeared as novel variant strains (nVarIBDV) in China in the mid-2010s. Currently, there is a coexistence of various IBDV genotypes; the newly emerging nVarIBDV of A2dB1 and persistently circulating vvIBDV of A3B3 are the two predominant epidemic strains endangering the poultry industry. Continuous epidemiological testing and the development of new prevention and control agents are important and require more attention. This report is of great significance to scientific cognition and the comprehensive prevention and control of the IBDV epidemic.

Dynamics of the Emerging Genogroup of Infectious Bursal Disease Virus Infection in Broiler Farms in South Korea: A Nationwide Study

Infectious bursal disease (IBD), caused by IBD virus (IBDV), threatens the health of the poultry industry. Recently, a subtype of genogroup (G) 2 IBDV named G2d has brought a new threat to the poultry industry. To determine the current status of IBDV prevalence in South Korea, active IBDV surveillance on 167 randomly selected broiler farms in South Korea from August 2020 to July 2021 was conducted. The bursas of Fabricius from five chickens from each farm were independently pooled and screened for IBDV using virus-specific RT-PCR. As a result, 86 farms were found to be infected with the G2d variant, 13 farms with G2b, and 2 farms with G3. Current prevalence estimation of IBDV infection in South Korea was determined as 17.8% at the animal level using pooled sampling methods. G2d IBDV was predominant compared to other genogroups, with a potentially high-risk G2d infection area in southwestern South Korea. The impact of IBDV infection on poultry productivity or Escherichia coli infection susceptibility was also confirmed. A comparative pathogenicity test indicated that G2d IBDV caused severe and persistent damage to infected chickens compared with G2b. This study highlights the importance of implementation of regular surveillance programs and poses challenges for the comprehensive prevention of IBDV infections.

Analysis of the global origin, evolution and transmission dynamics of the emerging novel variant IBDV (A2dB1b): The accumulation of critical aa-residue mutations and commercial trade contributes to the emergence and transmission of novel variants

The Chinese IBDV novel variant (nvIBDV), belonging to the genotype A2dB1b, an emerging pathotype that can cause subclinical disease with severe, prolonged immunosuppression, poses a new threat to the poultry industry. The process of the global origin, evolution and transmission dynamics of nvIBDV, however, is poorly understood. In this study, phylogenetic trees, site substitutions of amino acid (aa) and highly accurate protein structure modelling, selection pressure, evolutionary and transmission dynamics of nvIBDV were analysed. Interestingly, nvIBDV was classified into the same genogroup with the early US antigenic variants (avIBDV) but in a new lineage with a markedly different and specific pattern of 17 aa-residual substitutions: 13 in VP2 (77D, 213N, 221K, 222T, 249K, 252I, 253Q, 254N, 284A, 286I, 299S, 318D and 323E) and four in VP1 (141I, 163V, 240E and 508K). Importantly, the aa-residues 299S and 163V may play a key role in cell binding and polymerase activity, respectively. The effective population size of the circulating avIBDV experienced two growth phases, respectively, in the years 1999-2007 (in North America) and 2015-2021 (in Asia), which is consistent with the observed trend of the epidemic outbreaks. The most recent common ancestor (tMRCA) of avIBDV most first originated in the USA and was dated around the 1970s. After its emergence, the ancestor virus of this group probably spread to China around the 1990s and the variants experienced a long-term latent circulation with the accumulation of several critical aa-residue mutations in VP2 until re-emerging in 2016. At present, central China has become the epicentre of nvIBDV spread to other parts of China and Asian countries. Importantly, a strong correlation seems to exist between the transmission patterns of virus and the flow of commercial trade of live poultry and products. These findings provide important insights into the origin, evolution and transmission of the nvIBDV and will assist in the development of programs for control strategies for these emerging viruses.