Infectious bursal disease virus in chickens: prevalence, impact, and management strategies

Very virulent infectious bursal disease virus infection triggered microscopic changes, apoptosis, and inflammatory cytokines imbalance in chicken spleen and thymus

AbstractInfectious bursal disease virus (IBDV) can cause a highly contagious disease, resulting in severe damage to the immune system that causes immunosuppression in young chickens. Both spleen and thymus are important immune organs, which play a key role in eliciting protective immune responses. However, the effects of very virulent IBDV (vvIBDV) strain LJ-5 infection on chicken spleen and thymus are still unknown. In the present study, three-week-old specific pathogen-free (SPF) chickens were infected with vvIBDV for one to five days. The vvIBDV infection significantly increased the spleen index and decreased the thymus index.Microscopic analysis indicated necrosis, depletion of the lymphoid cells and complete loss of structural integrity in spleen and thymus. Ultrastructural analysis displayed mitochondrial and nuclear damage, including mitochondrial cristae breaks, and deformation of nuclear membrane in vvIBDV-infected spleen and thymus tissues. Cytokine levels increased in the spleen and thymus after IBDV infection, promoting inflammation and causing an inflammatory imbalance. Moreover, the mRNA expression of apoptosis-related genes was significantly upregulated in the vvIBDV infection group compared to in the control group. Meanwhile, the mRNA expression of mitochondrial dynamics was altered in the spleen and thymus of vvIBDV-infected chickens. These results suggested that vvIBDV infection triggers an imbalance of inflammatory cytokines, and apoptosis in the spleen and thymus, resulting in immune injury in chickens. This study offered basic data for the further study of vvIBDV pathogenesis.

Generation of a novel attenuated IBDV vaccine strain by mutation of critical amino acids in IBDV VP5

Infectious bursal disease virus (IBDV) is an acute and highly infectious RNA virus known for its immunosuppressive capabilities, chiefly inflicting rapid damage to the bursa of Fabricius (BF) of chickens. Current clinical control of IBDV infection relies on vaccination. However, the emergence of novel variant IBDV (nVarIBDV) has posed a threat to the poultry industry across the globe, underscoring the great demand for innovative and effective vaccines. Our previous studies have highlighted the critical role of IBDV VP5 as an apoptosis-inducer in host cells. In this study, we engineered IBDV mutants via a reverse genetic system to introduce amino acid mutations in VP5. We found that the mutant IBDV-VP5/3m strain caused reduced host cell mortality, and that strategic mutations in VP5 reduced IBDV replication early after infection, thereby delaying cell death. Furthermore, inoculation of chickens with IBDV-VP5/3m effectively reduced damage to BF and induced neutralizing antibody production comparable to that of parental IBDV WT strain. Importantly, vaccination with IBDV-VP5/3m protected chickens against challenges with nVarIBDV, an emerging IBDV variant strain in China, reducing nVarIBDV loads in BF while alleviating bursal atrophy and splenomegaly, suggesting that IBDV-VP5/3m might serve as a novel vaccine candidate that could be further developed as an effective vaccine for clinical control of IBD. This study provides a new clue to the development of novel and effective vaccines.

Genetic Sequence and Pathogenicity of Infectious Bursal Disease Virus in Chickens in Egypt During 2017-2021

The continued circulation of infectious bursal disease virus (IBDV) in Egypt, despite the use of various vaccines, is a serious problem that requires continuous detection of IBDV. In the current study, real-time reverse transcriptase polymerase chain reaction testing of 100 diseased chicken flocks during 2017-2021 revealed the presence of very virulent IBDV (vvIBDV) in 67% of the flocks, non-vvIBDV in 11%, and a mixture of both vvIBDV and non-vvIBDV in 4%. Twenty-nine IBDV isolates were submitted for partial sequencing of the viral protein 2 hypervariable region (VP2-HVR), and 27 isolates were confirmed to be genogroup A3 (vvIBDV) with 96.3%-98.5% similarity to the global A3 (vvIBDV) and 88.9%-97% similarity to genogroup A1 vaccine strains. The remaining two isolates were non-vvIBDV and showed 91.1% and 100% identity with classical genogroup A1 strains, respectively. Furthermore, the sequence and phylogenetic analysis of VP1 (amino acids 33-254) of two selected isolates of A3, 5/2017 and 98/2021, clustered them as B2, vvIBDV-like, strains with high similarity (99.5%) to four Egyptian, 99% to Chinese and European, and 97.7% to Chinese and Polish vvIBDV isolates. Experimental infection of commercial broiler chickens with two vvIBDV-A3B2 isolates (5/2017 and 98/2021) showed no mortality despite typical tissue lesions, clear histopathological changes, and strong ELISA antibody response. Isolate 98/2021 was more pathogenic, as confirmed by histopathology, whereas isolate 5/2017 induced a stronger serological response. In conclusion, vvIBDV (A3B2) strains with two amino acid (aa) substitutions in VP1 as V141I and V234I as well as VP2 as Y220F and G254S are still circulating in Egypt.

Effects of ultra-filtration purification of infectious bursal disease virus on immune responses and cytokine activation in specific pathogen free chickens

Purification is an important step in the production of viral vaccines that strongly affects product recovery and subsequent immune responses. The present study was carried out with the aim of improving the purification of infectious bursal disease virus (IBDV) by the tangential flow filtration (TFF) method. Then, the effect of the purified virus on the induction of immune responses against IBDV in specific pathogen free (SPF) chickens was investigated. The IBD07IR strain was propagated in embryonated SPF eggs. The virus was purified using a 100 kDa cassette. The quality of the recovered viruses was evaluated by titration. A total number of 60 SPF chickens were randomly divided into three groups (n = 20) and received the concentrated viral antigen, commercial live IBDV vaccine and phosphate-buffered saline at the age of 3 weeks by eye drop method. The bursa of Fabricius was examined histopathologically for possible changes. Sera were collected at 1-week intervals from day 0 until the end of 6 weeks after vaccination. The IBDV-specific antibody levels, induction of cell-mediated immunity and mRNA expression levels of cytokines were evaluated. The results showed that despite a relative raise in virus titer from 7.66 to 8.17 embryo infectious dose (EID)50 mL-1 following purification, both the purified IBDV and commercial vaccine are able to induce strong immune responses against the virus. Within a context of egg-based IBDV vaccine production, a single-step TFF can be applied for the relatively purification. This platform requires a further study in the selection of multiple membranes to optimize the operating conditions and final product.

Isolation and genomic characteristics of the novel variant infectious bursal disease virus in China

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.

The effect of micronutrient supplementation on bioavailability, antioxidants activity, and weight gain in response to Infectious Bursal Disease vaccination in commercial broilers

The effect of supplementing organic selenium and zinc on bioavailability, oxidative stress, weight gain in commercial broilers was studied. A total of 180-day-old chicks were divided into six groups: NSUV (Not supplemented, unvaccinated), NSV (Not supplemented, vaccinated), VS (vaccinated, supplemented selenium), VZ (vaccinated supplemented zinc), VSZ (vaccinated supplemented selenium and zinc), UVSZ (unvaccinated supplemented selenium and zinc). 1 mg/kg selenium and 60 mg/kg zinc were added to the feed of supplemented groups. The concentration of selenium (0.05 ± 0.00 mg/L) in VS and zinc (0.66 ± 0.13 mg/L) in VZ were lower on day 27 post-vaccination compared to day 10 (VS= 0.07 ± 0.01 mg/L; VZ= 1.46 ± 0.30 mg/L). Glutathione peroxidase and catalase concentrations were highest in the supplemented groups compared to unsupplemented groups on day 27 post vaccination, expressing a similar trend with the micronutrients. There was no difference (P ≥ 0.05) in the glutathione concentration between all groups except on day 27 post vaccination where SZV group was significantly higher (P=0.02) compared to the NSV group. Catalase concentration was significantly decreased in the NSV group compared to SZV (P=0.04) on day 27 post vaccination. The NSV group (1.64 ± 0.13 kg) weighed significantly lower (P=0.02) than the VSZ (2.00 ± 0.12 kg) in the fifth week, while on the sixth week, the SZV group gained the highest weight (2.04 ± 0.18 kg). The supplementation of organic selenium and zinc in broilers increased the serum micronutrients bioavailability, decreased oxidative stress, increased weight gain, thus, enhancing immunity in the broilers.

Ribavirin inhibits the replication of infectious bursal disease virus predominantly through depletion of cellular guanosine pool

Introduction

The antiviral activity of different mutagens against single-stranded RNA viruses is well documented; however, their activity on the replication of double-stranded RNA viruses remains unexplored. This study aims to investigate the effect of different antivirals on the replication of a chicken embryo fibroblast-adapted Infectious Bursal Disease virus, FVSKG2. This study further explores the antiviral mechanism utilized by the most effective anti-IBDV agent.

Methods

The cytotoxicity and anti-FVSKG2 activity of different antiviral agents (ribavirin, 5-fluorouracil, 5-azacytidine, and amiloride) were evaluated. The virus was serially passaged in chicken embryo fibroblasts 11 times at sub-cytotoxic concentrations of ribavirin, 5-fluorouracil or amiloride. Further, the possible mutagenic and non-mutagenic mechanisms utilized by the most effective anti-FVSKG2 agent were explored.

Results and Discussion

Ribavirin was the least cytotoxic on chicken embryo fibroblasts, followed by 5-fluorouracil, amiloride and 5-azacytidine. Ribavirin inhibited the replication of FVSKG2 in chicken embryo fibroblasts significantly at concentrations as low as 0.05 mM. The extinction of FVSKG2 was achieved during serial passage of the virus in chicken embryo fibroblasts at ≥0.05 mM ribavirin; however, the emergence of a mutagen-resistant virus was not observed until the eleventh passage. Further, no mutation was observed in 1,898 nucleotides of the FVSKG2 following its five passages in chicken embryo fibroblasts in the presence of 0.025 mM ribavirin. Ribavarin inhibited the FVSKG2 replication in chicken embryo fibroblasts primarily through IMPDH-mediated depletion of the Guanosine Triphosphate pool of cells. However, other mechanisms like ribavirin-mediated cytokine induction or possible inhibition of viral RNA-dependent RNA polymerase through its interaction with the enzyme's active sites enhance the anti-IBDV effect. Ribavirin inhibits ds- RNA viruses, likely through IMPDH inhibition and not mutagenesis. The inhibitory effect may, however, be augmented by other non-mutagenic mechanisms, like induction of antiviral cytokines in chicken embryo fibroblasts or interaction of ribavirin with the active sites of RNA-dependent RNA polymerase of the virus.

Genetic Insight into the Interaction of IBDV with Host-A Clue to the Development of Novel IBDV Vaccines

Infectious bursal disease virus (IBDV) is an immunosuppressive pathogen causing enormous economic losses to the poultry industry across the globe. As a double-stranded RNA virus, IBDV undergoes genetic mutation or recombination in replication during circulation among flocks, leading to the generation and spread of variant or recombinant strains. In particular, the recent emergence of variant IBDV causes severe immunosuppression in chickens, affecting the efficacy of other vaccines. It seems that the genetic mutation of IBDV during the battle against host response is an effective strategy to help itself to survive. Therefore, a comprehensive understanding of the viral genome diversity will definitely help to develop effective measures for prevention and control of infectious bursal disease (IBD). In recent years, considerable progress has been made in understanding the relation of genetic mutation and genomic recombination of IBDV to its pathogenesis using the reverse genetic technique. Therefore, this review focuses on our current genetic insight into the IBDV's genetic typing and viral genomic variation.

Examination of macroscopic and microscopic lesions in IBDV-infected organs and molecular characterization of IBDV VP1 gene fragments obtained from commercial broiler farms in Indonesia

Background and Aim

Infectious bursal disease (IBD) is an infectious immunosuppressive disease that affects young chickens. Instead of strict biosecurity practices, vaccination is used to control IBD. However, the disease has not been effectively managed. Variations in the observed clinical symptoms lead to confounding diagnoses. The study aimed to obtain pathological lesion data from chickens suspected of IBD virus (IBDV) infection by gross pathology, confirm IBDV infection through molecular diagnostics, and genotype the VP1 gene fragments of circulating IBDV in the field.

Materials and Methods

The bursa of Fabricius, thymus, spleen, proventricular-ventricular junction, thigh muscles, and kidneys samples were collected from chickens suspected of IBDV infection from four commercial broiler farms in Central Java and The Yogyakarta Special Region Province between 2021 and 2022. The collected samples were examined histopathologically. Infectious bursal disease virus RNA was extracted from the bursa of Fabricius and VP1 gene was identified by reverse-transcriptase polimerase chain reaction (RT-PCR). The RT-PCR positive sample were sequenced and analyzed in Mega X for homology search and phylogenetic tree analysis.

Results

Macroscopic pathological lesions in the bursa of Fabricius were demonstrated by enlarged edema and thickened plica, presence of gelatinous exudate, hemorrhage, atrophy, and caseous exudate in the lumen. Moreover, the thymus had atrophy and small gray foci were observed in the spleen. Petechiae or hemorrhage was detected on the thigh muscle, and the kidney was dull and pale. Hemorrhage in the proventricular-ventricular junction was distinct. The histopathological examination of the bursa of Fabricius showed follicular vacuolization, edema, heterophilic infiltration, follicular atrophy, congestion, and hemorrhage. The thymus and spleen showed the presence of multifocal necrosis. Hemorrhage was observed in thigh muscle and mucosal part of proventricular-ventricular junction. Vacuolization was seen in renal tubules (nephrosis). Reverse transcriptase-PCR of 26 bursa of Fabricius samples from chickens suspected of IBDV infection showed four negative and 22 positive samples. Phylogenetic analysis of the VP1 gene fragment has indicated very virulent IBD (vvIBD) and belonged to B2 genotype.

Conclusion

Infectious bursal diseases virus infection in broiler chicken generated macroscopic and microscopic primary lesions in the bursa of Fabricius and thigh muscle. Other organs such as the spleen, thymus, proventricular-ventricular junction, and kidney, were also involved. Molecular analysis of the VP1 gene confirmed the causative agent and grouped the virus into vvIBD and B2 genotype. All samples were collected from vaccinated birds therefore, the efficacy of available vaccine is required for urgent evaluation. Since most studies only focused on VP1, further exploration on VP2 gene is suggested notably for new-generation vaccines. Monitoring clinical signs' transformation over time could assist field diagnostics.

Isolation and molecular characterization of infectious bursal disease virus circulating in western and central India

Background

Infectious bursal disease (IBD) caused substantial economic loss in central and western India during 2020 and 2021.

Aims

The study was conducted to characterize IBD virus (IBDV) from field outbreaks.

Methods

The study was conducted on 360 samples from 42 poultry flocks. The samples were subjected to histopathology and molecular detection, followed by phylogenetic typing of the partial VP2 gene.

Results

The mortality ranged from 15.25 to 60.18%. The necropsy showed hemorrhages on thigh muscles, mottled spleen, swelling of kidneys and bursae with hemorrhages, and cheesy exudate. Histopathology revealed extensive necrosis and depletion of follicular lymphoid cells within the cortex and medulla, along with widespread hemorrhages, edema, and cystic cavities in the bursa. The field isolates showed cytopathic effects in the seventh passage. The cytopathic effects included swelling, rounding, granulation of cytoplasm around the nucleus, fragmentation of the infected cells, and detachment. The reverse transcription-polymerase chain reaction amplified 664 bp partial VP2 gene. The phylogenetic analysis identified 19 field isolates as very virulent IBDVs (vvIBDVs) and three as classical strains.

Conclusion

The results indicated that different vvIBDV strains are involved in disease outbreaks in central and western India.

Cyto- and histoarchitectonics of the chicken spleen in the post-vaccination period

One of the main functions of the spleen is participation in many immunological processes, protecting the body from various harmful agents. It is a secondary organ of lymphopoiesis and the only organ of immunogenesis, which provides immune control of blood and detects genetically foreign agents in it, and performs the role of a biological filter. Therefore, the Study of its histo-architectonics has theoretical and practical significance. The histostructure of the spleen of chickens has significant differences, particularly the absence of trabeculae, a small amount of connective tissue based around large vessels. The structure of the spleen of one-day-old vaccinated and non-vaccinated chickens is not formed, as there is no differentiation of the white pulp from the red pulp, which is related to the biological features of the chickens' body. According to our research, the presence of lymphoid nodules is observed for the first time in the 25-day age of the vaccinated group chickens. According to morphometric studies, it was established that their number was 2.33 ± 0.42 pcs. Comprehensive farm vaccination programs include ten vaccinations of chickens up to 100 days of age. Under the influence of multiple antigenic stimulations in the following age periods of a 50-day-old bird (after six vaccinations: twice against infectious bronchitis and infectious bursal disease, once against Marek's disease and Newcastle disease), the 75-day (after nine times vaccination), 100-day (after ten times vaccination) number and sizes of lymphoid nodules, as well as periarterial lymphoid sheaths and periellipsoid lymphoid sheaths increased concerning chickens of the control group. Our research established that the histostructure of the spleen of one-day-old chickens of the experimental and control groups is incomplete. The bird's spleen, a peripheral organ of immune protection, is formed at 25 days. However, chickens are vaccinated twice (against Marek's disease and infectious bronchitis) in the incubator when they are less than one day old, and 90% of the planned vaccinations are completed by the age of 75 days. Therefore, studying morphological changes in the spleen of birds of different ages can be an essential tool for re-evaluating preventive treatment protocols in modern poultry farming.

Broad Antiviral Spectrum of Glycyrrhizic Acid for Human and Veterinary Medicine: Reality or Fiction?

BACKGROUND

Emerging virus infections provoke health problems in people and animals, which generate social and economic issues worldwide. This has spurred the search for new pharmacological strategies to confront them.

SUMMARY

The purpose of this review is to draw the reader's attention to pharmacological evaluations of glycyrrhizic acid (GA) and its analogs on the broad range of viruses known in human and veterinary medicine. GA is the main water-soluble constituent extracted from the roots of plants from the genus Glycyrrhiza, commonly known as licorice root. It has long been used due to its broad spectrum of bioactivities, including anti-inflammatory, antiulcer, and antitumor properties. It has also been proposed as an antiviral agent. Medicines derived from GA are currently being used to combat acute and chronic hepatitis and herpes viruses.

KEY MESSAGES

This review suggests that GA could be a new broad-spectrum antiviral due to its ability to inhibit DNA or RNA viruses both in vitro and in vivo. GA could be a potential drug for preventing and/or treating various viral diseases.

Comparative Study of the Immune Response Induced by an Argentinian Classical Strain of IBDV in Two Chicken Breeds

The hybrid chicken Negra INTA, which originated at the National Institute of Agricultural Technology (INTA), is the product of the cross between Barred Plymouth Rock females and Rhode Island Red males, and it is used as a laying hen for egg consumption. It has been characterized by productive parameters, but the characterization from an immunological perspective has not been done yet. Infectious bursal disease virus (IBDV) causes a highly contagious viral disease that affects the bursa of Fabricius. Although most chickens are regularly vaccinated against IBDV, this virus still generates negative impacts on production with significant economic losses. The aim of the present work was to compare the immune responses of the Negra INTA hybrid and the White Leghorn layer line to the infection with a field isolate of IBDV. Four-week-old chickens were infected with a single dose of IBDV and at 3, 5, 7, and 30 days postinfection (dpi), bursae were removed, and different parameters were evaluated. Results showed that the reduction of the bursa body (BB) ratio and the histopathological damage were maximum on day 7 postinfection (pi). The viral load was greater in the hybrid Negra INTA at 5 dpi. The humoral immune response between both breeds was similar, although more animals from the commercial line showed higher titers of neutralizing antibodies. Flow cytometry analysis revealed that Bu+ bursal lymphocytes reached a minimum at 7 dpi. Meanwhile, T cell infiltration measured by the percentage of CD3+, CD4+, and CD8+ cells in the bursa was at its maximum at 5 dpi. To our knowledge, this work describes for the first time the pathogenesis and the immune response caused by an Argentinian IBDV isolate in two different chicken lines.

Flagellin Improves the Immune Response of an Infectious Bursal Disease Virus (IBDV) Subunit Vaccine

Flagellin activates the immune system through Toll-like receptor 5 (TLR5) and can work as an adjuvant for subunit vaccines. In this study, we tested the adjuvancy of two different N-terminal fragments of flagellin, (1) FliC99, residues 1–99, and (2) FliC176, residues 1–176, to incorporate larger areas of the hotspot region for potentially higher levels of TLR5 activation and immune response. A truncated version of the VP2 protein (name tVP2, residues 199–356) of the Infectious bursal disease virus (IBDV) was genetically linked to the flagellin constructs, and the immune response was evaluated in chickens. Results showed that both chimeric antigen–adjuvant constructs increased humoral (total IgG titers), cellular and cytokine immune response (IL-4, IFN-γ). The resulting antibody also successfully neutralized IBDV. We conclude that the N-terminus of flagellin can act as an immune activator to enhance vaccine efficacy.

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.

A Cross-Sectional Seroepidemiological Study on Infectious Bursal Disease in Backyard Chickens in the Mymensingh District of Bangladesh

Infectious bursal disease (IBD) is a highly contagious disease that causes significant economic loss in chickens. A cross-sectional study was conducted in the Mymensingh district of Bangladesh to determine the seroprevalence of IBD virus (IBDV) antibodies in backyard chickens and their association with different epidemiological risk factors. A total of 460 serum samples were randomly collected from backyard chickens that had not been previously vaccinated against IBDV. The collected sera were examined using an enzyme-linked immunosorbent assay (ELISA). Data on epidemiological risk factors were collected through face-to-face interviews with owners and subjected to both uni- and multivariable risk analyses to determine their association with IBDV infection. Using ELISA, the overall seroprevalence of IBDV antibodies in backyard chickens was 83.4% (95% confidence interval: 79.8%–86.6%), among which, a significantly higher seroprevalence was recorded in females (83.4%, 345/350), 4–6 weeks age group (95.3%, 244/256), and unhealthy (95.0%, 57/60) backyard chickens than those of males, other age groups, and healthy chickens, respectively. Furthermore, chickens reared in free-ranging housing systems (93.3%, 280/300) and poor-conditioned houses (98.0%, 147/150) showed a significantly higher seropositivity of IBDV antibodies than those reared in separated housing systems and other hygienic-conditioned houses, respectively. Moreover, compared with their counterparts, a higher but nonsignificant seroprevalence of IBDV antibodies was observed in backyard chickens that were selected from Fulbaria Upazila (88.8%; 80/90) and which were brought from the marketplace (85.7%, 60/70). A higher seropositivity of IBDV antibodies was shown to be statistically associated with various critical epidemiological risk factors, indicating that field strains of IBDV were exposed in backyard chickens and could be readily transferred horizontally. Proper prevention and control methods, villagers' awareness of IBD, and the rapid and widespread use of seroepidemiological investigations could help to reduce the spread of IBDV infection in backyard chickens.

Concurrent Occurrence of Infectious Bursal Disease and Multicausal Respiratory Infections Caused by Newcastle Disease and Avian Metapneumovirus in Broilers

Control strategy of respiratory complex infections should address precipitating and predisposing causative agents in general and immunosuppressive agents in particular. In both clinical and subclinical forms, infectious bursal disease virus (IBDV) is one of the most immunosuppressive diseases of young chickens. This study aimed to investigate the concurrent occurrence of subclinical infectious bursal disease (IBD) and multicausal respiratory complex infections caused by Newcastle disease virus (NDV) and avian metapneumovirus (aMPV) in broilers. In this study, 800 tissue samples (e.g., trachea, cecal tonsil, bursa of Fabricius, and spleen) and 400 sera samples were collected from broilers with confirmed respiratory signs selected from 20 broiler farms in west Azerbaijan province, Iran, from October 2018 to February 2019. Pathogens in the tissue samples were detected using RT-PCR for the VP2 gene of IBDV, F gen of NDV, and N gene of aMPV. The amplified products were sequenced afterward. At the end of the husbandry period, sera samples were used to detect antibodies against IBDV, aMPV, and NDV using ELISA and HI tests. Molecular results showed that the 45% (9/20), 30% (6/20), and 15% (3/20) of tissue samples were positive for IBDV, NDV, and aMPV, respectively. Regarding co-infection, 5% (1/20) of farm isolates were positive for IBD and ND, while 10% (2/20) of farms isolates were positive for IBD and aMPV. Co-infection of IBD, ND, and aMPV was not detected in farm isolates. Serological results indicated that the IBD co-infected flocks had almost higher (P<0.05) antibody titers against IBD; however, IBDV-NDV co-infected flocks and IBDV-aMPV co-infected flocks had lower antibody titer against NDVand aMPV, respectively. It can be concluded that lower antibody titer against ND and aMPV in IBD-ND and IBD-aMPV co-infections indicated suppressive effects of IBD on these diseases. Therefore, vaccination against IBD even in regions without clinical form of IBD is inevitable for the reduction of immunosuppressive effects of subclinical IBD on immune responses against these diseases.

An Improved, Dual-Direction, Promoter-Driven, Reverse Genetics System for the Infectious Bursal Disease Virus (IBDV)

The infectious bursal disease virus (IBDV), one member of the Birnaviridae family, causes immunosuppression in young chickens by damaging the mature B cells of the bursa of Fabricius (BF), the central immune system of young chickens. The genome of IBDV is a bisegmented, double-strand RNA (dsRNA). Reverse genetics systems for IBDV allow the generation of genetically manipulated infectious virus via transfected plasmid DNA, encoding the two genomic viral RNA segments as well as major viral proteins. For this purpose, the minus-sense of both segment A and segment B are inserted into vectors between the polymerase I promoter and the corresponding terminator I. These plasmids facilitate the transcription of the viral minus-sense genome but copy the plus-sense genome as well viral protein translation depends on the activity of VP1 and VP3, when transfected into 293T cells. To further improve rescue efficiency, dual-direction promoters were generated based on the polymerase II promoter in the reverse direction in the backbone of the pCDNA3.0 vector. Therefore, the polymerase I promoter transcribes the viral minus-sense genome in the forward direction and the polymerase II promoter transcribes viral mRNA, translated into viral proteins that produce infectious IBDV. We also found that the rescue efficiency of transfecting two plasmids is significantly higher than that of transfecting four plasmids. In addition, this dual-direction promoter rescue system was used to generate R186A mutant IBDV since Arg186 is the arginine monomer-methylation site identified by LC–MS. Our data furtherly showed that the Arg186 monomer methylation mutant was due to a reduction in VP1 polymerase activity as well as virus replication, suggesting that the Arg186 methylation site is essential for IBDV replication.

Vaccines against Major Poultry Viral Diseases: Strategies to Improve the Breadth and Protective Efficacy

The poultry industry is the largest source of meat and eggs for human consumption worldwide. However, viral outbreaks in farmed stock are a common occurrence and a major source of concern for the industry. Mortality and morbidity resulting from an outbreak can cause significant economic losses with subsequent detrimental impacts on the global food supply chain. Mass vaccination is one of the main strategies for controlling and preventing viral infection in poultry. The development of broadly protective vaccines against avian viral diseases will alleviate selection pressure on field virus strains and simplify vaccination regimens for commercial farms with overall savings in husbandry costs. With the increasing number of emerging and re-emerging viral infectious diseases in the poultry industry, there is an urgent need to understand the strategies for broadening the protective efficacy of the vaccines against distinct viral strains. The current review provides an overview of viral vaccines and vaccination regimens available for common avian viral infections, and strategies for developing safer and more efficacious viral vaccines for poultry.

A comprehensive review of viruses in terrestrial animals from the Caribbean islands of Greater and Lesser Antilles

Viruses pose a major threat to animal health worldwide, causing significant mortalities and morbidities in livestock, companion animals and wildlife, with adverse implications on human health, livelihoods, food safety and security, regional/national economies, and biodiversity. The Greater and Lesser Antilles consist of a cluster of islands between the North and South Americas and is habitat to a wide variety of animal species. This review is the first to put together decades of information on different viruses circulating in companion animals, livestock, and wildlife from the Caribbean islands of Greater and Lesser Antilles. Although animal viral diseases have been documented in the Caribbean region since the 1940s, we found that studies on different animal viruses are limited, inconsistent, and scattered. Furthermore, a significant number of the reports were based on serological assays, yielding preliminary data. The available information was assessed to identify knowledge gaps and limitations, and accordingly, recommendations were made, with the overall goal to improve animal health and production, and combat zoonoses in the region. This article is protected by copyright. All rights reserved.

Virulence of Emerging Arthrotropic Avian Reoviruses Correlates With Their Ability to Activate and Traffic Interferon-γ Producing Cytotoxic CD8+ T Cells Into Gastrocnemius Tendon

Newly emerging arthrotropic avian reoviruses (ARVs) are genetically divergent, antigenically heterogeneous, and economically costly. Nevertheless, the mechanism of emerging ARV-induced disease pathogenesis and potential differences in virulence between virus genotypes have not been adequately addressed. In this study, the life cycle of ARV, including the formation of cytoplasmic ARV neo-organelles, paracrystalline structures, and virus release mechanisms, were characterized in the infected host cell by transmission electron microscopy (TEM). In addition, progressive changes in the structure of infected cells were investigated by time-lapse and field emission scanning electron (FE-SE) microscopy. ARVs from the four genotypic cluster groups included in the study caused gross and microscopic lesions in the infected birds. Marked infiltration of γδT cells, CD4⁺ and CD8⁺ T lymphocytes were observed in ARV infected tendon tissues starting day 3 post-infection. The ARV variant from genotype cluster-2 triggered significantly high trafficking of IFN-γ producing CD8⁺ T lymphocytes in tendon tissues and concomitantly showed high morbidity and severe disease manifestations. In contrast, the ARV variant from genotype cluster-4 was less virulent, caused milder disease, and accompanied less infiltration of IFN-γ producing CD8⁺ T cells. Interestingly, when we blunted antiviral immune responses using clodronate liposomes (which depletes antigen-presenting cells) or cyclosporin (which inhibits cytokine production that regulates T-cell proliferation), significantly lower IFN-γ producing CD8⁺ T cells infiltrated into tendon tissues, resulting in reduced tendon tissues apoptosis and milder disease manifestations. In summary, these data suggest that the degree of ARV virulence and tenosynovitis/arthritis are potentially directly associated with the ability of the virus to traffic massive infiltration of cytotoxic CD8⁺ T cells into the infected tissues. Moreover, the ability to traffic cytotoxic CD8⁺ T cells into infected tendon tissues and the severity of tenosynovitis differ between variants from different ARV genotype cluster groups. However, more than one virus isolate per genotype group needs to be tested to further confirm the association of pathogenicity with genotype. These findings can be used to further examine the interaction of viral and cellular pathways which are essential for the pathogenesis of the disease at the molecular level and to develop effective disease control strategies.

Seroprevalence and Associated Risk Factors of Infectious Bursal Disease in Chickens Managed Under Intensive and Backyard Production Systems in Western Oromia, Ethiopia

Background

Infectious bursal disease (IBD) is a highly contagious viral disease challenging poultry industry throughout the world. It is also among the main obstacles in the different chicken production system in Ethiopia. This study was conducted with the aim of determining seroprevalence and associated risk factors of IBD in backyard and intensively managed chickens of the study area.

Methods

A cross-sectional study was conducted in selected districts of western Oromia on intensive and backyard production systems to investigate seroprevalence of IBD and associated risk factors from September 2020 to August 2021. A total of 384 chickens of either sex, 128 from each district, were included from three randomly selected peasant associations (PAs). In addition, 180 individual poultry keepers, of both sexes, and different educational backgrounds, were included for questionnaire survey (Supplementary Material). Data were analyzed using SPSS Version-20, and results were presented as percentages. The samples were processed by using (ProFLOKIBV, USA) indirect enzyme-linked immunosorbent assay (I-ELISA) kits.

Results

Out of 384 serum samples tested, 66.93% (n = 257) were found positive by indirect ELISA. The highest prevalence was recorded from Sasiga district Balo Bareda PA. Prevalence of IBD showed significant statistical association (p < 0.05) among owner education level, chicken rearing practice, origin and breed. Questionnaire survey results showed the majority of respondents lack sufficient knowledge about IBD and other chicken diseases. The practice of backyard chicken producers on vaccination and treatment of sick birds is limited.

Conclusion

In conclusion, IBD is a major factor hindering production and health of birds. Proper vaccination programs coordinated with awareness creation of chicken owners on how to isolate and treat sick birds should be implemented.

Epidemiology and laboratory diagnosis of very virulent infectious bursal disease virus in vaccinated chickens in Khartoum, Sudan

BACKGROUND

Infectious Bursal Disease (IBD, Gumboro disease) has become more severe than in early outbreaks in the 1980s. The present research aims to study the epidemiology of IBD in Khartoum state and compare some commonly used laboratory techniques for diagnosis.

METHOD

We collected epidemiological data from 30 farms that showed signs suggestive of IBD, estimated the morbidity and mortality rates, and interviewed the owners about the type and the doses of the used vaccines. We collected bursas of Fabricius for virus assays and histopathology. Samples positive in the agar gel immunodiffusion (AGID) test were inoculated onto chicken embryo fibroblast cell culture and embryonated chicken eggs. Twenty-two-day-old chicks were infected experimentally with three selected isolates, and morbidity and mortality rates were compared.

RESULTS

The results showed that 70% of outbreaks occurred between 6 and 8 weeks of age, and the mean mortality rate was 51%. Epidemiologic, clinical, gross, and histopathological findings were characteristic of the severe disease caused by the very virulent IBDvirus (vvIBDV). The farms that used intermediate or the intermediate plus vaccines had lowered mortality compared with the farms that used intermediate vaccines. The AGID was found more sensitive than the counter-immuno-electrophoresis (CIEP) since it detected 83.4% of the IBDV antigen in the samples while the CIEP detected 66.7% of the samples. The reverse transcriptase polymerase chain reaction (RT-PCR) was found to be rapid, specific, and was more sensitive detecting 100% of the tested samples. Virus isolation in embryonated eggs and cell culture was not successful.

CONCLUSION

A vvIBDV is responsible for the recent outbreaks of the disease in Sudan, resulting in a mean high mortality rate of 51%, even in vaccinated flocks. The RT-PCR and AGID are the best methods for laboratory confirmation.

Comparative Immunogenicity Evaluation of Two Infectious Bursal Disease Vaccines Commonly Used in Broiler Chickens in Ethiopia

Purpose

Infectious bursal disease (IBD) is one of the most endemic diseases of commercial poultry in Ethiopia. Vaccination is used as the major means of IBD prevention and control. A study was conducted to compare the immunogenicity of two commercially available IBD vaccines in broiler chicken with maternally derived antibody (MDA).

Methods

A total of 270 day-one-old chicks were randomly assigned to three groups, group 1 vaccinated with product A vaccine at the age of 7 and 19 days and group 2 with product B vaccine on day 15 and 22 while group 3 were kept as control. Six chickens were also randomly selected and bled on day 1 for differential leukocyte count (DLC) and determination of MDA. Representative chickens from each group were bled at 24th and 42nd days of age for antibody titration using the indirect ELISA test. DLC scores were determined in the 1st and 24th days.

Results

The result revealed highly significant differences (P = 0.001) between group 1 and group 2 in DLC at 24th days of age. Antibody titers against IBD were differed significantly (P = 0.02) at 24th and 42nd days of age in broilers vaccinated with product A and product B vaccines.

Conclusion

Both vaccines have induced an adequate immunological response at the end of the experiment; however, product A has shown significantly higher antibody titers against the IBDV and DLC than product B.

Concurrent occurrence of infectious bursal disease and respiratory complex caused by infectious bronchitis and avian influenza (H9N2) in broilers

Infectious bursal disease (IBD) virus is considered one of the commonest immunosuppressive diseases in chickens. The aim of this study was to investigate the concurrent occurrence of subclinical IBD in respiratory complex infections caused by avian influenza (AI, H9N2) virus and infectious bronchitis (IB) virus in broilers. During this study, 800 tissue samples of the trachea, caecal tonsil, spleen, and bursa of Fabricius and 400 blood samples were collected from 20 respiratory complex infected flocks. Detection of pathogens in the tissue samples was performed by RT-PCR for amplification of the VP2 gene of IBD, HA region of AI, and S1 gene of IB viruses. The amplified products were subjected to nucleotide sequence analysis. Blood samples were also tested for the detection of antibodies against IBV by using ELISA and against AIV via using the HI test. Molecular results showed that the tissue samples were positive for field isolates of subclinical IBD (45%), IB (45%), and AI-H9N2 (25%). Co-infections of IBD and IB (30%), IBD and AI (20%), and IBD, IB, and AI (5%) were also detected. Serological results indicated that subclinical IBD infected flocks had lower (P<0.05) antibody titres against IB and AI. In conclusion, prior exposure of broilers to IBD virus increased the incidence of respiratory complex caused by IBV and AIV in broilers, and vaccination against IBD is inevitable to reduce subclinical IBD to minimise the incidence/severity of respiratory complex diseases via improving immune responses to commonly used vaccines in broilers.

Loop-Mediated Isothermal Amplification (LAMP) as a Promising Point-of-Care Diagnostic Strategy in Avian Virus Research

Simple Summary

Many of the existing screening methods of avian viruses depend on clinical symptoms and pathological gross examinations that still necessitate confirmatory microscopic testing. Confirmation of a virus is often conducted at centralized laboratories that are well-equipped with instruments for virus isolation, hemagglutinin inhibition, virus neutralization, ELISA, PCR and qPCR. These assays are known for their great accuracy and sensitivity, and hence are set as standard practices. Nevertheless, limitations arise due to the time, cost and on-site applicability. As the technology progresses, molecular diagnostics should be more accessible to isolated areas and even practicable for use by non-skilled personnel such as farmers and private breeders. One of the point-of-care diagnostic strategies to consider for such matters is loop-mediated isothermal amplification (LAMP).

Abstract

Over the years, development of molecular diagnostics has evolved significantly in the detection of pathogens within humans and their surroundings. Researchers have discovered new species and strains of viruses, while mitigating the viral infections that occur, owing to the accessibility of nucleic acid screening methods such as polymerase chain reaction (PCR), quantitative (real-time) polymerase chain reaction (qPCR) and reverse-transcription qPCR (RT-qPCR). While such molecular detection methods are widely utilized as the benchmark, the invention of isothermal amplifications has also emerged as a reliable tool to improvise on-field diagnosis without dependence on thermocyclers. Among the established isothermal amplification technologies are loop-mediated isothermal amplification (LAMP), recombinant polymerase amplification (RPA), strand displacement activity (SDA), nucleic acid sequence-based amplification (NASBA), helicase-dependent amplification (HDA) and rolling circle amplification (RCA). This review highlights the past research on and future prospects of LAMP, its principles and applications as a promising point-of-care diagnostic method against avian viruses.

Infectious bursal disease virus in free-living wild birds: A systematic review and meta-analysis of its sero-viroprevalence on a global scale

Infectious bursal disease virus (IBDV) is an economically important pathogen for poultry, whereas knowledge of its occurrence in non-poultry hosts is limited. The objective of this systematic review and meta-analysis is to summarize the up-to-date knowledge about the sero-viroprevalence of IBDV in wild birds on a global scale. A computerized literature research was performed on PubMed, Scopus, CAB Direct and Web of Science to find relevant publications, along with the screening of reference lists. Journal articles, book chapters, scientific correspondences, conference proceedings and short communications on IBDV virological and/or serological surveys in free-living wild birds published between 1970 and 2021 were considered as eligible. Among 184 studies found, 36 original contributions met the pre-established criteria. A random-effect model was applied to calculate pooled seroprevalence estimates with 95% confidence intervals, whereas the paucity of virological studies (n = 6) only allowed a qualitative description of the data. The pooled seroprevalence was estimated to be 6% (95% CI: 3%-9%) and a high heterogeneity was detected (I²  = 96%). Sub-group analyses were not performed due to the scarcity of available information about hypothetical moderators. With respect to virological studies, IBDV was detected in Anseriformes, Columbiformes, Galliformes, Passeriformes and Pelecaniformes and different strains related to poultry infection were isolated. Our estimates of serological data showed a moderate exposure of wild birds to IBDV. The susceptibility of different species to IBDV infection underlines their potential role in its epidemiology at least as carriers or spreaders. Indeed, the isolation of IBDV in healthy wild birds with a migratory attitude might contribute to a long-distance spread of the virus and to strain diversity. While a wild reservoir host could not be clearly identified, we believe our work provides useful insights for conducting future surveys which are needed to broaden our knowledge of IBDV occurrence in wild birds.

Development of a Novel Assay Based on Plant-Produced Infectious Bursal Disease Virus VP3 for the Differentiation of Infected From Vaccinated Animals

Infectious bursal disease virus is the causative agent of Gumboro disease, a severe infection that affects young chickens and is associated with lymphoid depletion in the bursa of Fabricius. Traditional containment strategies are based either on inactivated or live-attenuated vaccines. These approaches have several limitations such as residual virulence or low efficacy in the presence of maternally derived antibodies (MDA) but, most importantly, the impossibility to detect the occurrence of natural infections in vaccinated flocks. Therefore, the development of novel vaccination strategies allowing the differentiation of infected from vaccinated animals (DIVA) is a priority. Recently, commercial vectored and experimental subunit vaccines based on VP2 have been proved effective in protecting from clinical disease and posed the basis for the development of novel DIVA strategies. In this study, an engineered version of the VP3 protein of IBDV (His-VP3) was produced in plants, successfully purified from Nicotiana benthamiana leaves, and used to develop an enzyme-linked immunosorbent assay (ELISA) for the detection of anti-VP3 antibodies. The His-VP3 ELISA was validated with a panel of 180 reference sera and demonstrated to have 100% sensitivity (95% CI: 94.7-100.0) and 94.17% specificity (95% CI: 88.4-97.6). To evaluate the application of His-VP3 ELISA as a DIVA test, the novel assay was used to monitor, in combination with a commercial kit, detecting anti-VP2 antibodies, the immune response of chickens previously immunized with an inactivated IBDV vaccine, a recombinant Turkey herpes virus carrying the VP2 of IBDV (HVT-ND-IBD) or with plant-produced VP2 particles. The combined tests correctly identified the immune status of the vaccinated specific pathogen free white-leghorn chickens. Moreover, the His-VP3 ELISA correctly detected MDA against VP3 in commercial broiler chicks and showed that antibody titers fade with time, consistent with the natural decrease of maternally derived immunity. Finally, the novel assay, in combination with a VP2-specific ELISA, demonstrated its potential application as a DIVA test in chickens inoculated with VP2-based vaccines, being able to detect the seroconversion after challenge with a very virulent IBDV strain.

Genome-Wide Analysis of Alternative Splicing during Host-Virus Interactions in Chicken

The chicken is a model animal for the study of evolution, immunity and development. In addition to their use as a model organism, chickens also represent an important agricultural product. Pathogen invasion has already been shown to modulate the expression of hundreds of genes, but the role of alternative splicing in avian virus infection remains unclear. We used RNA-seq data to analyze virus-induced changes in the alternative splicing of Gallus gallus, and found that a large number of alternative splicing events were induced by virus infection both in vivo and in vitro. Virus-responsive alternative splicing events preferentially occurred in genes involved in metabolism and transport. Many of the alternatively spliced transcripts were also expressed from genes with a function relating to splicing or immune response, suggesting a potential impact of virus infection on pre-mRNA splicing and immune gene regulation. Moreover, exon skipping was the most frequent AS event in chickens during virus infection. This is the first report describing a genome-wide analysis of alternative splicing in chicken and contributes to the genomic resources available for studying host-virus interaction in this species. Our analysis fills an important knowledge gap in understanding the extent of genome-wide alternative splicing dynamics occurring during avian virus infection and provides the impetus for the further exploration of AS in chicken defense signaling and homeostasis.

Oral Immunization With Plant-Based Vaccine Induces a Protective Response Against Infectious Bursal Disease

Infectious bursal disease virus (IBDV) is the etiological agent of an immunosuppressive and highly contagious disease that affects young birds causing important economic losses in the poultry industry worldwide. We have previously developed a plant-based vaccine candidate for infectious bursal disease (IBD) that is able to protect against infection with IBDV when administered through intramuscular (im) route. Given that oral vaccination is non-invasive and stimulates the immunity of the mucosal gastrointestinal surface, the initial site of contact and entry of IBDV, the aim of this work was to study if our immunogen was also able to elicit a protective immune response when orally administered. We demonstrated that 85% of the animals that received two oral doses of the vaccine formulation and all animals that were orally boosted after an im prime scheme developed virus neutralizing antibodies and were protected against IBDV infection, evidenced by the bursa/body weight (BB) ratio, absence of T-cell infiltration, and low viral load in bursa. Although mild to moderate bursal damage was observed in some of these animals, these lesions were not as severe as the ones observed in challenged control groups, which also presented signs of acute inflammation, bursal atrophy, T-cell infiltration, and absence of viral clearance. These results show that two immunizations with our recombinant immunogen are able to induce a specific and protective immune response in chicken against IBDV when orally administered in a prime/boost scheme or when the oral boost follows an im prime scheme. In conclusion, our oral plant-based vaccine candidate could represent a viable alternative to conventional vaccines and is of great interest to the poultry industry.

Hemorrhagic Hepatopathy in Broiler Breeder Pullets: Gross and Microscopic Pathology and Factors Associated with Incidence

Hemorrhagic hepatopathy is a syndrome reported in layer pullets resulting in mortality and lesions including hepatic, splenic, and intestinal necrosis; hepatic and splenic enlargement; hemorrhages; amyloidosis of the muscle, spleen, and liver; accumulation of noncoagulated hemorrhagic fluid in the coelom; and frequently, granulomatous myositis at bacterin injection sites. The syndrome is characterized in the literature in table egg layer pullets and is thought to be associated with the administration of bacterin vaccines, namely, frequently Salmonella enterica subsp. enterica bacterins. Hemorrhagic hepatopathy is recognized by industry veterinarians as also occurring infrequently in broiler breeder pullets in the United States. As the condition is likely due to an inflammatory process in response to bacterial lipopolysaccharide inoculation, it is important to characterize both the pathologic changes and predisposing factors for the condition in broiler breeds, which are immunologically different from table egg layer breeds. In this study, we characterize the gross and microscopic lesions observed in a series of diagnostic laboratory cases of hemorrhagic hepatopathy in broiler breeder pullets and suggest a possible pathophysiology for the condition. Additionally, we report results from a case survey of the United States broiler industry that suggest that the condition is due to a reaction to bacterin vaccination and that certain bacterin products may predispose pullet flocks to develop the condition. Although further research is indicated, these findings establish hemorrhagic hepatopathy as a pathologic condition of broiler breeder pullets and may aid in the diagnosis and prevention of the syndrome.

Folic acid enhances proinflammatory and antiviral molecular pathways in chicken B-lymphocytes infected with a mild infectious bursal disease virus

1. This study evaluated the effect of folic acid (FA) supplementation on the proinflammatory and antiviral molecular pathways of B-lymphocytes infected with a modified live IBDV (ST-12) mild vaccine strain during a timed post-infection analysis.2. A chicken B-lymphocytes (DT-40) cell line was cultured in triplicate at a concentration of 5 × 10⁵ cells per well in 24-well plates; and was divided into three groups: 1: No virus, FA; 2: Virus, no FA; 3: Virus + FA at a concentration of 3.96 mM. The experiment was repeated three times.3. Cells in groups 2 and 3 were infected with a modified live IBDV (ST-12) mild vaccine strain at one multiplicity of infection (MOI: 1). After 1 hour of virus adsorption, samples were collected at 0, 3, 6, 12, 24 and 36 hours post-infection (hpi).4. The modified live IBDV (ST-12) mild vaccine strain triggered a B-lymphocyte specific immune response associated with the upregulation of genes involved in virus recognition (Igß), virus sensing (TLR-2, TLR-3, TLR-4 and MDA5), signal transduction and regulation (TRIF, MyD88 and IRF7), and the antiviral effector molecules (IFN-α, OAS, PKR, and viperin).5. FA supplementation modulated IBDV replication and regulated the proinflammatory and antiviral downstream molecular pathways.6. In conclusion, the low virulent pathotype serotype I modified live IBDV (ST-12) mild vaccine strain was able to trigger and mount an immune response in chicken B-lymphocytes without affecting B-cell viability. FA supplementation modulated B lymphocytes response and improved their innate immune proinflammatory and antiviral response molecular pathways.

Targeting Haemagglutinin Antigen of Avian Influenza Virus to Chicken Immune Cell Receptors Dec205 and CD11c Induces Differential Immune-Potentiating Responses

Improving the immunogenicity and protective efficacy of vaccines is critical to reducing disease impacts. One strategy used to enhance the immunogenicity of vaccines is the selective delivery of protective antigens to the antigen presenting cells (APCs). In this study, we have developed a targeted antigen delivery vaccine (TADV) system by recombinantly fusing the ectodomain of hemagglutinin (HA) antigen of H9N2 influenza A virus to single chain fragment variable (scFv) antibodies specific for the receptors expressed on chicken APCs; Dec205 and CD11c. Vaccination of chickens with TADV containing recombinant H9HA Foldon-Dec205 scFv or H9HA Foldon-CD11c scFv proteins elicited faster (as early as day 6 post primary vaccination) and higher anti-H9HA IgM and IgY, haemagglutination inhibition, and virus neutralisation antibodies compared to the untargeted H9HA protein. Comparatively, CD11c scFv conjugated H9HA protein showed higher immunogenic potency compared to Dec205 scFv conjugated H9HA protein. The higher immune potentiating ability of CD11c scFv was also reflected in ex-vivo chicken splenocyte stimulation assay, whereby H9HA Foldon-CD11c scFv induced higher levels of cytokines (IFNγ, IL6, IL1β, and IL4) compared to H9HA Foldon-Dec205 scFv. Overall, the results conclude that TADV could be a better alternative to the currently available inactivated virus vaccines.

Chicken Mesenchymal Stem Cells and Their Applications: A Mini Review

Simple Summary

Mesenchymal stem cells (MSCs) are multipotent stem cells that are capable of differentiation into bone, muscle, fat, and closely related lineages and express unique and specific cell surface markers. They can be used as an avian culture model to better understand osteogenic, adipogenic, and myogenic pathways. Moreover, MSCs could also be used as a model to study various developmental and physiological processes in avian and other species. To obtain a comprehensive overview of this topic, the keywords “mesenchymal stem cells”, “chicken”, “disease”, “chicken dermatitis”, “viral infections in chicken”, and “antibiotics in chicken” were searched in WOS and PUBMED databases to obtain relevant information.

Abstract

Mesenchymal stem cells (MSCs) are multipotent progenitor cells that adhere to plastic; express the specific markers CD29, CD44, CD73, CD90, and CD105; and produce cytokines and growth factors supporting and regulating hematopoiesis. MSCs have capacity for differentiating into osteocytes, chondrocytes, adipocytes, and myocytes. They are useful for research toward better understanding the pathogenic potential of the infectious bursal disease virus, mineralization during osteogenesis, and interactions between MSCs as a feeder layer to other cells. MSCs are also important for immunomodulatory cell therapy, can provide a suitable strategy model for coculture with pathogens causing dermatitis disorders in chickens, can be cultured in vitro with probiotics and prebiotics with a view to eliminate the feeding of antibiotic growth promoters, and offer cell-based meat production. Moreover, bone marrow-derived MSCs (BM-MSCs) in coculture with hematopoietic progenitor/stem cells (HPCs/HSCs) can support expansion and regulation of the hematopoiesis process using the 3D-culture system in future research in chickens. MSCs’ several advantages, including ready availability, strong proliferation, and immune modulatory properties make them a suitable model in the field of stem cell research. This review summarizes current knowledge about the general characterization of MSCs and their application in chicken as a model organism.

Functional prediction of de novo uni-genes from chicken transcriptomic data following infectious bursal disease virus at 3-days post-infection

BACKGROUND

Infectious bursal disease (IBD) is an economically very important issue to the poultry industry and it is one of the major threats to the nation's food security. The pathogen, a highly pathogenic strain of a very virulent IBD virus causes high mortality and immunosuppression in chickens. The importance of understanding the underlying genes that could combat this disease is now of global interest in order to control future outbreaks. We had looked at identified novel genes that could elucidate the pathogenicity of the virus following infection and at possible disease resistance genes present in chickens.

RESULTS

A set of sequences retrieved from IBD virus-infected chickens that did not map to the chicken reference genome were de novo assembled, clustered and analysed. From six inbred chicken lines, we managed to assemble 10,828 uni-transcripts and screened 618 uni-transcripts which were the most significant sequences to known genes, as determined by BLASTX searches. Based on the differentially expressed genes (DEGs) analysis, 12 commonly upregulated and 18 downregulated uni-genes present in all six inbred lines were identified with false discovery rate of q-value < 0.05. Yet, only 9 upregulated and 13 downregulated uni-genes had BLAST hits against the Non-redundant and Swiss-Prot databases. The genome ontology enrichment keywords of these DEGs were associated with immune response, cell signalling and apoptosis. Consequently, the Weighted Gene Correlation Network Analysis R tool was used to predict the functional annotation of the remaining unknown uni-genes with no significant BLAST hits. Interestingly, the functions of the three upregulated uni-genes were predicted to be related to innate immune response, while the five downregulated uni-genes were predicted to be related to cell surface functions. These results further elucidated and supported the current molecular knowledge regarding the pathophysiology of chicken's bursal infected with IBDV.

CONCLUSION

Our data revealed the commonly up- and downregulated novel uni-genes identified to be immune- and extracellular binding-related, respectively. Besides, these novel findings are valuable contributions in improving the current existing integrative chicken transcriptomics annotation and may pave a path towards the control of viral particles especially towards the suppression of IBD and other infectious diseases in chickens.

Genome Evolution of Two Genetically Homogeneous Infectious Bursal Disease Virus Strains During Passages in vitro and ex vivo in the Presence of a Mutagenic Nucleoside Analog

The avibirnavirus infectious bursal disease virus (IBDV) is responsible for a highly contagious and sometimes lethal disease of chickens (Gallus gallus). IBDV genetic variation is well-described for both field and live-attenuated vaccine strains, however, the dynamics and selection pressures behind this genetic evolution remain poorly documented. Here, genetically homogeneous virus stocks were generated using reverse genetics for a very virulent strain, rvv, and a vaccine-related strain, rCu-1. These viruses were serially passaged at controlled multiplicities of infection in several biological systems, including primary chickens B cells, the main cell type targeted by IBDV in vivo. Passages were also performed in the absence or presence of a strong selective pressure using the antiviral nucleoside analog 7-deaza-2'-C-methyladenosine (7DMA). Next Generation Sequencing (NGS) of viral genomes after the last passage in each biological system revealed that (i) a higher viral diversity was generated in segment A than in segment B, regardless 7DMA treatment and viral strain, (ii) diversity in segment B was increased by 7DMA treatment in both viruses, (iii) passaging of IBDV in primary chicken B cells, regardless of 7DMA treatment, did not select cell-culture adapted variants of rvv, preserving its capsid protein (VP2) properties, (iv) mutations in coding and non-coding regions of rCu-1 segment A could potentially associate to higher viral fitness, and (v) a specific selection, upon 7DMA addition, of a Thr329Ala substitution occurred in the viral polymerase VP1. The latter change, together with Ala270Thr change in VP2, proved to be associated with viral attenuation in vivo. These results identify genome sequences that are important for IBDV evolution in response to selection pressures. Such information will help tailor better strategies for controlling IBDV infection in chickens.

Novel Vaccine Technologies in Veterinary Medicine: A Herald to Human Medicine Vaccines

The success of inactivated and live-attenuated vaccines has enhanced livestock productivity, promoted food security, and attenuated the morbidity and mortality of several human, animal, and zoonotic diseases. However, these traditional vaccine technologies are not without fault. The efficacy of inactivated vaccines can be suboptimal with particular pathogens and safety concerns arise with live-attenuated vaccines. Additionally, the rate of emerging infectious diseases continues to increase and with that the need to quickly deploy new vaccines. Unfortunately, first generation vaccines are not conducive to such urgencies. Within the last three decades, veterinary medicine has spearheaded the advancement in novel vaccine development to circumvent several of the flaws associated with classical vaccines. These third generation vaccines, including DNA, RNA and recombinant viral-vector vaccines, induce both humoral and cellular immune response, are economically manufactured, safe to use, and can be utilized to differentiate infected from vaccinated animals. The present article offers a review of commercially available novel vaccine technologies currently utilized in companion animal, food animal, and wildlife disease control.

The Novel Genetic Background of Infectious Bursal Disease Virus Strains Emerging from the Action of Positive Selection

The circulation in Europe of novel reassortant strains of infectious bursal disease virus (IBDV), containing a unique genetic background composition, represents a serious problem for animal health. Since the emergence of this novel IBDV mosaic was first described in Poland, this scenario has become particularly attractive to uncover the evolutionary forces driving the genetic diversity of IBDV populations. This study additionally addressed the phenotypic characterization of these emergent strains, as well as the main features affecting the viral fitness during the competition process of IBDV lineages in the field. Our results showed how different evolutionary mechanisms modulate the genetic diversity of co-existent IBDV lineages, leading to the error catastrophe effect, Muller ratchet effect, or prevalence, depending on their genetic compositions. We also determined that the action of the positive selection pressure, depending on the genomic segment on which it is acting, can drive two main phenotypes for IBDV: immune-escaping strains from the selection on segment A or strains with functional advantages from the selection on segment B. This last group seems to possess an increased fitness landscape in the viral quasispecies composition, presenting better adaptability to dissimilar environmental conditions and likely becoming the dominant population. The reassortant strains also exhibited a lower mortality rate compared with the well-known vvIBDV strains, which can facilitate their spreading.

The expression in plants of an engineered VP2 protein of Infectious Bursal Disease Virus induces formation of structurally heterogeneous particles that protect from a very virulent viral strain

Infectious Bursal Disease Virus (IBDV), the etiological agent of Gumboro disease, causes mortality and immunosuppression in chickens and major losses to poultry industry worldwide. The IBDV major capsid protein VP2 is considered the best candidate for the production of novel subunit vaccines. This structural protein contains the major conformational epitopes responsible for the induction of IBDV neutralizing antibodies in chickens and has been demonstrated able to form supramolecular structures in yeast and insect cells. The aim of this study was to express an engineered version of the VP2 protein (His-pVP2) to verify its ability to self-assemble into virus-like particles in plants. The recombinant VP2 was transiently expressed by agroinfiltration in Nicotiana benthamiana and transmission electron microscopy of sucrose density gradient fractions revealed the presence of a mixed population of differently shaped particles ranging from spherical capsids, with a diameter between ~25 and ~70 nm, to tubular structures, with variable length (from 100 to 400 nm). The recombinant VP2-based particles when used for the intramuscular immunization of specific-pathogen-free chicks resulted able to induce the production of anti-IBDV specific antibodies at titers comparable to those induced by a commercial vaccine. Moreover, all the immunized birds survived to the challenge with a Moroccan very virulent IBDV strain with no major histomorphological alterations of the Bursa of Fabricius, similarly to what obtained with the commercial inactivated vaccine.

Development of lateral flow assay based on anti-IBDV IgY for the rapid detection of Gumboro disease in poultry

The poultry industry faces serious problems against infectious diseases, including Gumboro, which is caused by contagious bursal disease virus (IBDV). IBDV infects the bursa of Fabricius (BF), a lymphoid organ for controlling the B-cell maturation. Thus, it can trigger the secondary infection's vulnerability, leading to the high mortality and morbidity of the chicken. Moreover, managing the Gumboro post-outbreaks also requires considerable time and costs. Besides vaccination programs, the early detection of IBDV is vital as an outbreak control strategy. The most popular diagnostic tool is a lateral flow immunoassay or a rapid test that meets ASSURED (Affordable, Sensitive, Specific, User-friendly, Rapid and Robust, Equipment-free, and Deliverable to end-users) criteria. In this study, the lateral flow immunoassay was successfully developed based on anti-IBDV IgY as the bio receptor. Anti-IBDV IgY was successfully isolated from Isa Brown's egg yolk. The detection system showed an acceptable affinity against the inactivated IBDV sample (1.5 × 10³ TCID₅₀). In addition, it did not react with avian influenza and Newcastle disease viruses, demonstrating a good specificity of the test.

Development of a Viral-Like Particle Candidate Vaccine Against Novel Variant Infectious Bursal Disease Virus

Infectious bursal disease (IBD), an immunosuppressive disease of young chickens, is caused by infectious bursal disease virus (IBDV). Novel variant IBDV (nVarIBDV), a virus that can evade immune protection against very virulent IBDV (vvIBDV), is becoming a threat to the poultry industry. Therefore, nVarIBDV-specific vaccine is much needed for nVarIBDV control. In this study, the VP2 protein of SHG19 (a representative strain of nVarIBDV) was successfully expressed using an Escherichia coli expression system and further purified via ammonium sulfate precipitation and size-exclusion chromatography. The purified protein SHG19-VP2-466 could self-assemble into 25-nm virus-like particle (VLP). Subsequently, the immunogenicity and protective effect of the SHG19-VLP vaccine were evaluated using animal experiments, which indicated that the SHG19-VLP vaccine elicited neutralization antibodies and provided 100% protection against the nVarIBDV. Furthermore, the protective efficacy of the SHG19-VLP vaccine against the vvIBDV was evaluated. Although the SHG19-VLP vaccine induced a comparatively lower vvIBDV-specific neutralization antibody titer, it provided good protection against the lethal vvIBDV. In summary, the SHG19-VLP candidate vaccine could provide complete immune protection against the homologous nVarIBDV as well as the heterologous vvIBDV. This study is of significance to the comprehensive prevention and control of the recent atypical IBD epidemic.

Novel variant infectious bursal disease virus suppresses Newcastle disease vaccination in broiler and layer chickens

Newcastle disease (ND) is one of the most important avian diseases that seriously threaten the poultry industry worldwide. Sometimes vaccination might not effectively reduce ND occurrence in some poultry farms for unclear reasons. Infectious bursal disease (IBD) is one of the most important immunosuppressive diseases, and the novel variant IBD virus (IBDV) is threatening chicken farms in China. This study evaluated the influence of the novel variant IBDV (SHG19 strain) on immunization of ND vaccine (LaSota strain) in broiler and layer chickens. In commercial broilers, the hemagglutination inhibition antibody titers against LaSota strain were decreased by the prior infection of the novel variant IBDV. Pathological examination revealed that the novel variant IBDV severely damaged the key immune organs of the bursa and spleen, and the B lymphocytes in the bursa were severely destroyed, which was the primary reason involved in the immunosuppression on ND vaccination. Moreover, the novel variant IBDV dramatically reduced the BW of infected broilers by about 16% compared to that of control, which indicated huge economic losses. Furthermore, this study confirmed the immunosuppression induced by the novel variant IBDV in specific pathogen–free layer chickens. In this study, it was discovered that the novel variant IBDV could interfere with ND vaccination in both broilers and layers, which was one important factor involved in immune failure in poultry farms. This study therefore suggests the urgency to control the novel variant IBDV infection for healthy breeding.

Ex vivo rescue of recombinant very virulent IBDV using a RNA polymerase II driven system and primary chicken bursal cells

Infectious Bursal Disease Virus (IBDV), a member of the Birnaviridae family, causes an immunosuppressive disease in young chickens. Although several reverse genetics systems are available for IBDV, the isolation of most field-derived strains, such as very virulent IBDV (vvIBDV) and their subsequent rescue, has remained challenging due to the lack of replication of those viruses in vitro. Such rescue required either the inoculation of animals, embryonated eggs, or the introduction of mutations in the capsid protein (VP2) hypervariable region (HVR) to adapt the virus to cell culture, the latter option concomitantly altering its virulence in vivo. We describe an improved ex vivo IBDV rescue system based on the transfection of an avian cell line with RNA polymerase II-based expression vectors, combined with replication on primary chicken bursal cells, the main cell type targeted in vivo of IBDV. We validated this system by rescuing to high titers two recombinant IBDV strains: a cell-culture adapted attenuated strain and a vvIBDV. Sequencing of VP2 HVR confirmed the absence of unwanted mutations that may alter the biological properties of the recombinant viruses. Therefore, this approach is efficient, economical, time-saving, reduces animal suffering and can be used to rescue other non-cell culture adapted IBDV strains.

Sequence-based comparison of field and vaccine strains of infectious bursal disease virus in Ethiopia reveals an amino acid mismatch in the immunodominant VP2 protein

Sequencing of the VP2 region was carried out to identify amino acid mismatches between vaccine strains and field isolates of infectious bursal disease virus (IBDV). Viruses were isolated in chicken embryo fibroblast (DF-1) cells using pooled samples of bursa collected from nine outbreaks, which affected 30,250 chickens in five localities, with an overall mortality of 47.87%. Virus strains were identified by comparing the deduced amino acid sequence between positions 232 and 446 of the immunodominant VP2 epitope. All of the pooled samples were positive for IBDV. RT-PCR yielded a 645-bp DNA fragment of the VP2 gene. Phylogenetic analysis of this fragment revealed clustering of these isolates with very virulent IBDV strains. The amino acid sequences of these isolates were identical to those of the European very virulent strains UK 661 and DV 86, except at position 222, but differed from the vaccine strains used in Ethiopia, suggesting the possible introduction of virulent virus strains to Ethiopia from Europe. Our study demonstrates the widespread presence of very virulent strains of IBDV on poultry farms in Ethiopia and demonstrates the need to evaluate the protective level of existing vaccines against circulating field viruses.