A proposed nomenclature for infectious bursal disease virus isolates

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.

Exploring Variability: Inflammation Mediator Levels across Tissues and Time in Poultry Experimentally Infected by the G1a and G6 Genogroups of Infectious Bursal Disease Virus (IBDV)

Infectious bursal disease virus (IBDV) is a significant burden for poultry production and market due to both direct disease and induced immunosuppression. In the present study, the expression of different cytokines in the bursa of Fabricius and thymus was evaluated during a 28-day-long experimental infection with two strains classified in the G1a (Classical) and G6 (ITA) genogroups. Although both strains significantly affected and modulated the expression of different molecules, the G6 strain seemed to induce a delayed immune response or suppress it more promptly. A recovery in the expression of several mediators was observed in the G1a-infected group at the end of the study, but not in the G6 one, further supporting a more persistent immunosuppression. This evidence fits with the higher replication level previously reported for the G6 and with the clinical outcome, as this genotype, although subclinical, has often been considered more immunosuppressive. However, unlike other studies focused on shorter time periods after infection, the patterns observed in this paper were highly variable and complex, depending on the strain, tissue, and time point, and characterized by a non-negligible within-group variability. Besides confirming the strain/genogroup effect on immune system modulation, the present study suggests the usefulness of longer monitoring activities after experimental infection to better understand the complex patterns and interactions with the host response.

The booster immunization using commercial vaccines effectively protect chickens against novel variants of infectious bursal disease virus (genotype A2dB1)

The novel variant IBDV (nVarIBDV, genotype A2dB1), characterized by bursal atrophy of fabricius and decreased lymphocytes, has been emerging on a large scale in Asia (including China) since late 2018. nVarIBDV is a new threat to the poultry industry, yet the currently licensed commercial vaccines, including the live viral vector vaccine, IBDV immune complex vaccine or VP2 subunit vaccine, are ineffective against nVarIBDV infection. In this study, specific-pathogen-free (SPF) chickens and broilers divided into 3 groups were vaccinated with the live viral vector vaccine, the VP2 subunit vaccine or the IBDV immune complex vaccine at 1 day-old, respectively. The SPF chickens received a secondary vaccination with the live B87 strain vaccine at 11-day-old. The bursa/body weight ratio, histopathology lesion of the bursa, and the differentiation between infected and vaccinated animals (DIVA) by qRT-PCR confirmed that the live viral vector vaccine or immune complex vaccine plus live B87 strain booster could provide at least 80% protection against the FJ2019-01 strain of nVarIBDV in SPF chickens. The broilers also received a secondary vaccination using a live W2512 G-61 strain vaccine at 14-day-old, and analyses showed that the VP2 subunit vaccine or immune complex vaccine plus the live W2512 G-61 strain booster also provided more than 80% protection against the FJ2019-01 strain of nVarIBDV. Unfortunately, the live viral vector vaccine plus live W2512 G-61 strain booster provided poor to moderate protection against FJ2019-01 in broilers. These findings suggest that combining commercial vaccines with rational booster immunization can effectively protect chickens against an nVarIBDV challenge.

Isolation, Molecular, and Histopathological Patterns of a Novel Variant of Infectious Bursal Disease Virus in Chicken Flocks in Egypt

After an extended period of detecting classical virulent, attenuated, and very virulent IBDV, a novel variant (nVarIBDV) was confirmed in Egypt in this study in 18, IBD vaccinated, chicken flocks aged 19-49 days. Partial sequence of viral protein 2 (VP2) [219 aa, 147-366, resembling 657 bp] of two obtained isolates (nos. 3 and 4) revealed nVarIBDV (genotype A2d) and OR682618 and OR682619 GenBank accession numbers were obtained. Phylogenetic analysis revealed that both nVarIBDV isolates were closely related to nVarIBDV strains (A2d) circulating in China, exhibiting 100% identity to SD-2020 and 99.5-98.1% similarity to ZD-2018-1, QZ, GX and SG19 strains, respectively. Similarity to USA variant strains, belonging to genotypes A2b (9109), A2c (GLS) and A2a (variant E), respectively, was 95.5-92.6%. Also, the VP2 hypervariable region in those two, A2d, isolates revealed greater similarities to Faragher 52/70 (Vaxxitek®) at 90.4% and to an Indian strain (Ventri-Plus®) and V217 (Xtreme®) at 89.7% and 86-88.9% in other vaccines. Histopathological examination of both the bursa of Fabricius and spleen collected from diseased chickens in flock no. 18 revealed severe atrophy. In conclusion, further studies are required to investigate the epidemiological situation of this novel genotype across the country, and to assess various vaccine protections against nVarIBDV. Additionally, vaccination of breeders with inactivated IBD vaccines including this nVarIBDV is essential to obtain specific maternal antibodies in their broilers.

Pros and Cons on Use of Live Viral Vaccines in Commercial Chicken Flocks

The poultry industry is the largest source of meat and eggs for the growing human population worldwide. Key concerns in poultry farming are nutrition, management, flock health, and biosecurity measures. As part of the flock health, use of live viral vaccines plays a vital role in the prevention of economically important and common viral diseases. This includes diseases and production losses caused by Newcastle disease virus, infectious bronchitis virus, infectious laryngotracheitis virus, infectious bursal disease virus, Marek's disease virus, chicken infectious anemia virus, avian encephalomyelitis virus, fowlpox virus, and avian metapneumovirus. These viruses cause direct and indirect harms, such as financial losses worth millions of dollars, loss of protein sources, and threats to animal welfare. Flock losses vary by type of poultry, age of affected animals, co-infections, immune status, and environmental factors. Losses in broiler birds can consist of high mortality, poor body weight gain, high feed conversion ratio, and increased carcass condemnation. In commercial layers and breeder flocks, losses include higher than normal mortality rate, poor flock uniformity, drops in egg production and quality, poor hatchability, and poor day-old-chick quality. Despite the emergence of technology-based vaccines, such as inactivated, subunit, vector-based, DNA or RNA, and others, the attenuated live vaccines remain as important as before. Live vaccines are preferred in the global veterinary vaccine market, accounting for 24.3% of the global market share in 2022. The remaining 75% includes inactivated, DNA, subunit, conjugate, recombinant, and toxoid vaccines. The main reason for this is that live vaccines can induce innate, mucosal, cellular, and humoral immunities by single or multiple applications. Some live vaccine combinations provide higher and broader protection against several diseases or strains of viruses. This review aimed to explore insights on the pros and cons of attenuated live vaccines commonly used against major viral infections of the global chicken industry, and the future road map for improvement.

The attenuated live vaccine strain W2512 provides protection against novel variant infectious bursal disease virus

Infectious bursal disease virus (IBDV) causes an acute and highly contagious infectious disease characterized by severe immunosuppression, causing great economic losses to the poultry industry globally. Over the past 30 years, this disease has been well controlled through vaccination and strict biosafety measures. However, novel variant IBDV strains have emerged in recent years, posing a new threat to the poultry industry. Our previous epidemiological survey showed that few novel variant IBDV strains had been isolated from chickens immunized with the attenuated live vaccine W2512-, suggesting that this vaccine is efficacious against novel variant strains. Here, we report the protective effect of the W2512 vaccine against novel variant strains in SPF chickens and commercial yellow-feathered broilers. We found that W2512 causes severe atrophy of the bursa of Fabricius in SPF chickens and commercial yellow-feathered broilers, induces high levels of antibodies against IBDV, and protects chickens from infection with the novel variant strains via a placeholder effect. This study highlights the protective effect of commercial attenuated live vaccines against the novel IBDV variant and provides guidance for the prevention and control of this disease.

Phylogenotyping of infectious bursal disease virus in Vietnam according to the newly unified genotypic classification scheme

Since 1987, infectious bursal disease virus (IBDV) has circulated and evolved in Vietnam, but little is known about the genotypes present. IBDV samples were collected in 1987, 2001-2006, 2008, 2011, 2015-2019, and 2021 in 18 provinces. We conducted phylogenotyping analysis based on an alignment of 143 VP2-HVR (hypervariable region) sequences from 64 Vietnamese isolates (26 previous and 38 additional sequences and two vaccines, and alignment of 82 VP1 B-marker sequences, including one vaccine and four Vietnamese field strains. The analysis identified three A-genotypes, A1, A3, and A7, and two B-genotypes, B1 and B3, among the Vietnamese IBDV isolates. The lowest average evolutionary distance (8.6%) was seen between the A1 and A3 genotypes, and the highest (21.7%) was between A5 and A7, while there was a distance of 14% between B1 and B3 and 17% between B3 and B2. Unique signature residues were observed for genotypes A2, A3, A5, A6, and A8, which could be used for genotypic discrimination. A timeline statistical summary revealed that the A3-genotype predominated (79.8% presence) in Vietnam from 1987 to 2021 and that it remained the dominant IBDV genotype over the last five years (2016-2021). The current study contributes to a better understanding of the circulating genotypes and evolution of IBDV in Vietnam and worldwide.

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.

PRMT5 Facilitates Infectious Bursal Disease Virus Replication through Arginine Methylation of VP1

The infectious bursal diseases virus (IBDV) polymerase, VP1 protein, is responsible for transcription, initial translation and viral genomic replication. Knowledge about the new kind of post-translational modification of VP1 supports identification of novel drugs against the virus. Because the arginine residue is known to be methylated by protein arginine methyltransferase (PRMT) enzyme, we investigated whether IBDV VP1 is a substrate for known PRMTs. In this study, we show that VP1 is specifically associated with and methylated by PRMT5 at the arginine 426 (R426) residue. IBDV infection causes the accumulation of PRMT5 in the cytoplasm, which colocalizes with VP1 as a punctate structure. In addition, ectopic expression of PRMT5 significantly enhances the viral replication. In the presence of PMRT5, enzyme inhibitor and knockout of PRMT5 remarkably decreased viral replication. The polymerase activity of VP1 was severely damaged when R426 mutated to alanine, resulting in impaired viral replication. Our study reports a novel form of post-translational modification of VP1, which supports its polymerase function to facilitate the viral replication. IMPORTANCE Post-translational modification of infectious bursal disease virus (IBDV) VP1 is important for the regulation of its polymerase activity. Investigation of the significance of specific modification of VP1 can lead to better understanding of viral replication and can probably also help in identifying novel targets for antiviral compounds. Our work demonstrates the molecular mechanism of VP1 methylation mediated by PRMT5, which is critical for viral polymerase activity, as well as viral replication. Our study expands a novel insight into the function of arginine methylation of VP1, which might be useful for limiting the replication of IBDV.

Infectious bursal disease virus in Western Europe: the rise of reassortant strains as the dominant field threat

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

Comparative Safety, Immunogenicity, and Efficacy of CEF Cell-Based and DF-1 Cell Line Adapted Infectious Bursal Disease Vaccines in Specific-Pathogen-Free Chickens

Infectious bursal disease (IBD) is an immunosuppressive and economically important disease of young chickens caused by infectious bursal disease virus (IBDV). The National Veterinary Institute (Bishoftu, Ethiopia) produces intermediate IBDV vaccine using primary chicken embryo fibroblast (CEF) cells, a method with technical and economical cumbersome. This study assessed the safety, immunogenicity, and efficacy of DF-1 cell line-adapted IBDV LC–75 vaccine strain in reference to the CEF-based vaccine. Confluent monolayer of DF-1 cells was infected with IBDV and cells with cytopathic effects were passaged until 3^rd passage. Viral growth was confirmed using a one-step RT-PCR targeting IBDV VP2 gene. Viral titer increased from 1^st passage through 3^rd passage. Safety was assessed in 30 specific-pathogen-free chickens (15 chickens/group) injected with 10-fold field dose of each vaccine intraocularly and monitored for 21 days. For immunogenicity and efficacy, 60 specific-pathogen-free chickens were grouped into 3 (20 chickens/group). First and 2^nd group received DF-1 cell and CEF-based IBDV vaccines, respectively. The 3^rd group served as unvaccinated control. Antibody response was measured using iELISA. Chickens were challenged 4 weeks postvaccination with very virulent IBDV (vvIBDV) intraocularly and followed-up for 10 days. Vaccination did not cause any adverse reactions during the 21 days of follow-up. In addition, both vaccines induced higher antibody titer 14 and 24 days-post-vaccination as compared to unvaccinated controls (p < 0.05). Moreover, DF-1 and CEF-based IBDV LC–75 vaccines rendered a complete protection against vvIBDV. Contrarily, morbidity and mortality in unvaccinated chickens was 50% and 30%, respectively. The results indicated that DF-1 and CEF cell-based IBDV vaccines are comparably immunogenic and efficacious. Therefore, DF-1 cell-line can be considered an affordable and convenient alternative to the CEF-based approach. The suitability of DF-1 cells to grow other IBDV strains and safety of these vaccines on bursa of Fabricius should further be investigated.

Commercial vaccines used in China do not protect against a novel infectious bursal disease virus variant isolated in Fujian

BACKGROUND

Since 2018, atrophy of the bursa has been found among vaccinated chickens with high antibody titres against infectious bursal disease virus (IBDV) in Fujian, China, suggesting poor vaccine efficacy against circulating IBDV strains.

METHODS

Novel IBDV strains were isolated, and vp2 and vp1 genes were sequenced and used to carry out phylogenetic analysis. Pathogenicity was investigated using 21-day-old specific pathogen-free (SPF) chickens. In addition, the effectiveness of current commercial vaccines used in China was evaluated against the isolated novel IBDV strains.

RESULTS

Six IBDV isolates were successfully obtained, which formed an independent cluster and belonged to genotype A2dB1, based on phylogenetic analysis of the vp2 and vp1 genes. The pathogenicity of the novel IBDV FJ2019-01 isolate in 21-day-old SPF chickens was characterised by severe atrophy of the bursa and a largely decreased number of lymphocytes, atrophy of the follicle and broadening of mesenchyme in the bursa 3-23 days after infection. Unfortunately, all vaccinated chickens with high antibody titres against IBDV also developed atrophy and largely decreased lymphocytes in the bursa, as in the unvaccinated birds challenged with FJ2019-01. Furthermore, high viral loads of FJ2019-01 were detected in the bursa of all vaccinated chickens.

CONCLUSIONS

These findings suggest that current commercial IBDV vaccines used in China did not provide protection against novel IBDV variants.

Molecular characterization of Infectious Bursal Disease Virus isolated in Chile reveals several mutations in VP2 coding region and a reassortment in its genome

Infectious Bursal Disease (IBD) is a well-described disease in young chickens. It is caused by the Infectious Bursal Disease Virus (IBDV), which has a bi-segmented, double-strand RNA genome. The absence of a lipidic envelope makes IBDV highly resistant to environmental conditions. Consequently, it is widely reported around the world. Fourteen samples retrieved from chickens exhibiting apparent alterations of the bursa of Fabricius between 2017 and 2021 were included in the study. These samples were passaged into embryonated eggs and the presence of IBD was confirmed through RT-PCR. The PCR products were sequenced and analyzed to characterize the Chilean IBDV isolates for comparison with GenBank sequences, including vaccines sequences currently used in Chile.Phylogenetic analysis classified the Chilean sequences as A1B1, except the sample 15002_CL_2021 which was classified as A2B1. On the other hand, all Chilean viruses were grouped as B1, based on viral segment B. Estimated evolutionary divergence between different genogroups supports these clustering. Moreover, samples 13936_CL_2017, 14038_CL_2017, 14083_CL_2017, 14145_CL_2018, 14431_CL_2019, and 14459_CL_2019 showed high similitude with the D78 and ViBursa CE vaccines (both currently used in Chile). Viruses 14010_CL_2018, 14040_CL_2017, 14514_CL_2019 and 14019_CL_2017 exhibited patterns that do not exactly fit either vaccine. Finally, viruses 15,041 N-_CL_2021, 15,041 N+_CL_2021, and 15004_CL_2021 showed even more differences regarding both vaccines.This is the first study in Chile to analyze the genetic sequences of IBDV isolates. The different assessments conducted as part of the study suggest a close relationship with vaccines currently in use. Interestingly, one of the viruses exhibited a reassortment in its genome segments, which could confer new characteristics to the virus. However, new approaches would be required to establish the origin of the isolated viruses, as well as how the recombination is changing its virulence or morbidity.

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.

Infectious bursal disease virus' interferences with host immune cells: What do we know?

AbstractInfectious bursal disease virus (IBDV) induces one of the most important immunosuppressive diseases in chickens leading to high economic losses due increased mortality and condemnation rates, secondary infections and the need for antibiotic treatment. Over 400 publications have been listed in PubMed.gov in the last five years pointing out the research interest in this disease and the development of improved preventive measures. While B cells are the main target cells of the virus, also other immune and non-immune cell populations are affected leading a multifaceted impact on the normally well orchestrated immune system in IBDV-infected birds. Recent studies clearly revealed the contribution of innate immune cells as well as T cells to a cytokine storm and subsequent death of affected birds in the acute phase of the disease. Transcriptomics identified differential regulation of immune related genes between different chicken genotypes as well as virus strains, which may be associated with a variable disease outcome. The recent availability of primary B cell culture systems allowed a closer look into virus-host interactions during IBDV-infection. The new emerging field of research with transgenic chickens will open up new opportunities to understand the impact of IBDV on the host also under in vivo conditions, which will help to understand the complex virus-host interactions further.

Research Note: “Hidden” infectious bursal disease virus infections in Central Europe

Infectious bursal disease virus (IBDV) is a major threat to the poultry industry globally, represented by a variety of genetic, pathogenic, and antigenic variants. The recognition of the infection may be challenging due to several factors, as the virulence of the strain, age, and immune status of the birds at infection, to name the most important ones.

Here we report about the molecular typing of IBDVs detected over the recent years in Central Europe. The results revealed the diversity of IBDV in the region, that is, very virulent strains being present in all four involved countries, the successive detection of a recently described reassortant variant in the Czech Republic, and the “rediscovery” of a subclinical pathotype virus in Hungary. These findings highlight the need for monitoring the flocks regularly not only by evaluating the production parameters but to look specifically for the occurrence of IBDV and adjust the control measures according to the results.

VP2 gene sequencing based Geno-grouping of infectious bursal disease viruses isolated from Gujarat and Maharashtra state (India)

Infectious bursal disease (IBD), caused by infectious bursal disease virus (IBDV), has recently been reported in chickens vaccinated with classical or intermediate types of vaccines from various regions of India due to the emergence of novel very virulent strains of infectious bursal disease virus (vvIBDV). In the present study, suspected samples of IBD were collected from poultry flocks of districts of Gujarat and Nagpur (Maharashtra), identified using PCR and grouped as per traditional and new genogrouping pattern. Out of 54 bursa samples, 21 (38.89%) yielded the expected amplicon of 743 bp (701-1444 bp), and were found positive for IBDV. Among these 21 positive flocks, 11 (52.38%) were already vaccinated. Upon nucleotide sequencing of amplicon and its deduction into amino acids, it was found that all the sequences of present study were related to vvIBDV according to old classification pattern. Considering the new genogrouping pattern, nine and four sequences of this study fell within G3a and G3b lineage, respectively. These sequences revealed important differences at key amino acid positions with respect to classical (G1 genogroup), variant (G2 genogroup) type of IBDV and classical vaccines. Further divergence from prototypic vvIBDV strains was revealed as, D-N at 212 position (N = 9) and 279 position (N = 1). In sequences from Maharashtra (group 2 of G3a lineage), occurrence of V instead of P/T/A at 222 position was recorded as a novel and conspicuous substitution in the immunodominant peak A of VP2 hypervariable region. Additional changes at 270 (3 sequences) and 272 positions (4 sequences) could be attributed to reverse mutation or recombination with vaccine strains. In conclusion, both point mutation and genetic reassortment with intermediate type of vaccines were found to be responsible for generation of novel vvIBDV strains in this area which belonged to G3a and G3b genogroups.

Detection and molecular characterization of a new genotype of infectious bursal disease virus in Portugal

RESEARCH HIGHLIGHTSEight IBDV strains with unique VP2 features were detected in Portugal.Based on two distinct classification methods, the strains belong to a new genotype.

Pathogenicity and molecular characterization of infectious bursal disease virus in China

Infectious bursal disease virus (IBDV) caused an acute and highly contagious infectious disease, resulting in considerable economic losses in the world poultry industry. Although this disease was well-controlled under the widely use of commercial vaccines, the novel variant IBDV strain emerged due to the highly immunized-selection pressure in the field, posting new threats to poultry industry. Here, we reported the epidemic and pathogenicity of IBDV in Hubei Province from May to August 2020. We isolated 12 IBDV strains from the broiler flocks, including 9 novel variants, 2 very virulent strains and 1 medium virulent strain. Interestingly, we identified a series of changes of amino acid sites in the VP2. Further analysis indicated that the novel variant IBDV strains caused damage to bursa of fabricius and spleen, leading to immunosuppression. Our findings underscore the importance of IBDV surveillance, and provide evidence for understanding the evolution of IBDV.

In ovo application of a live infectious bursal disease vaccine to commercial broilers confers proper immunity

Infectious bursal disease (IBD) is an economically important disease of young chickens caused by the Avibirnavirus infectious bursal disease virus (IBDV). Besides biosecurity, vaccination is the most important measure for IBDV control. Sufficient levels of maternally derived antibodies (MDA) protect against early challenge and also interfere with the take of live conventional vaccines. Recently, the field surveys conducted in four countries, published by Ashash, U., Noach, C., Perelman, B., Costello, C., Sansalone, P., Brazil, T. & Raviv, Z. [(2019). In ovo and day of hatch application of a live infectious bursal disease virus vaccine to commercial broilers. Avian Diseases, 63, 713-720] using the MB-1 vaccine strain by in ovo application or sub-cutaneous route at the day of hatch seem to conflict with the rule that very early application of a conventional live vaccine in birds with significant levels of MDA has very little chance of a successful immune response. An in ovo vaccination-challenge controlled experiment with MB-1 vaccine was performed using commercial broilers with high levels of MDA against IBDV and a vvIBDV challenge at 22 or 36 days of age. Clinical signs, bursa-bodyweight ratios, histology, serology, RT-PCR, Sanger- and deep sequencing were used to study the efficacy and safety of the in ovo-applied MB1 vaccine in comparison to an established immuno-complex vaccine. The study findings confirmed that the in ovo application of the live MB-1 vaccine in commercial broilers was successful and induced full protection against a vvIBDV challenge at 22 and 36 days of age, demonstrated by the bursa lesion score and qPCR and IBDV genotyping. Comparable to the field studies, a delayed viral replication of 2-3 weeks, following the in ovo administration of the MB1 vaccine, was observed.

The emerging naturally reassortant strain of IBDV (genotype A2dB3) having segment A from Chinese novel variant strain and segment B from HLJ 0504-like very virulent strain showed enhanced pathogenicity to three-yellow chickens

Novel variant infectious bursal disease virus (nvIBDV) is an emerging pathotype that can cause sub-clinical disease with severe, prolonged immunosuppression in young chickens. At present, two major pathotypes, including vvIBDV and nvIBDV, are prevailing in China. In this study, we propose that the nvIBDV is a new genotype (A2dB1b) and also first isolated and characterized a nvIBDV reassortant strain YL160304 (A2dB3) with segments A and B derived, respectively, from the nvIBDV and the HLJ-0504-like vvIBDV from yellow chickens in southern China. The YL160304 causes more extensive cytotropism and can infect specific-pathogen-free chicken embryos with severe subcutaneous hemorrhage. The pathogenicity of YL160304 to 4-week-old three-yellow chickens was determined and compared with those of the nvIBDV QZ191002 and the HLJ-0504-like vvIBDV NN1172. Weight gain was significantly reduced in all the challenged birds. No clinical signs and associated mortality were observed in the birds challenged with QZ191002, while the mortalities in the birds challenged with NN1172 and YL160304 were 30% (3/10) and 10% (1/10), respectively. At 7 days postchallenge, the bursa was severely damaged and the percentage of peripheral blood B lymphocyte (PBBL) decreased significantly in all the challenged birds and the quantity of the viral RNA detected in the bursa was in accordance with the results of the histomorphometry and the depletion of PBBL. This study not only confirmed the emerging epidemic of the novel variant and its reassortant strains, but also discovered that the naturally reassortant nvIBDV strain with the segment B of HLJ 0504-like vvIBDV can significantly enhance the pathogenicity to chickens.

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.

Genogrouping of Infectious Bursal Disease Viruses Circulating in Ethiopian Chickens: Proposal for Assigning Very Virulent Strains in the Country into New Sub Genogroup 3d

Introduction

In 2017 infectious bursal disease viruses (IBDVs) were reclassified into genogroups based on nature of clustering on a phylogenetic tree constructed using VP2 gene sequence data rather than according to their pathotype and/or antigenic types. Ethiopian IBD viruses were not reclassified according to the proposed genogrouping.

Methods

In order to genogroup the Ethiopian IBDVs, available VP2 gene sequences data together with reference strain sequences were retrieved from GenBank and genogrouped as recently recommended based on evolutionary tree reconstruction and determination of their clustering on the phylogenetic tree.

Results

The Ethiopian IBDVs were grouped into genogroups 1 and 3 that antigenically represent classically virulent and very virulent IBDVs, respectively. The genogroup 1 IBDVs were clustered with the vaccine strain while the genogroup 3 viruses were clustered with four known viruses belonging to sub-genogroup 3a and sub-genogroup 3b. Almost half of the Ethiopian IBDVs reported did not cluster with the specific sub-groups of genogroup 3; rather, the isolates were clustered differently suggesting they deserve a different sub-genogroup tentatively proposed as 3d. The two genogroups observed based on clustering on a phylogenetic tree were supported by corresponding deduced amino acid changes in similar positions in VP2 sequences. In addition, virulence marker amino acid genes coupled with second major hydrophilic region (amino acid positions 314–325) were predicted in these sequences that could be responsible for the occurrence of IBD outbreaks.

Conclusion

A new sub-genogroup of IBDVs, 3d, were observed in the sequences that could be one of the reasons for the frequent occurrence of IBD outbreaks and questions the protective potential of the existing vaccine. To institute disease control in the country, the effectiveness of the vaccine in use needs to be assessed in vivo against both genogroups 1 and 3 viruses and all three sub-genogroup 3 viruses circulating in the country.

A unified genotypic classification of infectious bursal disease virus based on both genome segments

Infectious bursal disease virus (IBDV) of chickens is a birnavirus with a bi-segmented double-stranded RNA genome, the segments designated as A and B. We performed phylogenetic analysis using a 366-bp fragment of segment A (nt 785-1150) and a 508-bp fragment of segment B (nt 328-835) of IBDV. A total of 463 segment A and 434 segment B sequences from GenBank, including the sequences of eight recent Bangladeshi isolates, were used in the analysis. The analysis revealed eight genogroups of segment A under serotype 1, designated as A1 (classical), A2 (US antigenic variant), A3 (very virulent), A4 (dIBDV), A5 (atypical Mexican), A6 (atypical Italian), A7 (early Australian) and A8 (Australian variant), and a single genogroup under serotype 2, designated as A0. On the other hand, segment B could be categorized into five genogroups irrespective of serotype, these being B1 (classical-like), B2 (very virulent-like), B3 (early Australian-like), B4 (Polish & Tanzanian) and B5 (Nigerian). Segment B of serotype 2 strains clustered within genogroup B1. With the bi-segmented genome of IBDV, these differences would allow for a total of 45 possible assortments. Based on the combinations of segment A and segment B genogroups observed in 463 IBDV strains, a total of 15 genotypes could be recognized. Recent Bangladeshi IBDV strains, isolated in 2016, appeared to be segment reassortants having segment A of genogroup A3 (very virulent) and segment B of genogroup B3 (early Australian-like). An extended system of nomenclature of IBDV strains is proposed.

Characterization of antigenic variant infectious bursal disease virus strains identified in South Korea

Infectious bursal disease (IBD) is one of the most important immunosuppressive diseases of young chickens, causing considerable economic losses to the poultry industry. More than 30 years ago, an antigenic variant (av) pathotype of the IBD virus (IBDV) was reported to originate in, and subsequently spread among, poultry farms in the USA. Recently, a novel avIBDV lineage was identified in China and was shown to exhibit clear differences in its pathogenicity as well as molecular characteristics compared with the previously isolated variant strains. In this study, we conducted a passive surveillance of chicken carcasses submitted to our research division from June-December 2019, and detected the IBDV strains by reverse transcription PCR. Five avIBDV strains were isolated, and their pathogenicity was determined by necropsy and molecular analysis. Additionally, a coinfection field case involving an avIBDV strain and a very virulent IBDV (vvIBDV) strain was identified. Multiple sequence alignment and phylogenetic analysis of partial viral protein 1 (VP1) and hypervariable region (hv) VP2 genes revealed that those strains originated from two different avIBDV lineages. The co-occurrence of two sub-groups of avIBDVs in South Korea confirms for the first time the evolution of antigenic variant IBDV strains, and highlights the urgency for the development of new strategies for IBDV intervention in South Korea.RESEARCH HIGHLIGHTS Five avIBDV strains were identified in South Korea by passive surveillance test in 2019.A coinfection between two IBDV strains from different genogroups was reported in a field case.By phylogenetic analysis, Korean avIBDVs belonged to two distinct lineages of antigenic variant genogroup.

Molecular Characterization of Infectious Bursal Disease Virus Isolated from Naturally Infected Broiler Chickens in Erbil, Iraq

The infectious bursal disease (IBD) is a highly contagious and immunosuppressive disease of broiler chickens and the development of a new genetic variant of the virus is responsible for major economic losses in the poultry industry. For this purpose, it was essential to isolate the molecular characterization of the virus from vaccinated broiler in Erbil, Iraq. Clinically, the infectious bursal disease is characterized by high mortality (10-15%) with hemorrhagic lesions on the breast and thigh muscles, hemorrhagic and edematous bursa of diseased chickens. In this study, the Bursa of Fabricus (BF) samples were collected between June 2018 and January 2019. Histopathological changes of the bursal sections showed existence of the cystic vacuolation of the lymphoid follicles with leukocytes infiltration as pathognomic features for IBD virus infection; and homogenates samples inoculated in chorioallantoic-membrane showed mortality in the second passage with varying degrees of hemorrhages. Agar gel precipitation test (AGPT) was positive with specific antisera. Reverse transcription polymerase chain reaction (RT-PCR) and nucleotide sequence analysis of five fragments in the hypervariable region of VP2 gene revealed transition and transversion changes. Among the five recent IBD virus isolates, the rate of identity was approximately 99% as compared with the very virulent IBD virus from Iran (ID: DQ785171.1). Phylogenetic analysis revealed that the five isolates were closely related to the Asian group with a different percentage ranged from 98-99% while it was 97% in the European group. The local isolate of the virus was registered in the Genebank under the accession number MN48052.1. In conclusion, the isolated IBDVs belong to a very virulent group. In addition, this study demonstrates the spread of this virulent virus to poultry industries in Erbil, Iraq. Further widespread surveys could help in delivering more information on the virus variability and might assist in designing novel vaccines for this pathogen.

Molecular characterization and pathogenicity of very virulent infectious bursal disease virus isolated from naturally infected turkey poults in Egypt

This study was conducted to investigate the molecular characterization and pathogenicity of very virulent infectious bursal disease virus (vvIBDV) isolated from naturally infected turkey poults and possible spread to chickens. Thirty samples were collected from turkey poults in the vicinity or in the same backyards with chickens suspected to be infected with IBDV and from live bird markets from different localities in Dakahlia governorate, Egypt. There were no obvious clinical signs in tested turkey poults except dehydration and whitish diarrhoea in some birds with no mortality, and post-mortem lesions were observed in few birds as atrophied bursae, nephritis and petechial haemorrhages on thigh muscles. Reverse transcription polymerase chain reaction (RT-PCR), histopathological examination and immunohistochemistry were used for identification of the IBDV. Out of 30 tested samples, 17 samples (56.7%) were positive by RT-PCR. Phylogenetic analysis of VP2 gene of two selected IBDV strains (turkey 1 and turkey 2) showed a close genetic relationship to vvIBDV strains (serotype 1) isolated from chickens in Egypt and other countries with 93.1 to 95.99% identity for turkey 1 strain and 95.54 to 98.51% for turkey 2 strain. Both turkey 1 and turkey 2 strains were closely related to the Nigerian vvIBDV strain isolated from turkeys with 95.78% and 96.37% identity, respectively. Sequence analysis of both strains demonstrated that they have conserved amino acid residues of vvIBDV (I242, I294 and S299) and Y220F amino acid substitution which is very common in Egyptian vvIBDV chicken strains, while Turkey 1 strain has amino acid substitutions at A222P and I256V. Histopathological examination showed marked depletion of bursal lymphoid tissue. In conclusion, for the first time in Egypt, the molecular characterization and pathogenicity confirmed the presence of natural infection of turkey poults with vvIBDV (serotype 1) with possible spread to chickens causing severe economic losses.

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.

Infectious Bursal Disease Virus: Molecular Epidemiologic Perspectives and Impact on Vaccine Efficacy Against Avian Influenza and Newcastle Disease Viruses

Infectious bursal disease (IBD) virus (IBDV) is the causative agent of a highly contagious and immunosuppressive disease of chickens with huge economic losses to the poultry industry despite extensive vaccination. Analysis of isolated IBDV field strains from vaccinated birds would greatly improve the current immunization regimens and support the development of vaccines that offer better immunity. The study investigated the genetic characteristics and pathologic features of IBDVs in commercial broiler chicken farms, as well as the effect of IBDV infection on the efficacy of vaccination against avian influenza virus (AIV) and Newcastle disease virus (NDV) under field conditions. A preliminary diagnosis of IBD was made on the basis of the flock history and the characteristic gross pathologic findings. Microscopically, lymphoid depletion in bursal follicles with infiltration of lymphomononuclear cells along with cystic cavitations reflected the IBDV infection. The molecular analysis confirmed the IBDV infection in (57.1%) of tested flocks. Upon phylogenetic analysis of the VP2 hypervariable region of 14 Egyptian IBDVs, most viruses (n = 12) were clustered within the genogroup 3, while two viruses were closely related to attenuated vaccine isolates in genogroup 1. The analysis of the amino acid (aa) sequences revealed that most of the strains possessed five consistent aas at the VP2 protein (222A, 242I, 256I, 294I, and 299S), which are characteristic for the very virulent IBDV (vvIBDV). Serology indicated the immunosuppressive effect of IBDV, which is represented by a decrease (1.6-2.6 and 1.4-2.6 mean log ₂) in the hemagglutination inhibition titer of the low pathogenic AIV subtype H9N2 and NDV, respectively. The examined IBDVs showed a high mutation rate within the hypervariable domain of the VP2 peptide. The results highlighted the need for carrying out an inclusive surveillance of IBDV infections in chicken flocks in Egypt.

Occurrence and spread of a reassortant very virulent genotype of infectious bursal disease virus with altered VP2 amino acid profile and pathogenicity in some European countries

Reassortant strains of Infectious Bursal Disease Virus (IBDV) were detected in commercial broiler flocks in the Netherlands, Belgium, Denmark, Czech Republic and Germany and in layers and organic broilers in Sweden in the period of 2017-19. Genetic analysis, based on hypervariable region of VP2 gene showed grouping together with very virulent IBDV strains (vvIBDV, Genogroup 3), but these recent viruses formed a separate cluster, which was most closely related to Latvian IBDV strains from 2010-13. VP1 gene of these isolates was most closely related to D78 attenuated IBDV strain. The recently described reassortant IBDV strain (Bpop/03/PL) from Poland with similar genomic constellation (segment A from vvIBDV, segment B from attenuated strain) retained its pathogenicity (80 % mortality in SPF chickens). Infection with the North-West European reassortant IBDVs described in this study showed subclinical feature in the field (without complicating agents) and when tested under standardized pathogenicity test in SPF layer chickens (no mortality or clinical signs, but marked bursa atrophy was observed). Although these recent North-West European reassortant strains had all amino acid residues in their VP2 gene which are considered as markers of vvIBDV strains, they exhibited typical amino acid changes compared to vvIBDV reference strains that should contribute to the determination of pathogenicity. Diagnostic investigations indicated that co-infection with fowl adenovirus or chicken infectious anaemia virus exaggerated the outcome of the IBDV infection (10-20 % mortality). Widespread presence of this reassortant IBDV group in clinically healthy flocks draws attention to the importance of active surveillance.

Naturally occurring cell-adapted classic strain of infectious bursal disease virus

Infectious bursal disease virus (IBDV), the etiological agent of infectious bursal disease (IBD), is a variable RNA virus of Avibirnavirus. Some artificially attenuated vaccine strains of IBDV can adapt to cell culture of chicken embryo fibroblast (CEF) cell or its immortalized cell line DF1 in vitro while wild-type IBDV cannot. In this study, for the first time, a naturally occurring cell-adapted classic strain (genogroup 1) of IBDV named IBD17JL01 was identified in China. Animal experiments showed that IBD17JL01 could severely damage the central immune organ of infected chickens. Sequence analysis of the full-length genome revealed the peculiar molecular characteristics of IBD17JL01 with a few amino acid substitutions that might be involved in cell-tropism, antigenicity, and virulence of IBDV. Identification of this novel strain is beneficial to our understanding of the complexity of the epidemiology of IBDV. And the expansion of viral cell-tropism might increase the potential risk of the reassortment of different IBDVs including the live vaccines.

Research Note: Detection of infectious bursal disease virus antibodies in free-living wild birds in Zaria, Nigeria

Infectious bursal disease virus (IBDV) is an immunosuppressive pathogen of poultry causing great economic losses to the poultry industry. In this study, the IBDV antibodies were detected in captured free-living wild birds in Zaria, Nigeria. One hundred and fifty free-living wild birds, comprising 30 birds each of 5 different species, were sampled over a period of 9 months. Blood samples were collected from each bird, and harvested sera were tested for IBDV antibodies using enzyme-linked immunosorbent assay. Results indicated IBDV seroprevalences in speckled pigeon (6.67%) and cattle egret (3.33%). In conclusion, the detection of IBDV antibodies in free-living wild birds in this study is indicative of previous natural exposure of these birds to the virus. These species of wild birds could therefore serve as carriers of these viruses and, consequently, transmit these viruses to chickens.

Comparative in vivo pathogenicity study of an ITA genotype isolate (G6) of infectious bursal disease virus

Recently, a new genotype of infectious bursal disease virus (IBDV), named ITA, was detected in IBD-vaccinated Italian broilers. Genome characterization revealed ITA to be a genetically different IBDV, belonging to genogroup 6 according to a recently proposed IBDV classification. The currently available clinical data do not allow any definition of the degree of pathogenicity of the ITA-IBDV isolates. In the present study, a pathogenicity trial was conducted by the oral inoculation of specific-pathogen-free (SPF) chickens. Birds were housed in poultry isolators and inoculated at 35 days of age with an ITA-IBDV isolate (35 birds) or a strain belonging to the G1a genogroup as a comparison (35 birds). Control birds (25 birds) were contextually mock-inoculated with sterile water. Birds were observed daily for clinical signs and at 0, 7, 14, 21 and 28 days post-inoculation (dpi) were bled for IBDV antibody detection. At 2, 4, 7, 14, 21 and 28 dpi, five birds from each of the inoculated groups, and three from the control group, were euthanized and subjected to a post-mortem examination; the bursa:body weight and thymus:body weight ratios were calculated. Microscopic lesions of the bursa and thymus were scored on the basis of lymphoid necrosis and/or depletion or cortex atrophy, respectively. Both viruses induced a subclinical course of disease, as neither clinical signs nor mortality were recorded during the study, even in the presence of typical IBDV gross and microscopic lesions. Bursal damage, measured by the bursa:body weight ratio, was more noticeable and precocious after ITA-IBDV inoculation. Histopathology scores of the bursa, indicative of rapid lymphoid depletion, confirmed the aggressiveness of the ITA-IBDV strain in this organ. This study showed that, although the ITA-IBDV strain tested causes infection with a subclinical course, it induces severe damage to lymphoid tissues. Therefore, its circulation in birds might be a threat for the poultry industry and may jeopardize the success of the production cycle.

Complete genome analysis and time scale evolution of very virulent infectious bursal disease viruses isolated from recent outbreaks in Morocco

Emerging of very virulent infectious bursal disease virus (vvIBDV) genotype in poultry flocks in Morocco were characterized. VP2 sequence analysis showed that the strains of Moroccan vvIBDV genotypes clustered separately from classic and vaccine strains reference of IBDV. The full-length genome of four Moroccan vvIBDV strains was determined, in order to get a more exhaustive molecular characterization allowing to conduct the evolution time scale and speculations on their origin. In a phylogenetic tree, nucleotide sequences of segment A and B formed a common branch with those vvIBDV references strains published in GenBank, but they clearly grouped into a distinct subcluster. An alignment of deduced amino acid sequences segment B, confirmed the presence of the conserved TDN tripeptide found in all of the vvIBDV genotype and revealed the presence of 2 substitutions I472L and E688D specific for the vvIBDV Moroccan isolates. The deduced amino acid sequences of segment A genes showed the presence of the "signature" typical of the vvIBDV genotype and revealed the presence of 7 aa substitutions specific for the vvIBDV Moroccan strains. The evolution rate for IBDV VP2 gene was estimated at 5.875 × 10^-4 substitutions/site/year. The estimation of the time to most common recent ancestor of Moroccan vvIBDV based on the VP2 sequences available was 31 years, corresponding to 3 years earlier than the first vvIBDV case detection in layers in the country.

Identificación de genogrupos del virus de la Enfermedad de Gumboro en granjas avícolas en Colombia

El virus de la enfermedad de Gumboro (IBDV) es un avibirnavirus con genoma dsARN que presenta altas tasas de mutación y recombinación. A pesar del efecto inmunosupresor en aves y la frecuencia con que ocurre la infección por este agente en el país son pocos los estudios que caracterizan los cuadros clínicos y se desconoce cuáles son los genogrupos circulantes. Esta investigación tuvo como objetivo determinar la frecuencia de lesiones histopatológicas en órganos del sistema inmune e identificar los genogrupos del IBDV en aves comerciales de Colombia. Para determinar la frecuencia de presentación de lesiones en órganos del sistema inmune se analizaron 381 casos clínicos de las bases de datos del Laboratorio de Patología Aviar (LPA) de la Universidad Nacional de Colombia, sede Bogotá (periodo 2016-2018). Asimismo, se secuenciaron los productos de RT-PCR del gen que codifica para la proteína viral VP2 provenientes de 35 muestras de bursas de Fabricio. Como resultado se encontró evidencia de lesiones microscópicas compatibles con procesos de inmunodepresión en órganos del sistema inmune (bursa de Fabricio, timo, bazo y médula ósea) en el 25 % (97) de los casos analizados y se identificaron los genogrupos 1, 2 y 4 en la siguiente proporción: genogrupo 1-69 % (virus clásicos), genogrupo 2-25 % (variantes) y genogrupo 4-6 % (identificado en Suramérica). Estos hallazgos demuestran la presencia de lesiones en órganos del sistema inmune y la existencia de los genogrupos 1, 2 y 3 del IBDV circulando en aves comerciales en Colombia. Esta es la primera investigación en el país con este sistema de clasificación que permite evidenciar con mayor precisión los cambios en el genoma del IBDV. Lo anterior señala la necesidad de continuar con este tipo de estudios para tener una mejor comprensión de la infección en campo y orientar el diseño e implementación de estrategias de control.

Virus-Induced Immunosuppression in Chickens

A healthy immune system is a cornerstone for poultry production. Any factor diminishing the immune responses will affect production parameters and increase cost. There are numerous factors, infectious and noninfectious, causing immunosuppression (IS) in chickens. This paper reviews the three viral diseases that most commonly induce IS or subclinical IS in chickens: Marek's disease virus (MDV), chicken infectious anemia virus (CIAV), and infectious bursal disease virus (IBDV), as well as the interactions among them. MDV-induced IS (MDV-IS) affects both humoral and cellular immune responses. It is very complex, poorly understood, and in many cases underdiagnosed. Vaccination protects against some but not all aspects of MDV-IS. CIAV induces apoptosis of the hemocytoblasts resulting in anemia, hemorrhages, and increased susceptibility to bacterial infections. It also causes apoptosis of thymocytes and dividing T lymphocytes, affecting T helper functions, which are essential for antibody production and cytotoxic T lymphocyte (CTL) functions. Control of CIAV is based on vaccination of breeders and maternal antibodies (MAbs). However, subclinical IS can occur after MAbs wane. IBDV infection affects the innate immune responses during virus replication and humoral immune responses as a consequence of the destruction of B-cell populations. Vaccines with various levels of attenuation are used to control IBDV. Interactions with MAbs and residual virulence of the vaccines need to be considered when designing vaccination plans. The interaction between IBDV, CIAV, and MDV is critical although underestimated in many cases. A proper control of IBDV is a must to have proper humoral immune responses needed to control CIAV. Equally, long-term control of MDV is not possible if chickens are coinfected with CIAV, as CIAV jeopardizes CTL functions critical for MDV control.

Inoculation of specific pathogen-free chickens with an infectious bursal disease virus of the ITA genotype (G6) leads to a high and persistent viral load in lymphoid tissues and to a delayed antiviral response

Infectious Bursal Disease Virus (IBDV) of the ITA genotype (G6) was shown to have peculiar molecular characteristics and, despite a subclinical course, aggressiveness towards lymphoid tissues after experimental infection of specific-pathogen-free (SPF) chickens. The aim of the present study was to evaluate and compare with a Classical IBDV strain, ITA IBDV distribution and persistence in various tissues (bursa of Fabricious, spleen, thymus, bone marrow, caecal tonsils, Harderian gland, kidney, liver and proventriculus), its cloacal shedding and the involvement of gut TLR-3 in duodenum tissues. The 35-day-old SPF chickens were experimentally infected and sampled up to 28 days post infection (dpi) for IBDV detection and TLR-3 quantification by qRT-PCR. The ITA IBDV strain was detected in lymphoid and most non-lymphoid tissues up to the end of the trial, with higher loads compared to the Classical IBDV. Most of those differences were found during the first 2 weeks post-infection. Notably, bone marrow and caecal tonsils presented higher viral loads until 28 dpi, allowing to speculate that these organs may serve as non-bursal lymphoid tissues supporting virus replication. Differences in relative TLR-3 gene expression between ITA IBDV-infected birds and Classical-IBDV infected ones were observed at 4, 14 and 21 dpi, being initially higher in Classical group and later in ITA group. Our results provide new insights into IBDV pathogenesis showing that IBDV of ITA genotype leads to a high and persistent viral load in lymphoid tissues and to a delayed antiviral response.

Molecular characterization of field isolates of infectious bursal disease virus from three decades, 1987-2018, reveals a distinct genotypic subgroup in Vietnam

The complete nucleotide sequence of the viral protein 2 (VP2) ORF was determined for 26 Vietnamese infectious bursal disease isolates collected from clinical outbreaks in vaccinated flocks from 1987 to 2018 and two commercial vaccine specimens. These sequences were compared for molecular classification with 42 reference strains representing all four main classes of serotype 1, including very virulent (vvIBDV), classical (cvIBDV), antigenic variant (avIBDV) and attenuated (atIBDV) strains, and serotype 2 strains. Amino acids at nine key positions in the VP2-HVR in 20 Vietnamese isolates, A222, I242, Q253, I256, D279, A284, I294, S299, A329, which are typical of the vvIBDV class, were found to be identical in all of the isolates. Eighteen of these isolates had a unique change at residue 212 (D212N) located in the P_AB loop. Phylogenetic analysis revealed a distinct lineage/subclade with strong nodal support (96%) that included recent Chinese IBDV strains that were distinct from typical vvIBDVs. Six isolates contained the amino acid substitutions P222, V242, Q253, V256, D279, A284, I294, N299, A329, which are present in two vaccine strains derived from strain 2512 and these isolates were also closely related to the classical virulent STC strain. Data from this study show that there is considerable genetic diversity among vvIBDVs, which vary according to geographic region. Antigenic drift and differences in genetic characteristics between virulent strains and IBDV vaccine strains may be the cause of vaccine failure. Better antigenic matching of vaccines to the strains circulating in Vietnam is therefore required.

Molecular epidemiology of endemic and very virulent infectious bursal disease virus genogroups in backyard chickens in California, 2009-2017

Pathogenic strains of infectious bursal disease virus (IBDV) are associated with increased morbidity, mortality, and immunosuppression in susceptible chickens. Backyard poultry is increasing in popularity in the United States, but very little is known about the prevalence and molecular epidemiology of IBDV within these flocks. We performed a retrospective study and phylogenetic analyses of IBDV detected in backyard chickens (BYCs) submitted to the California Animal Health and Food Safety (CAHFS) diagnostic laboratory system in 2009-2017. There were 17 CAHFS autopsy cases of very virulent IBDV (vvIBDV) segment A detected by RT-rtPCR in BYC flocks from 7 counties in California from 2009-2017. During this same time period, non-vvIBDV genotypes were detected by RT-rtPCR in 16 autopsy cases originating from BYC premises in 10 counties in California. Subsequent RT-PCR and phylogenetic analysis of a segment of the hvVP2 and VP1 gene identified vvIBDV, interserotypic reassortant IBDV (vvIBDV segment A and serotype 2 segment B), and non-vvIBDV (variant/subclinical IBDV and classic IBDV) strains in BYC flocks in California.

Antigenicity, pathogenicity and immunosuppressive effect caused by a South American isolate of infectious bursal disease virus belonging to the "distinct" genetic lineage

Infectious bursal disease virus (IBDV) is the causative agent of a highly contagious immunosuppressive disease affecting young chickens. The recently described "distinct IBDV" (dIBDV) genetic lineage encompasses a group of worldwide distributed strains that share conserved genetic characteristics in both genome segments making them unique within IBDV strains. Phenotypic characterization of these strains is scarce and limited to Asiatic and European strains collected more than 15 years ago. The present study aimed to assess the complete and comprehensive phenotypic characterization of a recently collected South American dIBDV strain (1/chicken/URY/1302/16). Genetic analyses of both partial genome segments confirmed that this strain belongs to the dIBDV genetic lineage and that it is not a reassortant. Antigenic analysis with monoclonal antibodies indicated that this strain has a particular antigenic profile, similar to that obtained in a dIBDV strain from Europe (80/GA), which differs from those previously found in the traditional classic, variant and very virulent strains. Chickens infected with the South American dIBDV strain showed subclinical infections but had a marked bursal atrophy. Further analysis using Newcastle disease virus-immunized chickens, previously infected with the South American and European dIBDV strains, demonstrated their severe immunosuppressive effect. These results indicate that dIBDV strains currently circulating in South America can severely impair the immune system of chickens, consequently affecting the local poultry industry. Our study provides new insights into the characteristics and variability of this global genetic lineage and is valuable to determine whether specific control measures are required for the dIBDV lineage. Research Highlights A South American strain of the dIBDV lineage was phenotypically characterized. The strain produced subclinical infections with a marked bursal atrophy. Infected chickens were severely immunosuppressed. The dIBDV strains are antigenically divergent from other IBDV lineages.