Genetic characterization of South American infectious bursal disease virus reveals the existence of a distinct worldwide-spread genetic lineage

Genomic characterization of infectious bursal disease virus in Argentina provides evidence of the recent transcontinental spread of Chinese genotype A2dB1b

The infectious bursal disease virus (IBDV) is a significant pathogen affecting the poultry industry worldwide. Its epidemiological history has been marked by the emergence of strains with different antigenic, pathogenic, and genetic features, some of which have shown notable spread potential. The A2dB1b genotype, also known as novel variant, has become widespread and gained increased relevance in IBDV epidemiology. This genotype was described in China in the 2010s and rapidly spread in Asia and Africa. The present study describes the circulation of the A2dB1b genotype in Argentina. Applying a next-generation sequencing approach, we obtained the complete coding sequence of 18 Argentine viruses. The high level of genomic homogeneity observed amongst these viruses, their monophyletic clustering in both partial and complete segments A and B derived phylogenies, and their close relatedness to some Chinese strains suggest that a unique transcontinental spread event from China to Argentina occurred recently. The apparent success of the A2dB1b genotype spreading throughout Asia, Africa, and South America may partially be due to specific amino acid characteristics. Novel residues in the hypervariable region of VP2 may help A2dB1b IBDVs evade the protection elicited by the applied commercial vaccines. Our findings underscore the importance of continuous characterization of field samples and evaluation of the control measures currently applied to fight against this specific IBDV genotype.

Evasion of maternal antibody protection by an IBDV Argentine variant

Infectious bursal disease (IBD) is a viral disease that affects the ability of chickens to produce humoral immune responses. One way to prevent the disease is the passage of maternally derived antibodies (MDA) from dams to offsprings via the yolk. Despite sanitary measures, which include immunization with genogroup 1 (G1) vaccines, infections with IBDV genogroup 4 (G4) in young animals have been detected. The aim of this study was to determine whether a local IBDV isolate belonging to G4 could evade the immunity generated by MDAs. Twelve-day-old animals positive for MDA, were inoculated with G1 or G4 isolates or phosphate buffered saline (PBS) as a control. After 1 wk, the animals were sacrificed and the following parameters were evaluated: bursa-body (BB) ratio, viral load, and histologic damage in the bursa of Fabricius. Results showed that G4-infected animals had significant differences in the BB ratio compared to the PBS group. In addition, viral load was significantly higher in the G4 group than in the G1 group. Histologic damage in the bursa of Fabricius was detected only in G4-infected MDA chickens. Our results suggest that infection with G4 local isolate can circumvent the immunity generated by MDA and, furthermore, that G4 isolate does not differ in its pathogenicity from G1 isolate, which underlines the need to include variant strains in vaccine formulations to reduce potential losses caused by these viruses.

Molecular epidemiology of infectious bursal disease virus in the Near East and Persian Gulf regions

RESEARCH HIGHLIGHTS

Different field IBDVs were found to circulate in the Near and Middle East.Multiple atypical genotypes (A3B1, A4B1, A6B1) were found to circulate extensively.Traditional very virulent IBDVs (A3B2) were a minority of the detected strains.Viral exchanges can be hypothesized between the region and different continents.

First Detection and Molecular Characterization of Novel Variant Infectious Bursal Disease Virus (Genotype A2dB1b) in Egypt

Infectious bursal disease (IBD) is an immunosuppressive disease causing significant damage to the poultry industry worldwide. Its etiological agent is infectious bursal disease virus (IBDV), a highly resistant RNA virus whose genetic variability considerably affects disease manifestation, diagnosis and control, primarily pursued by vaccination. In Egypt, very virulent strains (genotype A3B2), responsible for typical IBD signs and lesions and high mortality, have historically prevailed. The present molecular survey, however, suggests that a major epidemiological shift might be occurring in the country. Out of twenty-four samples collected in twelve governorates in 2022-2023, seven tested positive for IBDV. Two of them were A3B2 strains related to other very virulent Egyptian isolates, whereas the remaining five were novel variant IBDVs (A2dB1b), reported for the first time outside of Eastern and Southern Asia. This emerging genotype spawned a large-scale epidemic in China during the 2010s, characterized by subclinical IBD with severe bursal atrophy and immunosuppression. Its spread to Egypt is even more alarming considering that, contrary to circulating IBDVs, the protection conferred by available commercial vaccines appears suboptimal. These findings are therefore crucial for guiding monitoring and control efforts and helping to track the spread of novel variant IBDVs, possibly limiting their impact.

A rapid and affordable amplicon-based method for next-generation genome sequencing of the infectious bursal disease virus

The infectious bursal disease virus (IBDV) causes a severe immunosuppressive disorder in young chickens. IBDV evolution resulted in the emergence of strains with divergent genetic, antigenic, and pathogenic characteristics. Genetic classification is typically performed by sequencing the coding region of the most immunogenic region of the viral protein 2 (VP2). Sequencing both double-stranded RNA genome segments is essential to achieve a more comprehensive IBDV classification that can detect recombinants and reassortments. Here, we report the development and standardization of a tiled PCR amplicon protocol for the direct and cost-effective genome sequencing of global IBDV strains using next-generation technology. Primers for tiled PCR were designed with adapters to bypass expensive and time-consuming library preparation steps. Sequencing was performed on Illumina MiniSeq equipment, and fourteen complete genomes of field strains were assembled using reference sequences. The PCR-enrichment step was used to obtain genomes from low-titer biological samples that were difficult to amplify using traditional sequencing. Phylogenetic analyses of the obtained genomes confirmed previous strain classification. By combining the enrichment methodology with massive sequencing, it is possible to obtain IBDV genomic sequences in a fast and affordable manner. This procedure can be a valuable tool to better understand virus epidemiology.

Study of coinfection with local strains of infectious bursal disease virus and infectious bronchitis virus in specific pathogen-free chickens

Immunosuppressive diseases cause great losses in the poultry industry, increasing the susceptibility to infections by other pathogens and promoting a suboptimal response to vaccination. Among them, infectious bursal disease virus (IBDV) arises as one of the most important around the world. IBDV infects immature B lymphocytes, affecting the immune status of birds and facilitating infections by other pathogens such as avian infectious bronchitis virus (IBV). Although it has been reported that the interaction between these viruses increases IBV clinical signs, there are no actual studies about the interaction between regional circulating isolates that validate this statement. In this context, the objective of our work was to evaluate the effect of the interaction between local isolates of IBDV (belonging to genogroup 4) and IBV (lineage GI-16) in chickens. Thus, specific pathogen-free chickens were orally inoculated with IBDV genogroup (G) 4 or with PBS at 5 d of age. At 14-days postinoculation (dpi) the animals were intratracheally inoculated with a GI-16 IBV or with PBS. At multiple time points, groups of birds were euthanized and different parameters such as histological damage, viral load, lymphocyte populations and specific antibodies were evaluated. The success of IBDV infection was confirmed by the severity of bursal atrophy, viral detection, and presence of anti-IBDV antibodies. In IBV-infected animals, the presence of viral genome was detected in both kidney and bursa. The coinfected animals showed higher degree of lymphocyte infiltration in kidney, higher rate of animals with IBV viral genome in bursa at 28 dpi, and a clear decrease in antibody response against IBV at 28, 35, and 40 dpi. The results indicate that the infection with the local isolate of IBDV affects the immune status of the chickens, causing major severe damage, in response to IBV infection, which could consequently severely affect the local poultry industry.

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.

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

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

Efficacy of live attenuated, vector and immune complex infectious bursal disease virus (IBDV) vaccines in preventing field strain bursa colonization: A European multicentric study

Infectious bursal disease virus (IBDV) is among the most relevant and widespread immunosuppressive agents, which can severely damage poultry farming by causing direct losses, predisposing the host to secondary diseases and reducing the efficacy of vaccination protocols against other infections. IBDV has thus been the object of intense control activities, largely based on routine vaccination. However, the need for protecting animals from the infection in the first period of the production cycle, when the bursa susceptibility is higher, clashes with the blanketing effect of maternally derived antibodies. To overcome this issue, other strategies have been developed besides live attenuated vaccines, including vector vaccines and immune complex (icx) ones. The present study aims to investigate, in field conditions, the efficacy of these approaches in preventing IBDV infection in laying chickens vaccinated with either live attenuated, vector or immune complex (icx) vaccines. For this purpose, a multicentric study involving 481 farms located in 11 European countries was organized and IBDV infection diagnosis and strain characterization was performed at 6 weeks of age using a molecular approach. Vaccine strains were commonly detected in flocks vaccinated with live or icx vaccines. However, a significantly higher number of field strains (characterized as very virulent IBDVs) was detected in flocks vaccinated with vector vaccines, suggesting their lower capability of preventing bursal colonization. Different from vector vaccines, live and icx ones have a marked bursal tropism. It can thus be speculated that vaccine virus replication in these sites could limit vvIBDV replication by direct competition or because of a more effective activation of innate immunity. Although such different behavior doesn't necessarily affect clinical protection, further studies should be performed to evaluate if vvIBDV replication could still be associated with subclinical losses and/or for viral circulation in a “vaccinated environment” could drive viral evolution and favor the emergence of vaccine-escape variants.

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.

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.

Genetic variability in VP1 gene of infectious bursal disease virus from the field outbreaks of Kerala, India

Infectious bursal disease (IBD) is considered as menace as it affects poultry industry globally causing immunosuppression, high mortality and heavy economic loss. Outbreaks of IBD were reported in many states of India including Kerala. VP1 gene acts as an important factor in the process of virus encapsidation and its involvement in viral virulence and viral replication indicates its importance in infectious bursal disease virus (IBDV). The present study was conducted to carry out the molecular characterization of VP1 gene of virulent IBDV in Kerala. A total of 42 samples were processed for the detection and analysis of VP1 gene of IBDV. Out of 42 samples, 21 samples were positive for VP1 gene of IBD. The phylogenetic analysis of the partial VP1 gene sequences reveals the clustering of IBDV isolates into very virulent IBDV (vvIBDV) and non-virulent IBDV (vIBDV). Eighteen isolates (11 isolates from vaccinated flock and 7 from non-vaccinated flocks) clustered with very virulent strains. Three isolates (2 isolates were from vaccinated flock and 1 from non-vaccinated flock) clustered with non-virulent IBDV strains, showing more evolutionarily similarity to south Indian strain VCN14/ABT/MVC/India. It is observed that vvIBDV isolates from this study have common ancestor with the south Indian strain PY12 but showed 9-10% divergence from this strains. The amino acid analysis of these 21 isolates revealed that 17 isolates possessed the characteristic vvIBDV TDN amino acid triplet, while the three isolates had non-vIBDV NEG amino acid triplet at 145/146/147 position. The remaining isolate 1/CVASP/IBDV/VP1 shows unique PDN triplet instead of TDN. Two vvIBDV isolates (15/CVASP/IBDV/VP1 and 18/CVASP/IBDV/VP1) showed 100% nucleotide and amino acid similarity with intermediate plus vaccine strain. Four vvIBDV isolates showed neutral amino acid substitution K251R which was earlier reported in Indian strains but first time in south Indian isolates. The most common unique amino acid substitution observed in our study was neutral E269D amino acid substitution in 12 isolates, neutral amino acid substitution T329S in five isolates, neutral T174N and non-polar to polar amino acid substitution A178T in isolate 10/CVASP/IBDV/VP1, non-polar to polar amino acid substitution P360R in isolate 17/CVASP/IBDV/VP1 and non-polar to polar amino acid substitution P188S in isolate 1/CVASP/IBDV/VP1. These novel mutations in our study reveal the role of genetic drift in the evolution of vvIBDV strains. The isolate 2/CVASP/IBDV/VP1 from non-vaccinated flock shows VP1 gene of non-vIBDV, but possessing VP2 of vvIBDV type indicates this is evolved by genetic shift of segments A and B. This is the first genetic characterization study of field VP1 gene of IBDV isolates in Kerala, India.

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.

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.

Origin and global spreading of an ancestral lineage of the infectious bursal disease virus

Infectious bursal disease virus (IBDV) is an economically relevant and widespread pathogen that produces immunosuppression in young chickens. IBDV is genetically classified into seven genogroups (G1-G7), where the traditional classic, variant and very virulent strains correspond to G1, G2 and G3, respectively. The G4 strains, also known as 'distinct' (dIBDV), have recently acquired increased relevance because of their prevalence and notorious impair to the poultry industry in South America. Here, worldwide dIBDV strains were studied using phylogenetic and phylodynamic approaches. The phylogenetic analyses performed using partial and complete sequences of both viral segments (A and B) consistently clustered the dIBDV strains in a monophyletic group. The analyses of the VP5, polyprotein and VP1 coding regions identified amino acid residues that act as markers for the identification of the entire dIBDV group or different sub-populations. The phylodynamic analyses performed using the hypervariable region of VP2 indicated that the dIBDV strains emerged in the early 1930s in Eastern Europe, shortly after the emergence of classic strains (1927) and before variant (1949) and very virulent strains (1967). The analysis of the migration routes indicated that after its emergence, the dIBDV strains spread to Eastern Asia around 1959, to Brazil around 1963, and to Argentina around 1990. These inter-continental migrations resulted in three sub-populations that are currently represented by strains from (a) Brazil, (b) Eastern Asia and Canada, and (c) Eastern Europe, Argentina and Uruguay. Taken together, our results highlight the complex evolutionary history of IBDV and the importance of new phylodynamic data to unravel and nearly follow the different evolutionary pathways taken by this important poultry pathogen.

Genetic Characterization of Infectious Bursal Disease Viruses from Field Outbreaks of the North East Region of India

In recent years, acute severe outbreaks of infectious bursal disease (IBD) are frequently observed in commercial chicken populations of the North East Region (NER) of India, resulting in huge economic loses to poultry farmers. Field outbreaks of IBD in 30 different poultry farms in the NER were confirmed by clinicopathologic examination and reverse transcriptase PCR. A total of 10 isolates of IBD virus (IBDV) from these outbreaks were characterized by the genetic analysis of VP1 and the hypervariable region of the VP2 gene. Nucleotide sequences, deduced amino acid sequences, and phylogenetic analysis of both VP2 and VP1 genes revealed two genetically diverse strains of very virulent IBDV (vvIBDV) and one intermediate strain circulating in the NER. These isolates differ at nucleotide and amino acid levels from vvIBDV isolates of mainland India and are clustered in distinctly separate groups in the phylogenetic tree. Six of the isolates revealed a unique combination of vvIBDV amino acid signatures in the VP2 gene (A222, I256, I294), while bearing the non-vvIBDV amino acid signatures of the VP1 gene (146E, 147G, 242D), but they are clearly classified as vvIBDV in a phylogenetic analysis of both genes. Interestingly, one of the isolates showed 99% sequence homology with attenuated vaccine strains in the VP2 gene and clustered together. This study demonstrates the diversity of IBDVs in India and document for the first time the possible involvement of attenuated vaccine strains in the epidemiology of IBD in India.

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.

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.

Phylodynamic analyses of Brazilian antigenic variants of infectious bursal disease virus

Infectious bursal disease virus (IBDV) is a very important pathogen to poultry production and it is classified into three main groups: classical virulent (cvIBDV), very virulent (vvIBDV) and antigenic variants (avIBDV). This last group is composed by five different genetic lineages (recently classified in genogroups G2, G4, G5, G6, and G7) distributed in specific regions around the world. Brazil is one of the biggest poultry producers in the world and the present study aimed to investigate the evolutionary history of avIBDVs of the genogroup G4 in Brazil. A total of 5331 IBDV positive bursa samples, from different Brazilian poultry flocks, were genotyped in a period of ten years (2005 to 2014) and 1888 (35.42%) were identified as local avIBDVs. The highly variable region of the viral protein 2 (hvvp2) gene of 28 avIBDVs was sequenced and used in phylogenetic analyses and evaluation of local amino acid signatures. In addition, all complete and partial IBDV vp2 gene sequences, with local and year of collection information available on GenBank, were retrieved. Phylogenetic analyses were carried out based on a maximum likelihood method for the classification of genogroups occurring in Brazil. Based on a Maximum Likelihood (ML) phylogenetic tree, all Brazilian avIBDVs grouped into the genogroup 4. Bayesian phylodynamics analysis demonstrated the ancestor virus of this group was probably introduced in South America in 1968 (1960 to 1974, 95% HPD) and in Brazil in 1974 (1968 to 1977, 95% HPD) and the most likely source was East Europe (Hungary or Poland). All Brazilian avIBDV sequences, as well as the other genogroup 4 sequences, showed a specific pattern of amino acid: S222, T272, P289, I290, and F296. This report brings new insights about the IBDV epidemiology in Brazil and South America.

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.

Development of real-time PCR assays for single and simultaneous detection of infectious bursal disease virus and chicken anemia virus

Infectious bursal disease virus (IBDV) and chicken anemia virus (CAV) cause relevant immunosuppressive diseases in poultry. Clinical diagnosis of these viruses is challenging given the different disease presentations and the frequent occurrence of co-infections with other pathogens. Here, we standardized and validated simplex and duplex RT-qPCR assays for the straightforward detection of IBDV and CAV. The qPCR assays are based on primers and hydrolysis probes that target highly conserved regions of IBDV and CAV genomes. Analytical sensitivity tests on 10-fold serial dilutions containing 10⁰-10⁸ viral genomes indicated that the simplex assays have good determination coefficients and efficiency and detect a wide range of virus doses (10² to 10⁸ molecules copies/reactions). The relatively small values of intra- and inter-assay variability ensure the repeatability and support its reproducibility in different diagnostic and research facilities. The assays are also efficient tools for absolute quantification as indicated by the analytical performance analysis. The assays have an excellent specificity and absence of cross-reactivity with negative samples, or with other common avian viruses. The simplex IBDV and CAV assays use probes labelled with different dyes (FAM and HEX) and can be multiplexed for the simultaneous detection of both viruses. The determination coefficients, PCR efficiencies, and relatively small intra- and inter-assay variability were comparable to the simplex assays. This duplex assay is the first to simultaneously detect IBDV and CAV using the same RNA extraction from the bursa of Fabricius in a single and straightforward step. Therefore, this method is time saving, provides quantitative results for both targets without any cross-reaction, and reduces the risk of carrying-over contaminations. The qPCR assays here developed can be used in simplex and duplex formats for detection and quantification of large number of samples with reliable sensitivity and specificity. These tools are expected to improve surveillance and control of these ubiquitous viruses.

A proposed nomenclature for infectious bursal disease virus isolates

Infectious bursal disease virus (IBDV) was initially identified in the USA. For decades, these viruses were not categorized using a typing system because they were considered to be antigenically and pathogenically similar. In the 1980s, a second major serotype, serotype 2, was found in turkeys. Classification of IBDV became more complex with the discovery of antigenic variant strains called "variants" in the United States and a highly virulent strain known as "very virulent" or vvIBDV identified in Europe. To distinguish the IBDV strains identified prior to this time from the antigenic variant viruses, the term "classic viruses" was adopted. Studies over the next three decades produced a wealth of information on the antigenicity, pathogenicity and molecular structure of IBDV isolates. These data made it clear that the descriptive nomenclature used for IBDV was inadequate. For example, not all viruses identified as vvIBDV by genotyping are highly pathogenic; some have reassorted genome segments that result in lower virulence. Furthermore, variant viruses are not an antigenically homogeneous group and the term "classic virus" has been used interchangeably to describe antigenic and pathogenic types of IBDV. These and other issues make the current naming system for strains of IBDV archaic. The lack of uniform testing and standards for antigenicity and pathogenicity makes it difficult to categorize IBDV strains on a global basis. A new nomenclature that includes a genotyping system that can easily be applied worldwide is proposed and serves as a platform to begin discussions on its value to the scientific community.

Classification of infectious bursal disease virus into genogroups

Infectious bursal disease virus (IBDV) causes infectious bursal disease (IBD), an immunosuppressive disease of poultry. The current classification scheme of IBDV is confusing because it is based on antigenic types (variant and classical) as well as pathotypes. Many of the amino acid changes differentiating these various classifications are found in a hypervariable region of the capsid protein VP2 (hvVP2), the major host protective antigen. Data from this study were used to propose a new classification scheme for IBDV based solely on genogroups identified from phylogenetic analysis of the hvVP2 of strains worldwide. Seven major genogroups were identified, some of which are geographically restricted and others that have global dispersion, such as genogroup 1. Genogroup 2 viruses are predominately distributed in North America, while genogroup 3 viruses are most often identified on other continents. Additionally, we have identified a population of genogroup 3 vvIBDV isolates that have an amino acid change from alanine to threonine at position 222 while maintaining other residues conserved in this genogroup (I242, I256 and I294). A222T is an important mutation because amino acid 222 is located in the first of four surface loops of hvVP2. A similar shift from proline to threonine at 222 is believed to play a role in the significant antigenic change of the genogroup 2 IBDV strains, suggesting that antigenic drift may be occurring in genogroup 3, possibly in response to antigenic pressure from vaccination.

Development of an RT-qPCR assay for the specific detection of a distinct genetic lineage of the infectious bursal disease virus

The infectious bursal disease virus (IBDV) is a major health threat to the world's poultry industry despite intensive controls including proper biosafety practices and vaccination. IBDV (Avibirnavirus, Birnaviridae) is a non-enveloped virus with a bisegmented double-stranded RNA genome. The virus is traditionally classified into classic, variant and very virulent strains, each with different epidemiological relevance and clinical implications. Recently, a novel worldwide spread genetic lineage was described and denoted as distinct (d) IBDV. Here, we report the development and validation of a reverse transcription-quantitative polymerase chain reaction (RT-qPCR) assay for the specific detection of dIBDVs in the global poultry industry. The assay employs a TaqMan-MGB probe that hybridizes with a unique molecular signature of dIBDV. The assay successfully detected all the assessed strains belonging to the dIBDV genetic lineage, showing high specificity and absence of cross-reactivity with non-dIBDVs, IBDV-negative samples and other common avian viruses. Using serial dilutions of in vitro-transcribed RNA we obtained acceptable PCR efficiencies and determination coefficients, and relatively small intra- and inter-assay variability. The assay demonstrated a wide dynamic range between 10³ and 10⁸ RNA copies/reaction. This rapid, specific and quantitative assay is expected to improve IBDV surveillance and control worldwide and to increase our understanding of the molecular epidemiology of this economically detrimental poultry pathogen.

Advances in vaccine research against economically important viral diseases of food animals: Infectious bursal disease virus

Numerous reviews have been published on infectious bursal disease (IBD) and infectious bursal disease virus (IBDV). Many high quality vaccines are commercially available for the control of IBD that, when used correctly, provide solid protection against infection and disease caused by IBDV. Viruses are not static however; they continue to evolve and vaccines need to keep pace with them. The evolution of IBDV has resulted in very virulent strains and new antigenic types of the virus. This review will discuss some of the limitations associated with existing vaccines, potential solutions to these problems and advances in new vaccines for the control of IBD.

Infectious bursal disease virus in poultry: current status and future prospects

Infectious bursal disease virus (IBDV) affects immature B lymphocytes of the bursa of Fabricius and may cause significant immunosuppression. It continues to be a leading cause of economic losses in the poultry industry. IBDV, having a segmented double-stranded RNA genome, is prone to genetic variation. Therefore, IBDV isolates with different genotypic and phenotypic diversity exist. Understanding these features of the virus and the mechanisms of protective immunity elicited thereof is necessary for developing vaccines with improved efficacy. In this review, we highlighted the pattern of virus evolution and new developments in prophylactic strategies, mainly the development of new generation vaccines, which will continue to be of interest for research as well as field application in the future.

Genome Sequence of a Distinct Infectious Bursal Disease Virus

Infectious bursal disease virus is a relevant avian pathogen that affects poultry production. Here, we report the full-length coding sequence of the Uruguayan strain dIBDV/UY/2014/2202, isolated from a commercial broiler flock. The strain belongs to the distinct IBDV lineage that is widely distributed in South America.