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.

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.

Detection and characterization of a novel marine birnavirus isolated from Asian seabass in Singapore.

BACKGROUND: Lates calcarifer, known as seabass in Asia and barramundi in Australia, is a widely farmed species internationally and in Southeast Asia and any disease outbreak will have a great economic impact on the aquaculture industry. Through disease investigation of Asian seabass from a coastal fish farm in 2015 in Singapore, a novel birnavirus named Lates calcarifer Birnavirus (LCBV) was detected and we sought to isolate and characterize the virus through molecular and biochemical methods. METHODS: In order to propagate the novel birnavirus LCBV, the virus was inoculated into the Bluegill Fry (BF-2) cell line and similar clinical signs of disease were reproduced in an experimental fish challenge study using the virus isolate. Virus morphology was visualized using transmission electron microscopy (TEM). Biochemical analysis using chloroform and 5-Bromo-2'-deoxyuridine (BUDR) sensitivity assays were employed to characterize the virus. Next-Generation Sequencing (NGS) was also used to obtain the virus genome for genetic and phylogenetic analyses. RESULTS: The LCBV-infected BF-2 cell line showed cytopathic effects such as rounding and granulation of cells, localized cell death and detachment of cells observed at 3 to 5 days' post-infection. The propagated virus, when injected intra-peritoneally into naïve Asian seabass under experimental conditions, induced lesions similar to fish naturally infected with LCBV. Morphology of LCBV, visualized under TEM, revealed icosahedral particles around 50 nm in diameter. Chloroform and BUDR sensitivity assays confirmed the virus to be a non-enveloped RNA virus. Further genome analysis using NGS identified the virus to be a birnavirus with two genome segments. Phylogenetic analyses revealed that LCBV is more closely related to the Blosnavirus genus than to the Aquabirnavirus genus within the Birnaviridae family. CONCLUSIONS: These findings revealed the presence of a novel birnavirus that could be linked to the disease observed in the Asian seabass from the coastal fish farms in Singapore. This calls for more studies on disease transmission and enhanced surveillance programs to be carried out to understand pathogenicity and epidemiology of this novel virus. The gene sequences data obtained from the study can also pave way to the development of PCR-based diagnostic test methods that will enable quick and specific identification of the virus in future disease investigations.

Molecular characterization and phylogenetic analysis of very virulent infectious bursal disease virus circulating in Morocco during 2016-2017.

Very virulent infectious bursal disease virus (vvIBDV), the cause of significant economic losses in many poultry-producing areas, has been present in Morocco since 1991. In spite of the introduction of vaccination, disease outbreaks are frequently observed. To ascertain if vaccines failure may be due to the emergence of new strains, the aim of this study was to perform for the first time the molecular characterization of vvIBDV strains circulating in Morocco by focusing on the hypervariable region (HVR) of the VP2 protein, which is frequently used for molecular epidemiology and phylogenetic studies. Field samples of haemorrhagic bursae of Fabricius were collected for molecular characterization in different parts of the country during 2016-2017 from 48 chicken flocks showing symptoms of disease. In a phylogenetic tree, nucleotide sequences containing the VP2 HVR of 13 samples that were positive for vvIBDV formed a common branch with those of vvIBDV references strains published in GenBank, but they clearly grouped into a distinct subcluster. An alignment of the deduced amino acid sequences, in addition to confirming the presence of the "signature" typical of the vvIBDV HVR, also revealed the presence of substitutions in hydrophilic loops that are known to be involved in the elicitation of neutralizing antibodies. One of these substitutions is unique to the Moroccan isolates. These results represent the first molecular characterization of vvIBDV isolates in Morocco and may indicate that one of the causes of vaccine ineffectiveness is antigenic drift.

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.

Detection of different genotypes of infectious bronchitis virus and of infectious bursal disease virus in European broilers during an epidemiological study in 2013 and the consequences for the diagnostic approach.

To gather recent data regarding the infectious bronchitis (IB) and infectious bursal disease (IBD) situation in Europe, a large-scale field epidemiological survey using diagnostic samples has been implemented in 2013 for about six months in several European countries: France, Germany, Greece, Italy, the Netherlands, Poland, Portugal, the Republic of Ireland, Spain and the UK. In 234 flocks that were sampled, strains from 10 different IBV genotypes were detected: the 793B genotype was detected most frequently, followed by QX, Massachusetts (Mass) and the Xindadi-like strains. Strains belonging to the Q1, Ark, D274, D1466, Italy-02 and B1648 genotypes were detected as well, although less frequently. The separate sampling of tracheas and kidneys for IBV detection using reverse transcriptase PCR was very useful, as different genotypes or significant differences in sequences of the same genotype were detected between both organs. The data of this survey also provided valuable information about the replication of IBD vaccines and subsequent infectious bursal disease virus (IBDV) antibody responses under field conditions. The detection of five non-vvIBDV field strains of two different genotypes shows the presence of non-vvIBDV non-vaccine strains, which can easily be undetected in Europe due to the focus on sampling of clinically ill birds. Detection of vaccine virus in the bursa and antibody response to the IBD vaccination in flocks that had been vaccinated by the drinking water with a live attenuated vaccine compared to a vaccination in the hatchery using an immune-complex vaccine showed a delayed replication of the vaccines that had been applied by the drinking water, indicating mistakes in the timing and/or application of the vaccines.

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.

Molecular characterization of very virulent infectious bursal disease virus strains circulating in Egypt from 2003 to 2014.

In the present study, four very virulent infectious bursal disease virus (vvIBDV) isolates from flocks of chickens with vaccination failure in Egypt in 2003, 2007, 2010 and 2014 were characterized. The four viruses, designated USC2003, USC2007, USC2010 and USC2014, were detected by reverse transcription PCR, subjected to sequencing of both genomic segments (A and B) and compared with geographically and phylogenetically diverse IBDV strains. Phylogenetic analysis of segment A (complete) and B (partial) revealed a close relationship between Egyptian and vvIBDV reference strains of European and Asian origin. The sequences of segments of A and B the current Egyptian isolates were 96.1-98.2% and 96.5-98.7% identical, respectively, to those of other known vvIBDV isolates. The deduced amino acid sequences of VP1, polyprotein (pVP2-VP4-VP3) and VP5 revealed the presence of putative virulence determinants of Egyptian isolates compared with vvIBDV and less virulent (classical and variant) strains. The Egyptian isolates also possess unique amino acids substitutions within the hypervariable region of VP2 that differ from those of other reference IBDV strains. Further studies may be necessary to determine the pathogenic significance of these amino acid substitutions to fully understand the molecular epidemiology and evolution of IBDV.

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.

Isolation of novel variants of infectious bursal disease virus from different outbreaks in Northeast India.

Infectious bursal disease virus (IBDV) is a highly infectious disease of young chicken that predominantly affects the immune system. In the present study, we are reporting first comprehensive study of IBDV outbreaks from the Northeastern part of India. Northeast India shares a porous border with four different countries; and as a rule any outbreak in the neighboring countries substantially affects the poultry population in the adjoining states. Nucleotide sequence analysis of the VP2 gene of the IBDV isolates from the Northeastern part of India suggested the extreme virulent nature of the virus. The virulent marker amino acids (A222, I242, Q253, I256 and S299) in the hypervariable region of the Northeastern isolates were found identical with the reported very virulent strains of IBDV. A unique insertion of I/L294V was recorded in all the isolates of the Northeastern India. The study will be useful in understanding the circulating pathotypes of IBDV in India.

Molecular characterization of infectious bursal disease viruses detected in vaccinated commercial broiler flocks in Lusaka, Zambia.

Infectious bursal disease (IBD) is an acute, highly contagious, and immunosuppressive viral disease of young chickens and remains one of the economically most important diseases threatening the poultry industry worldwide. In this study, 16 and 11 nucleotide sequences of the VP2 hypervariable region (VP2-HVR) and part of VP1, respectively, of IBD virus (IBDV) detected in vaccinated broiler chickens in Lusaka in 2012 were determined. Phylogenetic analysis revealed that these Zambian IBDVs separated into three genotypes of very virulent (VV) IBDVs. Although the majority of these viruses belonged to the African VV type (VV1), which consisted of viruses from West Africa, South Africa and Zambia, one virus belonged to the East African VV type (VV2). Interestingly, a Zambian IBDV belonging to the VV3 genotype (composed of viruses from several continents) clustered with attenuated vaccine strains. Although sequence analysis of VP2-HVR showed that all detected Zambian IBDVs had conserved putative virulence marker amino acids (i.e., 222A, 242I, 256I, 294I and 299S), one virus had two unique amino acid substitutions, N280S and E300A. This study demonstrates the diversity of Zambian IBDVs and documents for the first time the possible involvement of attenuated vaccine strains in the epidemiology of IBD in Zambia. Strict biosecurity of poultry farms, monitoring of live vaccine use in the field, surveillance and characterization of IBDV in poultry and development of a vaccine from local or regional IBDV field strains are recommended for improved IBD control in Zambia.

Molecular characterization of infectious bursal disease viruses from Pakistan.

Since the first report of infectious bursal disease in Pakistan in 1987, outbreaks have been common even in vaccinated flocks. Despite appropriate administration of vaccines, concerns arise if the circulating strains are different from the ones used in the vaccine. Here, we sequenced the hypervariable region (HVR) of the VP2 gene of circulating strains of infectious bursal disease virus (IBDV) originating from outbreaks (n = 4) in broiler flocks in Pakistan. Nucleotide sequencing followed by phylogeny and deduced amino acid sequence analysis showed the circulating strains to be very virulent (vv) and identified characteristic residues at position 222 (A), 242 (I), 256 (I), 294 (I) and 299 (S). In addition, a substitution at positions 221 (Q→H) was found to be exclusive to Pakistani strains in our analysis, although a larger dataset is required to confirm this finding. Compared to vaccine strains that are commonly used in Pakistan, substitution mutations were found at key amino acid positions in VP2 that may be responsible for potential changes in neutralization epitopes and vaccine failure.

A molecular epidemiology study based on VP2 gene sequences reveals that a new genotype of infectious bursal disease virus is dominantly prevalent in Italy.

A distinctive infectious bursal disease (IBD) virus genotype (ITA) was detected in IBD-live vaccinated broilers in Italy without clinical signs of IBD. It was isolated in specific-pathogen-free eggs and molecularly characterized in the hypervariable region of the virus protein (VP) 2. Phylogenetic analysis showed that ITA strains clustered separately from other homologous reference sequences of IBDVs, either classical or very virulent, retrieved from GenBank or previously reported in Italy, and from vaccine strains. The new genotype shows peculiar molecular characteristics in key positions of the VP2 hypervariable region, which affect charged or potentially glycosylated amino acids virtually associated with important changes in virus properties. Characterization of 41 IBDV strains detected in Italy between 2013 and 2014 showed that ITA is emergent in densely populated poultry areas of Italy, being 68% of the IBDV detections made during routine diagnostic activity over a two-year period, in spite of the immunity induced by large-scale vaccination. Four very virulent strains (DV86) and one classical strain (HPR2), together with eight vaccine strains, were also detected. The currently available epidemiological and clinical data do not allow the degree of pathogenicity of the ITA genotype to be defined. Only in vivo experimental pathogenicity studies conducted in secure isolation conditions, through the evaluation of clinical signs and macro/microscopic lesions, will clarify conclusively the virulence of the new Italian genotype.

Genotypic characterization of Indian isolates of infectious bursal disease virus strains by reverse transcription-polymerase chain reaction combined with restriction fragment length polymorphism analysis.

The reverse transcription PCR (RT-PCR) combined with restriction fragment length polymorphism (RFLP) is used for the differentiation of classical virulent (cv), virulent (v) and very virulent (vv) strains of infectious bursal disease virus (IBDV) isolates from chicken bursal tissues in southern states of India. In the present study, six different isolates (MB11, HY12, PY12, BGE14, VCN14 and NKL14) of IBDV strains were subjected for genotyping along with vaccine virus (Georgia, intermediate strain) using RT-PCR for amplification of a 743 bp sequence in the hypervariable region of VP2 gene followed by restriction enzyme digestion with 5 different restriction enzymes (BspMI, SacI, HhaI, StuI and SspI). The RT-PCR products obtained from vvIBDV strains were digested by SspI enzyme except PY12, BGE14 and MB11 isolates. The SacI digested the isolate MB11, PY12 and the vaccine strain, but it did not cleave the very virulent isolates of IBDV. HhaI cleaved all the isolates with different restriction profile patterns. StuI digested all the vvIBDV isolates and BspMI was not able to differentiate field isolates from vaccine strain. Though RT-PCR combined with RFLP is a genotypic method, further confirmation of serotypes to distinguish the vvIBDV from cvIBDV has to be carried out using pathogenicity studies.

[Naturally occurring reassortants of infectious bursal disease virus - A review].

Infectious bursal disease virus (IBDV) is an important representative of Birnaviridae, which causes infectious bursal disease (IBD), one important immuno-suppressive and fatal disease threatening the poultry husbandry. The naturally occurring reassortants of IBDV induced new risks to disease prevention and control. Here, we reviewed the main types of the genome segments reassortants and intragenic recombination, the inherent mechanism and the biological significances were analyzed, which would give us new insights into the virus genetic evolution research and the disease control strategy.

Molecular characterization of infectious bursal disease virus (IBDV) isolated in Argentina indicates a regional lineage.

In Argentina, classical vaccines are used to control infectious bursal disease virus (IBDV); however, outbreaks of IBDV are frequently observed. This could be due to failures in the vaccination programs or to the emergence of new strains, which would be able to break through the protection given by vaccines. Hence, genetic characterization of the viruses responsible for the outbreaks that occurred in recent years is crucial for the evaluation of the control programs and the understanding of the epidemiology and evolution of IBDV. In this study, we characterized 51 field samples collected in Argentina (previously identified as IBDV positive) through the analysis of previously identified apomorphic sequences. Phylogenetic analysis of regVP2 showed that 42 samples formed a unique cluster (Argentinean lineage), seven samples were typical classical strains (one of them was a vaccine strain), and two belonged to the very virulent lineage (vvIBDV). Interestingly, when the analysis was performed on the regVP1 sequences, the field samples segregated similarly to regVP2; thus, we observed no evidence of a reassortment event in the Argentinean samples. Amino acid sequence analysis of regVP2 showed a particular pattern of residues in the Argentinean lineage, particularly the presence of T272, P289 and F296, which had not been reported before as signature sequences for any IBDV phenotype. Notably, the residue S254, characteristic of the antigenic variant, was not present in any of the Argentinean samples.

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

Infectious bursal disease virus (IBDV) is one of the most concerning health problems for world poultry production. IBDVs comprise four well-defined evolutionary lineages known as classic (c), classic attenuated (ca), variant (va) and very virulent (vv) strains. Here, we characterized IBDVs from South America by the genetic analysis of both segments of the viral genome. Viruses belonging to c, ca and vv strains were unambiguously classified by the presence of molecular markers and phylogenetic analysis of the hypervariable region of the vp2 gene. Notably, the majority of the characterized viruses (9 out of 15) could not be accurately assigned to any of the previously described strains and were then denoted as distinct (d) IBDVs. These dIBDVs constitute an independent evolutionary lineage that also comprises field IBDVs from America, Europe and Asia. The hypervariable VP2 sequence of dIBDVs has a unique and conserved molecular signature (272T, 289P, 290I and 296F) that is a diagnostic character for classification. A discriminant analysis of principal components (DAPC) also identified the dIBDVs as a cluster of genetically related viruses separated from the typical strains. DAPC and genetic distance estimation indicated that the dIBDVs are one of the most genetically divergent IBDV lineages. The vp1 gene of the dIBDVs has non-vvIBDV markers and unique nucleotide and amino acid features that support their divergence in both genomic segments. The present study suggests that the dIBDVs comprise a neglected, highly divergent lineage that has been circulating in world poultry production since the early time of IBDV emergence.

Persistence and Tissue Distribution of Infectious Bursal Disease Virus Serotypes 1 and 2 in Turkeys.

Two experiments were conducted to determine the persistence and tissue distribution of serotypes 1 and 2 of infectious bursal disease virus (IBDV) in specific-pathogen-free and vaccinated turkeys. In Experiment 1, three groups of 2-wk-old turkey poults, including a negative control group, were used. In groups 1 and 2, 13 poults in each group were challenged with either serotype 1 (STC) or serotype 2 (OH) strains using an inoculum of 10(4) 50% embryo infectious dose (EID50)/0.2 ml/bird. Thymus, bursa, spleen, kidney, lungs, liver, pancreas, caecum, and breast and thigh muscles were sampled at predetermined intervals. The bursal tissues from birds inoculated with either serotype were reverse transcriptase-PCR (RT-PCR) positive up to 21 days postinoculation (DPI). In both groups virus isolation from bursas was possible up to 14 DPI. Except for the bursas and spleens in birds inoculated with serotype 1 and bursas in birds inoculated with serotype 2, all other tissues were RT-PCR negative. In Experiment 2, five groups of turkey poults were used. At 4 wk of age, group 1 was challenged with a serotype 1 STC strain and group 2 with serotype 2 OH strain using an inoculum size of 10(2) EID50/0.2 ml for both serotypes. Groups 3 and 4 were vaccinated at 2 wk of age using an inactivated serotype 1 IBDV vaccine. At 2 wk postvaccination, groups 3 and 4 were challenged with STC and OH strains respectively. From group 1, bursal, spleen, and liver tissues were RT-PCR positive up to 14 DPI; breast muscle and kidney tissues were positive up to 7 DPI; and lungs and pancreatic tissues were positive up to 3 DPI. From group 2, bursal tissues were RT-PCR positive up to 14 DPI and lung tissues up to 3 DPI. All of the tissue samples collected from groups 3, 4, and 5 were RT-PCR negative. Virus could not be isolated from RT-PCR positive bursal homogenate. In this work, it was confirmed that the virus persisted in the bursa longer than in any other tissues. The difference in the results between Experiments 1 and 2 could be due to the age of poults at vaccination and the higher inoculum size used in Experiment 1. This study indicates that turkeys are more resistant to IBDV as compared to chickens. Viruses of serotypes 1 and 2 infect turkeys and persist in bursal tissue for 14 days and RNA was detected up to 21 days.

Efficacy, Safety, and Interactions of a Live Infectious Bursal Disease Virus Vaccine for Chickens Based on Strain IBD V877.

Infectious bursal disease (IBD) is a highly contagious disease in young chickens which can result in high morbidity and mortality and also in great economic losses. The main target for the virus is the lymphoid tissue with a special predilection for the bursa of Fabricius. Several vaccines are available to control the disease. Intermediate plus vaccines are used in chickens with high maternal antibody titers which face high infection pressure. An example of an intermediate plus vaccine is a live vaccine based on IBD strain V877. The results of an efficacy study in commercial broilers with different levels of maternally derived antibodies (MDA) showed that the V877-based IBD vaccine can break through maternal antibody titers of higher than 1100 as determined by an IBD ELISA. The safety of the vaccine was demonstrated in a study in which specific-pathogen-free (SPF) chickens were vaccinated with a tenfold dose of the vaccine strain and a tenfold dose of the vaccine strain after five back passages in SPF chickens. The vaccine virus caused lesions, as could be expected for an intermediate plus vaccine, but the scores were not much higher than the maximal scores allowed for mild IBD vaccines in the European Pharmacopoeia, and reversion to virulence was absent. In studies in SPF chickens, there were no negative impacts by the IBD V877 vaccine on the efficacy of a live QX-like IB vaccine and a live Newcastle disease La Sota vaccine in vaccination challenge studies, although the IBD vaccine had a negative effect on the antibody response generated by the QX-like IB vaccine. It is concluded that the IBD V877 vaccine has the capacity to break through high levels of MDA, has a satisfactory safety profile, and interactions with other live vaccines are limited. In order to limit bursal lesions after vaccination it is recommended to confirm the presence of MDA before vaccinating with the V877 vaccine.

Molecular epidemiology studies on partial sequences of both genome segments reveal that reassortant infectious bursal disease viruses were dominantly prevalent in southern China during 2000-2012.

A molecular epidemiology study of infectious bursal disease viruses (IBDVs) isolated from seven provinces in southern China during the years 2000-2012 was performed based on partial sequences of genome segments A and B, namely the hypervariable region of the A-VP2 gene (A-vVP2) and the b fragment of VP1 gene (B-VP1b) from a total of 91 field isolates. Sequence analysis based on vVP2 revealed that 72 out of 91 isolates had the same characteristic amino acid (aa) sequences as vvIBDV. The mutation of D212N in A-vVP2 has become prevalent in the recent isolates. The origin of the field isolates with vvIBDV characteristic amino acid residues was complex, evidenced by the findings that more than one subgroup of strains prevailed in each province. When B-VP1b was analyzed, there were three lineages among the field isolates, and none of the isolates had a relationship to vvIBDV-related segment B. Phylogenetic analysis of both segments revealed that only a few isolates (13/91) had the same genetic relatives in consensus trees based on segments A and B, whereas the majority of the isolates (85.71%, 78/91) were identified to be naturally reassorted strains. Based on the origin of each segment, at least six types of reassortant IBDVs prevailed in southern China, three of which were shown to be dominant: segment A from vvIBDV and B from attenuated IBDV, segment A of vvIBDV and B from 002-73-like IBDV, and segment A of vvIBDV and B from HLJ0504 or a similar strain. Our findings suggest that both genomic segments of field IBDVs has been evolving, and continuous monitoring of the evolution of field IBDV genome is therefore urgently needed in the control of IBDV.