Genomic sequence of an infectious bursal disease virus isolate from Zambia: classical attenuated segment B reassortment in nature with existing very virulent segment A

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.

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.

Genotyping and Molecular Characterization of Infectious Bursal Disease Virus Identified in Important Poultry-Raising Areas of China During 2019 and 2020

Infectious bursal disease (IBD) is an acute and highly contagious immunosuppressive disease caused by the infectious bursal disease virus (IBDV), which seriously threatens the healthy development of the poultry industry. Since its spread to China in the early 1990s, the very virulent IBDV (vvIBDV) characterized by high lethality, has been the focus of prevention and control. However, the novel variant IBDV (nVarIBDV), which has been widely prevalent in China since 2017, has brought a new threat to the poultry industry. In this study, the prevalence of IBDV in the important poultry-raising areas of China from 2019 to 2020 was detected. Of these, 45.1% (101/224) of the samples and 61.9% (26/42) of the chicken flocks were shown to be positive for IBDV. For 50 IBDVs, the sequences of the hypervariable region of the VP2 gene in segment A and of the B-marker of the VP1 gene in segment B were analyzed. The results revealed the coexistence of a number of different IBDV genotypes, including A2dB1 (nVar, 26/50, 52.0%), A3B3 (HLJ0504-like, 15/50, 30.0%), A1B1 (classical, 1/50, 2.0%), and A8B1 (attenuated, 1/50, 2.0%). This indicated that the newly emerging nVarIBDV of A2dB1 and the persistently circulating HLJ0504-like vvIBDV of A3B3 are the two important epidemic strains. Furthermore, we established that segment reassortment has occurred among these circulating strains. This study is the first to reveal the novel epidemic characteristics of IBDV since the report of the emerging nVarIBDV of A2dB1 in China.

Characterization and pathogenicity of a naturally reassortant and recombinant infectious bursal disease virus in China

Infectious bursal disease virus (IBDV), an Avibirnavirus, is the pathogen of infectious bursal disease, which is a severely immunosuppressive disease in 3-15-week-old chickens. Different phenotypes of IBDV, including classical, variant, very virulent (vv) and attenuated IBDV, have been reported in many chicken-rearing countries worldwide. Here, we isolated and identified a naturally reassortant and recombinant IBDV (designated GXB02) from 20-day-old chickens with clinicopathological changes of infectious bursal disease (IBD) in Guangxi Province, China. Whole genomic sequencing showed that the strain GXB02 simultaneously has both reassortant and recombinant characteristics with segments A and B being derived from recombinant intermediate vaccine strain and classic strains of IBDV. Segment A of strain GXB02 was incorporated into the skeleton of an intermediate IBDV vaccine strain (W2512), where the breakpoints of two recombinant events located at nucleotide positions 1468 and 1648 were replaced by reassortant vvIBDV (PK2) and vvIBDV (D6948) of segment A, respectively. We used this GXB02 strain to inoculate 21-day-old specific-pathogen-free chickens to evaluate its pathogenicity. Strain GXB02 has clinicopathologic characteristics of IBD with severe bursal lesions, as evidenced by necrosis, depletion of lymphocytes, and follicle atrophy, indicating that reassortment with classical strains in segment B or/and recombination with very virulent strains increased pathogenicity of the strain GXB02 in chickens. These findings provide important insights into the genetic exchange between classic and attenuated strains of IBDV with two recombinant events occurring at the intermediate derivative segment A with vvIBDV strains, thereby increasing the difficulty of prevention and control of IBD due to novel reassortant-recombinant strains.

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.

Identification and Pathogenicity Evaluation of a Novel Reassortant Infectious Bursal Disease Virus (Genotype A2dB3)

Infectious bursal disease virus (IBDV) is a non-enveloped, bi-segmented double-stranded RNA virus and the causative agent of a poultry immunosuppressive disease known as infectious bursal disease (IBD). The novel variant IBDV (nVarIBDV) recently posed a great threat to the development of the poultry industry. In this study, we identified a novel segment-reassortant IBDV strain, IBDV-JS19-14701 (Genotype A2dB3). Phylogenic analysis showed that Segments A and B of IBDV-JS19-14701 were derived from emerging nVarIBDV (Genotype A2dB1) and long-prevalent HLJ0504-like strains (Genotype A3B3) in China, respectively. The pathogenicity of IBDV-JS19-14701 was further evaluated via animal experiments. IBDV-JS19-14701 exhibited a similar virulence to chickens with the nVarIBDV. The identification of this reassortment event is beneficial for understanding the epidemiology of nVarIBDV and will contribute to the efficient prevention and control of IBD.

Discrete Virus Factories Form in the Cytoplasm of Cells Coinfected with Two Replication-Competent Tagged Reporter Birnaviruses That Subsequently Coalesce over Time

The Birnaviridae family, responsible for major economic losses to poultry and aquaculture, is composed of nonenveloped viruses with a segmented double-stranded RNA (dsRNA) genome that replicate in discrete cytoplasmic virus factories (VFs). Reassortment is common; however, the underlying mechanism remains unknown given that VFs may act as a barrier to genome mixing. In order to provide new information on VF trafficking during dsRNA virus coinfection, we rescued two recombinant infectious bursal disease viruses (IBDVs) of strain PBG98 containing either a split GFP11 or a tetracysteine (TC) tag fused to the VP1 polymerase (PBG98-VP1-GFP11 and PBG98-VP1-TC). DF-1 cells transfected with GFP1-10 prior to PBG98-VP1-GFP11 infection or stained with a biarsenical derivative of the red fluorophore resorufin (ReAsH) following PBG98-VP1-TC infection, had green or red foci in the cytoplasm, respectively, that colocalized with VP3 and dsRNA, consistent with VFs. The average number of VFs decreased from a mean of 60 to 5 per cell between 10 and 24 h postinfection (hpi) (P < 0.0001), while the average area increased from 1.24 to 45.01 μm² (P < 0.0001), and live cell imaging revealed that the VFs were highly dynamic structures that coalesced in the cytoplasm. Small VFs moved faster than large (average 0.57 μm/s at 16 hpi compared to 0.22 μm/s at 22 hpi), and VF coalescence was dependent on an intact microtubule network and actin cytoskeleton. During coinfection with PBG98-VP1-GFP11 and PBG98-VP1-TC viruses, discrete VFs initially formed from each input virus that subsequently coalesced 10 to 16 hpi, and we speculate that Birnaviridae reassortment requires VF coalescence.IMPORTANCE Reassortment is common in viruses with segmented double-stranded RNA (dsRNA) genomes. However, these viruses typically replicate within discrete cytoplasmic virus factories (VFs) that may represent a barrier to genome mixing. We generated the first replication competent tagged reporter birnaviruses, infectious bursal disease viruses (IBDVs) containing a split GFP11 or tetracysteine (TC) tag and used the viruses to track the location and movement of IBDV VFs, in order to better understand the intracellular dynamics of VFs during a coinfection. Discrete VFs initially formed from each virus that subsequently coalesced from 10 h postinfection. We hypothesize that VF coalescence is required for the reassortment of the Birnaviridae This study provides new information that adds to our understanding of dsRNA virus VF trafficking.

Identification and assessment of pathogenicity of a naturally reassorted infectious bursal disease virus from Henan, China

Infectious bursal disease virus (IBDV) is still a vital etiological agent in poultry farms. IBDV outbreaks occasionally occur due to the presence of very virulent, reassortment or variant strains. Vaccine immunization has played crucial roles in IBD control for decades. However, survival pressure of IBDV from the vaccine immunization also increases the reassortments of circulating viruses. In this study, an IBDV strain was isolated from several broiler farms in Henan Province, central part of China, and named IBDV HN strain. Based on the results of RT-PCR, sequencing and phylogenic analyses of VP1 and VP2 genes, the IBDV HN strain is a novel reassortment strain in the Henan region. Segment A of this strain appears to originate from the very virulent IBDV strain, while segment B comes from the other field reassortment strains. This may be the result of natural reassortant of virus circulating in the field. About 60% (6/10) of experimentally infected specific pathogen-free chickens died after 3 to 5 d post-infection with typical symptom and pathological lesions. The IBDV HN strain was prone to horizontal transmission, which poses a serious threat to the chicken industry. Further investigation on the prevalence, virulence, and evolution of HN strain IBDV will provide a foundation for the prevention and control of the disease in this region.

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.

Continuous circulation of an antigenically modified very virulent infectious bursal disease virus for fifteen years in Egypt

Infectious bursal disease virus (IBDV), the agent of an immunosuppressive and sometimes lethal disease in chickens, is causing recurrent outbreaks in broiler chickens in Egypt. In particular, an antigenically modified isolate of very virulent IBDV (vvIBDV) called 99323 was detected in Egypt nearly twenty years ago; this isolate was shown to be experimentally controlled by an antigenically classical live vaccine. However, acute IBD is still reported, even in vaccinated flocks, and little is known about the genetic and antigenic properties of viruses currently circulating in Egypt. In the present study, ten samples collected in Egyptian broiler farms in 2015 as well as five samples collected in 2001 were analyzed. Genetic analyses of partial VP2 sequences revealed that 8 isolates clustered with vvIBDV strains, and 5 with tissue culture adapted and vaccine strains. Similar results were observed for partial VP1 sequences with the exception of isolate 160019, for which VP2 clustered with the vaccine strain Bursine while VP1 clustered with vvIBDV, suggesting reassortment. For isolates genetically related to vvIBDV, antigenic profiling revealed two patterns: while some isolates exhibited typical European vvIBDV reactivity with lack of binding of mAbs 5, other revealed extensive antigenic modifications, with lack of binding of mAbs 3, 5, 6, 8 and 9, similar to isolate 99323. These different patterns were associated with a single amino acid mutation at position 321 of VP2 that is located within peak P_HI. Full genome sequencing was performed for three isolates, among which two were representative of the two antigenic patterns observed for vvIBDV as well as the reassortant isolate 160019. This study highlights the co-circulation of both antigenically typical and modified vvIBDV during the last fifteen years in Egypt.

New introduction of a very virulent infectious bursal disease virus in New York, USA

Bursa tissue samples from a pullet flock in New York State that was experiencing immune suppression related disease were sent to our laboratory in 2018. A very virulent infectious bursal disease virus (vvIBDV) was identified in those samples through molecular and pathogenicity studies and designated 1/chicken/USA/1054NY/18. Phylogenetic analyses of the hypervariable VP2 nucleotide sequence region indicated that this strain belonged to genogroup 3 which comprises the vvIBDV. Partial sequence data of the VP1 gene indicated this virus also had a VP1 typical of vvIBDV. While vvIBDV have previously been identified in the United States in California and Washington State, the 1054NY vvIBDV was most closely related to isolates from Ethiopia, suggesting it is a new introduction into the U.S. The 1054NY vvIBDV was used to challenge four-week old specific-pathogen-free (SPF) layer chicks where it caused 100% morbidity and 68.7% mortality within 4 days. Upon necropsy, gross pathological findings in infected SPF birds included small yellowish coloured bursas, some with haemorrhages on the serosal and mucosal surfaces. Microscopic lesions included inflammation, severe lymphocyte necrosis, atrophy of the follicles and follicular depletion of lymphocytes. RESEARCH HIGHLIGHTS A very virulent infectious bursal disease virus (vvIBDV) was detected in a pullet flock in New York state, USA. Nucleotide sequence analysis of the vvIBDV VP2 gene indicates it is not related to previous US vvIBDV isolates and appears to be a new introduction into the US. The New York vvIBDV caused 100% morbidity and 68.7% mortality in four-week-old specific-pathogen-free chicks.

Identification and assessment of virulence of a natural reassortant of infectious bursal disease virus

Infectious bursal disease virus (IBDV) is one of the most important immunosuppressive viral agents in poultry production. Prophylactic vaccinations of chicken flocks are the primary tool for disease control. Widely used immunoprophylaxis can, however, provide high pressure which contributes to the genetic diversification of circulating viruses, e.g. through reassortment of genome segments. We report the genetic and phenotypic characterization of a field reassortant IBDV (designated as Bpop/03) that acquired segment A from very virulent IBDV and segment B from classical attenuated D78-like IBDV. Despite the mosaic genetic make-up, the virus caused high mortality (80%) in experimentally infected SPF chickens and induced lesions typical of the acute form of IBD. The in vivo study results are in contrast with the foregoing experimental investigations in which the natural reassortants exhibited an intermediate pathotype, and underline the complex nature of IBDV virulence.

Genome sequence analysis of a distinctive Italian infectious bursal disease virus

In a recent study, an emerging infectious bursal disease virus (IBDV) genotype (ITA) was detected in IBDV-live vaccinated broilers without clinical signs of infectious bursal disease (IBD). VP2 sequence analysis showed that strains of the ITA genotype clustered separately from vaccine strains and from other IBDV reference strains, either classic or very virulent. In order to obtain a more exhaustive molecular characterization of the IBDV ITA genotype and speculate on its origin, genome sequencing of the field isolate IBDV/Italy/1829/2011, previously assigned to the ITA genotype, was performed, and the sequences obtained were compared to the currently available corresponding sequences. In addition, phylogenetic and recombination analyses were performed. Interestingly, multiple amino acid (AA) sequence alignments revealed that the IBDV/Italy/1829/2011 strain shared several AA residues with very virulent IBDV strains as well as some virulence markers, especially in the VP1 protein. Nevertheless, sequence analysis demonstrated the presence of several residues typical of IBDV strains at a low degree of virulence in the IBDV/Italy/1829/2011 strain. Although homologous recombination and reassortant phenomena may occur naturally among different IBDV strains, no evidence of those events was found in the genome of the IBDV/Italy/1829/2011 strain, which was confirmed to be a genetically distinctive IBDV genotype.

Characterization of field infectious bursal disease viruses in Zambia: evidence of co-circulation of multiple genotypes with predominance of very virulent strains

Infectious bursal disease (IBD) is a highly contagious, immunosuppressive disease of chickens and causes substantial economic losses to the poultry industry globally. This study investigated the genetic characteristics and pathological lesions induced by IBD viruses (IBDVs) that were associated with 60 suspected outbreaks in chickens during 2015-2016 in Lusaka Province, Zambia. Nucleotide sequences of VP2 hypervariable region (VP2-HVR) (n = 38) and part of VP1 (n = 37) of Zambian IBDVs were phylogenetically analysed. Phylogenetic analysis of the VP2-HVR and VP1 revealed that most viruses (n = 31 of each genome segment) clustered with the very virulent (vv) strains. The rest of the viruses clustered with the classical strains, with two of the viruses being closely related to attenuated vaccine isolates. Two of the viruses that belonged to the vv genotype had a unique amino acid (aa) substitution Q324L whereas one virus had two unique changes, N280S and E300A in the VP2-HVR aa sequence. Although Zambian strains with a vv genotype possessed virulence marker aa within VP1 at 145T, 146D and 147N, two viruses showed unique substitutions, with one virus having 147T while the other had 147H. Pathologically, it was noted that only viruses with a vv genotype appeared to be associated with inducing pathological lesions in non-lymphoid organs (proventriculus and gizzard). Whilst documenting for the first time the presence of classical virulent IBDVs, this study demonstrates the involvement of multiple genotypes, with predominance of vvIBDVs in the epidemiology of IBD in Zambia.

Differential gene expression in chicken primary B cells infected ex vivo with attenuated and very virulent strains of infectious bursal disease virus (IBDV)

Infectious bursal disease virus (IBDV) belongs to the family Birnaviridae and is economically important to the poultry industry worldwide. IBDV infects B cells in the bursa of Fabricius (BF), causing immunosuppression and morbidity in young chickens. In addition to strains that cause classical Gumboro disease, the so-called 'very virulent' (vv) strain, also in circulation, causes more severe disease and increased mortality. IBDV has traditionally been controlled through the use of live attenuated vaccines, with attenuation resulting from serial passage in non-lymphoid cells. However, the factors that contribute to the vv or attenuated phenotypes are poorly understood. In order to address this, we aimed to investigate host cell-IBDV interactions using a recently described chicken primary B-cell model, where chicken B cells are harvested from the BF and cultured ex vivo in the presence of chicken CD40L. We demonstrated that these cells could support the replication of IBDV when infected ex vivo in the laboratory. Furthermore, we evaluated the gene expression profiles of B cells infected with an attenuated strain (D78) and a very virulent strain (UK661) by microarray. We found that key genes involved in B-cell activation and signalling (TNFSF13B, CD72 and GRAP) were down-regulated following infection relative to mock, which we speculate could contribute to IBDV-mediated immunosuppression. Moreover, cells responded to infection by expressing antiviral type I IFNs and IFN-stimulated genes, but the induction was far less pronounced upon infection with UK661, which we speculate could contribute to its virulence.

Role of naturally occurring genome segment reassortment in the pathogenicity of IBDV field isolates in Three-Yellow chickens

Reassortment among genome segments of infectious bursal disease virus (IBDV) field isolates was reported frequently worldwide, however the pathogenicity of the reassortant field IBDV is poorly understood. In this paper, a pathogenicity study on four representative IBDV field strains isolated from Southern China between 2005 and 2011 was conducted. Twenty-eight-day-old Three-Yellow chickens were divided into four groups and were inoculated intraocularly with one of the four field IBDV strains, namely NN1172, NN1005, GD10111 and JS7, respectively. The mortality and relative weight of bursa and thymus were subsequently determined in the acute phase of infection. In addition, B cells, T cells (CD4(+) and CD8(+)) and virus were quantified in the bursa of Fabricius and thymus, respectively, by flow cytometry and real-time reverse transcription-polymerase chain reaction. The results showed that isolate NN1172, of which parts of segment A and B encoding the hypervariable (v) region of viral protein (VP2) and VP1, respectively, derived from vvIBDV strains, showed the most severe pathogenicity, and caused the most severe bursal B cell depletion as well as CD4(+) and CD8(+) T cell infiltration in the bursa of Fabricius. However, the virus induced the strongest decrease in CD4(+) and CD8(+) T cells in the thymus and exhibited the most efficient viral replication in the target organs. Isolate NN1005, whose vVP2 derived from vvIBDV and VP1 from unidentified origin, exhibited relatively lower pathogenicity compared to NN1172. The other two isolates, JS7 and GD10111, of which the vVP2 derived from vvIBDV and intermediate IBDV, and VP1 from 002-73 and attenuated IBDV, respectively, showed the lowest level of virulence. Our results suggest that various IBDV field isolates with different natural segment reassortments exhibit differential pathogenicity after infection of commercial Three-Yellow chickens.

Molecular characterization of field infectious bursal disease virus isolates from Nigeria

Aim:

To characterize field isolates of infectious bursal disease virus (IBDV) from outbreaks in nine states in Nigeria through reverse transcription polymerase chain reaction (RT-PCR) and sequence analysis of portions of the VP2 and VP1 genes and to determine the presence or absence of reassortant viruses.

Materials and Methods:

A total of 377 bursa samples were collected from 201 suspected IBD outbreaks during 2009 to 2014 from nine states in Nigeria. Samples were subjected to RT-PCR using VP2 and VP1 gene specific primers, and the resulting PCR products were sequenced.

Results:

A total of 143 samples were positive for IBDV by RT-PCR. These assays amplified a 743 bp fragment from nt 701 to 1444 in the IBDV VP2 hypervariable region (hvVP2) of segment A and a 722 bp fragment from nt 168 to 889 in the VP1 gene of segment B. RT-PCR products were sequenced, aligned and compared with reference IBDV sequences obtained from GenBank. All but one hvVP2 sequence showed similarity to very virulent IBDV (vvIBDV) reference strains, yet only 3 of the VP1 67 VP1 sequences showed similarity to the VP1 gene of vvIBDV. Phylogenetic analysis revealed a new lineage of Nigerian reassortant IBDV strains.

Conclusion:

Phylogenetic analysis of partial sequences of genome segment A and B of IBDV in Nigeria confirmed the existence of vvIBDV in Nigeria. In addition, we noted the existence of reassortant IBDV strains with novel triplet amino acid motifs at positions 145, 146 and 147 in the reassorted Nigerian IBDV.

In vitro reassortment between Infectious Pancreatic Necrosis Virus (IPNV) strains: The mechanisms involved and its effect on virulence

Reassortment is one of the main mechanisms of evolution in dsRNA viruses with segmented genomes. It contributes to generate genetic diversity and plays an important role in the emergence and spread of new strains with altered virulence. Natural reassorment has been demonstrated among infectious pancreatic necrosis-like viruses (genus Aquabirnavirus, Birnaviridae). In the present study, coinfections between different viral strains, and genome sequencing by the Sanger and Illumina methods were applied to analyze the frequency of reassortment of this virus in vitro, the possible mechanisms involved, and its effect on virulence. Results have demonstrated that reassortment is a cell-dependent and non-random process, probably through differential expression of the different mRNA classes in the ribosomes of a specific cell, and by specific associations between the components to construct the ribonucleoprotein (RNP) complexes and/or RNP cross-inhibition. However, the precise mechanisms involved, known in other viruses, still remain to be demonstrated in birnaviruses.

Identification of a European interserotypic reassortant strain of infectious bursal disease virus

Infectious bursal disease virus (IBDV, family Birnaviridae) is a bi-segmented double-stranded RNA virus for which two serotypes are described. Serotype 1 replicates in the bursa of Fabricius and causes an immunosuppressive and potentially fatal disease in young chickens. Serotype 2 is apathogenic in poultry species. Up to now, only one natural event of interserotypic reassortment has been described after the introduction of very virulent IBDV (vvIBDV) in the USA in 2009, resulting in an IBDV strain with its segment A related to vvIBDV and its segment B related to US serotype 2 strain OH. Here, we present the first European isolate illustrative of interserotypic reassortment. The reassorting isolate, named 100056, exhibits a genomic segment A typical of current European vvIBDV but a segment B close to European serotype 2 viruses, supporting an origin distinct from US strains. When inoculated into SPF chickens, isolate 100056 induced mild clinical signs in the absence of mortality but caused a severe bursal atrophy, which strongly suggests an immunosuppressive potential. These results illustrate that interserotypic reassortment is another mechanism that can create IBDV strains with a modified acute pathogenicity. As a consequence, and for a more precise inference of the possible phenotype, care should be taken that the molecular identification of IBDV strains is targeted to both genome segments.

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.

Evaluation of a Phylogenetic Marker Based on Genomic Segment B of Infectious Bursal Disease Virus: Facilitating a Feasible Incorporation of this Segment to the Molecular Epidemiology Studies for this Viral Agent

Background

Infectious bursal disease (IBD) is a highly contagious and acute viral disease, which has caused high mortality rates in birds and considerable economic losses in different parts of the world for more than two decades and it still represents a considerable threat to poultry. The current study was designed to rigorously measure the reliability of a phylogenetic marker included into segment B. This marker can facilitate molecular epidemiology studies, incorporating this segment of the viral genome, to better explain the links between emergence, spreading and maintenance of the very virulent IBD virus (vvIBDV) strains worldwide.

Methodology/Principal Findings

Sequences of the segment B gene from IBDV strains isolated from diverse geographic locations were obtained from the GenBank Database; Cuban sequences were obtained in the current work. A phylogenetic marker named B-marker was assessed by different phylogenetic principles such as saturation of substitution, phylogenetic noise and high consistency. This last parameter is based on the ability of B-marker to reconstruct the same topology as the complete segment B of the viral genome. From the results obtained from B-marker, demographic history for both main lineages of IBDV regarding segment B was performed by Bayesian skyline plot analysis. Phylogenetic analysis for both segments of IBDV genome was also performed, revealing the presence of a natural reassortant strain with segment A from vvIBDV strains and segment B from non-vvIBDV strains within Cuban IBDV population.

Conclusions/Significance

This study contributes to a better understanding of the emergence of vvIBDV strains, describing molecular epidemiology of IBDV using the state-of-the-art methodology concerning phylogenetic reconstruction. This study also revealed the presence of a novel natural reassorted strain as possible manifest of change in the genetic structure and stability of the vvIBDV strains. Therefore, it highlights the need to obtain information about both genome segments of IBDV for molecular epidemiology studies.

Naturally occurring reassortant infectious bursal disease virus in northern China

Infectious bursal disease virus (IBDV) is a bi-segmented, double-stranded RNA virus that belongs to the genus Avibirnavirus of the family of Birnavirideae. The co-evolution of genome segments is a major evolutionary feature for IBDV. However, in recent years, some strains exhibited markedly different genetic relationships for segments A and B. In this study, we firstly isolated a new type of reassortment IBDV strain named IBD13HeB01 from northern China. The full-length genomes of segments A and B were cloned and identified. Sequence analysis revealed that IBD13HeB01 was a segment-reassortment strain, whose segment A was derived from very virulent strain and segment B from attenuated IBDV. In addition, the virulence of IBD13HeB01 strain was evaluated using SPF chickens. This study is not only beneficial for further understanding of the viral evolution but also suggests the potential risk of application of the live vaccines of IBDV.