Molecular characterisation of very virulent infectious bursal disease viruses in Taiwan

Molecular characterisation of infectious bursal disease virus (IBDV) isolated from commercial broiler chickens in Nile Delta

Infectious bursal disease virus (IBDV) is a highly infectious disease affecting young chickens that alters predominantly the immune system. Emergence of new variants causes severe economic losses not only in Egypt but also all over the world. For this purpose assessment of infectious bursal disease virus (IBDV) genotypes in 20 commercial broiler flocks aged 20–35 days raised in 5 provinces in the Nile Delta, Egypt (Gharbia, Dakahlya, Kafr El sheikh, Zagazig and Domietta) was carried out. All flocks were vaccinated against IBD virus. RT-PCR revealed successful amplification of 620 bp of VP2 in 17 out of 20 samples (85%). VP2 gene nucleotide sequence analysis of six IBDV isolates (F342-1, F342-2, F342-4, F342-5 and F342-7) revealed 99.1 % similarity to the Giza 2000, Giza 2008 vv, SV-G1, SV-G2, SV-G4 and SV-G5 which were very virulent IBDV strains while the isolate F342-3 was close to D78 classical vaccinal strain and Kal 2001 classical IBDV strain variant.

Spatiotemporal Phylogenetic Analysis and Molecular Characterisation of Infectious Bursal Disease Viruses Based on the VP2 Hyper-Variable Region

Background

Infectious bursal disease is a highly contagious and acute viral disease caused by the infectious bursal disease virus (IBDV); it affects all major poultry producing areas of the world. The current study was designed to rigorously measure the global phylogeographic dynamics of IBDV strains to gain insight into viral population expansion as well as the emergence, spread and pattern of the geographical structure of very virulent IBDV (vvIBDV) strains.

Methodology/Principal Findings

Sequences of the hyper-variable region of the VP2 (HVR-VP2) gene from IBDV strains isolated from diverse geographic locations were obtained from the GenBank database; Cuban sequences were obtained in the current work. All sequences were analysed by Bayesian phylogeographic analysis, implemented in the Bayesian Evolutionary Analysis Sampling Trees (BEAST), Bayesian Tip-association Significance testing (BaTS) and Spatial Phylogenetic Reconstruction of Evolutionary Dynamics (SPREAD) software packages. Selection pressure on the HVR-VP2 was also assessed. The phylogeographic association-trait analysis showed that viruses sampled from individual countries tend to cluster together, suggesting a geographic pattern for IBDV strains. Spatial analysis from this study revealed that strains carrying sequences that were linked to increased virulence of IBDV appeared in Iran in 1981 and spread to Western Europe (Belgium) in 1987, Africa (Egypt) around 1990, East Asia (China and Japan) in 1993, the Caribbean Region (Cuba) by 1995 and South America (Brazil) around 2000. Selection pressure analysis showed that several codons in the HVR-VP2 region were under purifying selection.

Conclusions/Significance

To our knowledge, this work is the first study applying the Bayesian phylogeographic reconstruction approach to analyse the emergence and spread of vvIBDV strains worldwide.

Rapid and sensitive detection of infectious bursal disease virus by reverse transcription loop-mediated isothermal amplification combined with a lateral flow dipstick

Infectious bursal disease (IBD), an immunosuppressive disease that affects all ages of chickens, results in significant losses in the poultry industry. A reverse transcription loop-mediated isothermal amplification (RT-LAMP) combined with a chromatographic lateral flow dipstick (LFD) for the detection of infectious bursal disease virus (IBDV) was developed. The whole process of testing can be completed in less than 70 min using biotin-labeled primers, an FITC-labeled DNA probe, and the LFD. The detection limits for IBDV using RT-LAMP and RT-LAMP-LFD were the same at 10(-1)plaque forming units (PFU). When other unrelated viruses and cells were tested, no false positive results were observed. In addition, the amplification efficiency of RT-LAMP was enhanced when a loop primer was used. The RT-LAMP-LFD product started to be detected after 40 min. Clinical samples were used to compare assays using RT-PCR, nested RT-PCR, RT-LAMP, and RT-LAMP-LFD and the positive rates were 16%, 40%, 40%, and 40%, respectively. In conclusion, this assay is an easy, rapid, accurate, and sensitive method for the detection of IBDV and will improve the screening of field samples, especially when veterinarians have limited resources.

Sequencing and phylogenetic analysis of the infectious bursal disease virus isolates from outbreak in layer flocks in the state of Minas Gerais

Sequencing and phylogenetic analysis based on the nucleotide sequence of the gene encoding VP2 protein was carried out in order to characterize the agent of two outbreaks of infectious bursal disease in layer flocks in the state of Minas Gerais in 2004. The results indicate the outbreaks could be related to the vaccinal virus.

Comparative study of the replication of infectious bursal disease virus in DF-1 cell line and chicken embryo fibroblasts evaluated by a new real-time RT-PCR

A real-time RT-PCR method was developed for the detection of infectious bursal disease virus (IBDV). The VP5 gene of IBDV was chosen as the target binding region for a specific TaqMan probe. The results showed that viral genomic copy number could be quantified accurately ranging from 10(8)copies/microL to 10(1)copies/microL. No positive signal was detected for other avian pathogens in the specificity test. This assay was highly sensitive and could detect as little as 30 copies of viral RNA. Both the coefficients of variation (CVs) of inter- and intra-assay reproducibility were less than 2%. Growth curves of the IBDV Gt strain in chicken embryo fibroblasts (CEF) and DF-1 cells were evaluated by the real-time RT-PCR. The data showed that the cytopathic effects of the virus in CEF and DF-1 cells were similar. However, higher viral titers were detected in the DF-1 cell line. This study indicated that the real-time RT-PCR approach provided a powerful diagnostic tool with high sensitivity and specificity for the identification and quantitation of IBDV. The DF-1 cell line may be a more suitable continuous cell line for the propagation of IBDV compared to CEF.

Molecular characterisation of infectious bursal disease viruses isolated in recent acute outbreaks in Slovenia

In 2004 and then in 2006 several outbreaks of infectious bursal disease (IBD) were reported in broiler and broiler breeder flocks in Slovenia. In this report ten recently emerged IBD viruses (IBDV) were characterised by sequence analysis of the VP2 hypervariable region and compared to previous Slovene IBDV strains from 1995/1996 and to some representative serotype 1 IBDV strains of different pathotypes. On the basis of nucleotide and amino acid identities, phylogenetic analyses and the presence of very virulent IBDV (vvIBDV) conserved amino acid substitutions, all Slovene isolates from recent outbreaks were identified as vvIBDV. Although some unique nucleotide exchanges and amino acid substitutions have been observed, the results of this study indicated that recent vvIBDV isolates are closely related with those from outbreaks in the 1990s. However, acute IBD has not been reported in commercial flocks in Slovenia for some years. This could lead to the conclusion that poor biosecurity and relaxed vaccination could be responsible for the re-emergence of vvIBDV.

Molecular studies on suspect very virulent infectious bursal disease virus genomic RNA samples

Infectious bursal disease (IBD) associated with high mortality was first observed in Europe in the mid-1980s. The viruses identified in those outbreaks were described as being very virulent infectious bursal disease virus (vvIBDV) strains. These viruses have spread to nearly every continent but have not yet been identified in North America, Australia, and New Zealand. There is a real and immediate concern that the very virulent form of IBDV will continue to spread until it is present on every continent. Genomic RNA samples from IBDV strains suspected of being very virulent were submitted to our laboratory for molecular analysis. Nucleotide sequences of the VP2 gene hypervariable sequence region were determined for 18 of these viruses. A comparison with published vvIBDV sequences indicated that all but one sample (Thai 4) had nucleotide and predicted amino acid sequences consistent with vvIBDV strains. Published sequences and the nucleotide sequences of our 17 putative vvIBDV strains were used to identify unique nucleotides in the VP2 gene. Probe pairs for a real-time reverse transcriptase-polymerase chain reaction (RT-PCR) assay were designed based on these unique sequences and then used to test the 17 genomic samples that were identified by nucleotide sequencing to be consistent with vvIBDV, plus the one Thai 4 sample that was not consistent with vvIBDV. Using melting temperature (Tm) analysis following real-time RT-PCR, two probe pairs (vv232 and vv256) successfully identified the 17 putative vvIBDV strains and distinguished them from the Thai 4 sample. An additional 26 genomic RNA samples submitted as suspect vvIBDV strains were then tested using the vv232 and vv256 probes. Based on the melting point analysis of these two probes, all 26 samples contained nucleotide sequences consistent with vvIBDV strains. The specificity of the vv232 and vv256 probe pairs was evaluated using 19 non-vvIBDV strains. In every case, the probes distinguished the 19 classic and variant (non-vvIBDV) strains from the putative vvIBDV strains. Diagnostic assays that can reliably identify vvIBDV strains are needed for surveillance programs designed to monitor the spread of these viruses.

Real-time RT-PCR differentiation and quantitation of infectious bursal disease virus strains using dual-labeled fluorescent probes

A real-time RT-PCR assay was developed utilizing dual-labeled fluorescent probes binding to VP4 sequence that are specific to the classical (Cl), variant (V) and very virulent (vv) strains of infectious bursal disease virus (IBDV). The assay was highly sensitive and could detect as little as 3 x 10(2) to 3 x 10(3) copies of viral template. Viral genomic copy number could be accurately assayed over a broad range of 7-8 logs of viral genome. The variant sequence-specific probe was found to be highly specific in detecting isolates classified as variant A, D, E, G and GLS-5, and did not react with classical strains. A total of 130 field and experimental variant strain isolates were tested using this assay. The classical sequence-specific probe also demonstrated high sensitivity and specificity, and positively detected a total of 87 STC isolates, both field and experimental isolates, while differentiating between isolates that were variant and classical strains. The very virulent sequence-specific probe detected positively the Holland vvIBDV isolate and did not react with classical or variant strains. Rapid identification of viral strain is a primary concern to poultry flock health programs to ensure administered vaccines will protect against current strains of virus circulating in the flock. The ability to quantify virus concurrently is also of assistance in identifying the progression of disease outbreaks within the flock.

Secreted expression of the VP2 protein of very virulent infectious bursal disease virus in the methylotrophic yeast Pichia pastoris

The VP2-encoding gene of very virulent infectious bursal disease virus (vvIBDV) was amplified using reverse transcription (RT)-polymerase chain reaction (PCR) and inserted into pPICZalphaA vector. Recombinant plasmid DNA was integrated into the chromosome of the transformed Pichia pastoris by electroporation and expressed protein identified by SDS-PAGE and Western blotting. High-level secreted expression was performed by determining the Mut+ phenotype and secreting multi-copy integrants in the recombinant yeast. A recombinant protein of approximately 67 kDa was secreted into the supernatant from the yeast when induced with methanol. The expressed supernatant was bound with chicken anti-IBDV polyclonal antibodies. Western blotting with antibodies against vvIBDV indicated that the recombinant VP2 protein retained its antigenicity. High-level production (10 mg/100 ml) of the recombinant VP2 protein indicated that P. pastoris was an efficent expression system for vvIBDV VP2 protein.

Differentiation of infectious bursal disease viruses isolated in Croatia

Infectious bursal disease viruses (IBDVs) in 26 IBDV-positive bursa samples collected in Croatia during the period 1996-2000 and in two commercially available vaccines were differentiated by the presence or absence of the CfoI, SacI, SspI, StuI, and TaqI restriction sites in the 422-bp fragment of segment A of the VP2 gene (nt 732-1153). The fragments from 14 (54%) field isolates were TaqI+ StuI+ SspI+ and SacI- CfoI-, indicating their very virulent (vv) character. The presence of CfoI restriction site in 10 (38%) field isolates is uncommon for vvIBDV strains. It was detected in only the 88180 vvIBDV strain. Nevertheless, these isolates can be classified as vv strains according to TaqI+ StuI+ SspI+ SacI- restrictions. Two SacI+ StuI+ CfoI+ TaqI- SspI- field isolates (8%) could be classified as non-vvIBDVs. The StuI+ restriction is common to vvIBDV strains. However, the StuI recognition sequence is present in the F52/70 classic European and 002-73 attenuated strains as well. The SacI+ CfoI+ StuI- SspI- restrictions and the lack of the TaqI restriction at nt position 832 show that the IBDV in GUMBOKAL IM-SPF vaccine corresponds to the attenuated and/or vaccine strains. The TaqI restriction at nt position 875 suggests that the IBDV in GUMBOKAL SPF vaccine could belong to the mild strains.