Pathogenicity and Molecular Analysis of an Infectious Bursal Disease Virus Isolated from Malaysian Village Chickens

Comparative Pathogenicity of Malaysian variant and very virulent infectious bursal disease viruses in chickens

Variant infectious bursal disease virus (vaIBDV) has been identified in various countries with significant economic losses. Recently, the first identification of variant strain in Malaysia was reported. The pathogenicity of the Malaysian variant, UPM1432/2019 and very virulent infectious bursal disease virus (vvIBDV), UPM1056/2018 strains were comparatively evaluated in specific-pathogen-free (SPF) chickens based on gross and histopathological examinations and viral load. Four-week-old SPF chickens were randomly divided into 3 groups; Group 1 served as the control, while groups 2 and 3 birds were challenged with the vaIBDV and vvIBDV, respectively. Three birds from each group were weighed, euthanised and necropsied at 2-, 3-, 4-, 5-, 7- and 21-days post-challenge (dpc). Unlike UPM1056/2018 group, birds from UPM1432/2019 group did not show clinical signs or death. UPM1056/2018 strain caused 11% mortality rate in the infected chickens. The bursal body index (BBIX) for UPM1432/2019- and UPM1056/2018 groups was < 0.7 from 2 dpc and continued to decrease to 0.49 and 0.45, respectively at 21 dpc. UPM1432/2019 strain was more persistent in the bursa than UPM1056/2018 strain. Both strains induced similar pathological lesions in SPF chicks. These results indicate that the Malaysian vaIBDV severely damaged the immune organs of chickens and was more persistent in bursal tissue than vvIBDV. The study provides insight into the pathogenicity of the variant strain as further study may be required to evaluate the efficacy of the current available IBD vaccines in Malaysia against the strain.

Genetic Diversity of Recent Infectious Bursal Disease Viruses Isolated From Vaccinated Poultry Flocks in Malaysia

Vaccination is an essential component in controlling infectious bursal disease (IBD), however, there is a lack of information on the genetic characteristics of a recent infectious bursal disease virus (IBDV) that was isolated from IBD vaccinated commercial flocks in Malaysia. The present study investigated 11 IBDV isolates that were isolated from commercial poultry farms. The isolates were detected using reverse transcription-polymerase chain reaction (RT-PCR) targeting the hypervariable region (HVR) of VP2. Based on the HVR sequences, five isolates (IBS536/2017, IBS624/2017, UPM766/2018, UPM1056/2018, and UPM1432/2019) were selected for whole-genome sequencing using the MiSeq platform. The nucleotide and amino acid (aa) sequences were compared with the previously characterized IBDV strains. Deduced aa sequences of VP2HVR revealed seven isolates with 94–99% aa identity to very virulent strains (genogroup 3), two isolates with 97–100% aa identity to variant strains (genogroup 2), and two strains with 100% identity to the vaccine strain (genogroup 1) of IBDV. The phylogenetic analysis also showed that the isolates formed clusters with the respective genogroups. The characteristic motifs 222T, 249K, 286I, and 318D are typical of the variant strain and were observed for UPM1219/2019 and UPM1432/2019. In comparison, very virulent residues such as 222A, 249Q, 286T, and 318G were found for the vvIBDV, except for the UPM1056/2018 strain with a A222T substitution. In addition, the isolate has aa substitutions such as D213N, G254D, S315T, S317R, and A321E that are not commonly found in previously reported vvIBDV strains. Unlike the other vvIBDVs characterized in this study, UPM766/2018 lacks the MLSL aa residues in VP5. The aa tripeptides 145/146/147 (TDN) of VP1 were conserved for the vvIBDV, while a different motif, NED, was observed for the Malaysian variant strain. The phylogenetic tree showed that the IBDV variant clustered with the American and Chinese variant viruses and are highly comparable to the novel Chinese variants, with 99.9% identity. Based on the sequences and phylogenetic analyses, this is the first identification of an IBDV variant being reported in Malaysia. Further research is required to determine the pathogenicity of the IBDV variant and the protective efficacy of the current IBD vaccines being used against the virus.

A Review of Pathogen Transmission at the Backyard Chicken-Wild Bird Interface

Habitat conversion and the expansion of domesticated, invasive species into native habitats are increasingly recognized as drivers of pathogen emergence at the agricultural-wildlife interface. Poultry agriculture is one of the largest subsets of this interface, and pathogen spillover events between backyard chickens and wild birds are becoming more commonly reported. Native wild bird species are under numerous anthropogenic pressures, but the risks of pathogen spillover from domestic chickens have been historically underappreciated as a threat to wild birds. Now that the backyard chicken industry is one of the fastest growing industries in the world, it is imperative that the principles of biosecurity, specifically bioexclusion and biocontainment, are legislated and implemented. We reviewed the literature on spillover events of pathogens historically associated with poultry into wild birds. We also reviewed the reasons for biosecurity failures in backyard flocks that lead to those spillover events and provide recommendations for current and future backyard flock owners.

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.

Bursal immunopathology responses of specific-pathogen-free chickens and red jungle fowl infected with very virulent infectious bursal disease virus

Very virulent infectious bursal disease virus (vvIBDV) targets B lymphocytes in the bursa of Fabricius (BF), causing immunosuppression and increased mortality rates in young birds. There have been few studies on the host immune response following vvIBDV infection at different inoculum doses in chickens with different genetic backgrounds. In this study, we characterized the immune responses of specific-pathogen-free (SPF) chickens and Malaysian red jungle fowl following infection with vvIBDV strain UPM0081 at 10^3.8 and 10^6.8 times the 50% embryo infectious dose (EID₅₀). The viral burden, histopathological changes, immune cell populations, and expression of immune-related genes were measured and compared between infected and uninfected bursa at specific intervals. The populations of KUL1⁺, CD3⁺CD4⁺ and CD3⁺CD8⁺ cells were significantly increased in both types of chickens at 3 dpi, and there was significant early depletion of IgM⁺ B cells at 1 dpi in the red jungle fowl. vvIBDV infection also induced differential expression of genes that are involved in Th1 and pro-inflammatory responses, with groups receiving the higher dose (10^6.8 EID₅₀) showing earlier expression of IFNG, IL12B, IL15, IL6, CXCLi2, IL28B, and TLR3 at 1 dpi. Although both chicken types showed equal susceptibility to infection, the red jungle fowl were clinically healthier than the SPF chickens despite showing more depletion of IgM⁺ B cells and failure to induce IFNB activation. In conclusion, high-dose vvIBDV infection caused an intense early host immune response in the infected bursa, with depletion of IgM⁺ B cells, bursal lesions, and cytokine expression as a response to mitigate the severity of the infection.

Adaptation and Molecular Characterization of Two Malaysian Very Virulent Infectious Bursal Disease Virus Isolates Adapted in BGM-70 Cell Line

Two Malaysian very virulent infectious bursal disease virus (vvIBDV) strains UPM0081 and UPM190 (also known as UPMB00/81 and UPM04/190, respectively) isolated from local IBD outbreaks were serially passaged 12 times (EP12) in specific pathogen free (SPF) chicken embryonated eggs (CEE) by chorioallantoic membrane (CAM) route. The EP12 isolate was further adapted and serially propagated in BGM-70 cell line up to 20 passages (P20). Characteristic cytopathic effects (CPEs) were subtly observed at P1 in both isolates 72 hours postinoculation (pi). The CPE became prominent at P5 with cell rounding, cytoplasmic vacuoles, granulation, and detachment from flask starting from day 3 pi, up to 7 days pi with titers of 10^9.50 TCID₅₀/mL and log10^9.80 TCID₅₀/mL for UPM0081 and UPM190, respectively. The CPE became subtle at P17 and disappeared by P18 and P19 for UPM0081 and UPM190, respectively. However, the presence of IBDV was confirmed by immunoperoxidase, immunofluorescence, and RT-PCR techniques. Phylogenetic analysis showed that these two isolates were of the vvIBDV. It appears that a single mutation of UPM190 and UPM0081 IBDV isolates at D279N could facilitate vvIBDV strain adaptability in CEE and BGM-70 cultures.

Characterization of Chicken Splenic-Derived Dendritic Cells Following Vaccine and Very Virulent Strains of Infectious Bursal Disease Virus Infection

Studies have shown that infectious bursal disease virus (IBDV) infects lymphoid cells, mainly B cells and macrophages. This study was aimed to examine the involvement of chicken splenic-derived dendritic cells (ch-sDCs) in specific-pathogen-free chickens following inoculation with IBDV vaccine strain (D78) and a very virulent (vv) strain (UPM0081). Following IBDV infection, enriched activated ch-sDCs were collected by using the negative selection method and were examined based on morphology and immunophenotyping to confirm the isolation method for dendritic cells (DCs). The presence of IBDV on enriched activated ch-sDCs was analyzed based on the immunofluorescence antibody test (IFAT), flow cytometry, and quantitative real-time PCR (RT-qPCR) while the mRNAs of several cytokines were detected using RT-qPCR. The isolated ch-sDCs resembled typical DC morphologies found in mammals by having a veiled shape and they grew in clusters. Meanwhile, the expression of DC maturation markers, namely CD86 and MHCII, were increased at day 2 and day 3 following vvIBDV and vaccine strain inoculation, respectively, ranging from 10% to 40% compared to the control at 2.55% (P < 0.05). At day 3 postinfection, IBDV VP3 proteins colocalized with CD86 were readily detected via IFAT and flow cytometry in both vaccine and vvIBDV strains. In addition, enriched activated ch-sDCs were also detected as positive based on the VP4 gene by RT-qPCR; however, a higher viral load was detected on vvIBDV compared to the vaccine group. Infection with vaccine and vvIBDV strains induced the enriched activated ch-sDCs to produce proinflammatory cytokines and Th1-like cytokines from day 3 onward; however, the expressions were higher in the vvIBDV group (P < 0.05). These data collectively suggest that enriched activated ch-sDCs were permissive to IBDV infection and produced a strong inflammatory and Th1-like cytokine response following vvIBDV infection as compared to the vaccine strain.

In vitro characterization of chicken bone marrow-derived dendritic cells following infection with very virulent infectious bursal disease virus

Infectious bursal disease is caused by infectious bursal disease virus (IBDV), an immunosuppressive virus that targets immune cells such as B cells and macrophages. However, the involvement of dendritic cells (DCs) during IBDV infection is not well understood. In this study the in vitro effects of live and inactivated very virulent IBDV (vvIBDV) UPM0081 on bone marrow-derived DCs (BM-DC) were characterized and compared with BM-DC treated with lipopolysaccharide (LPS). Morphologically, BM-DC treated with LPS and vvIBDV showed stellate shape when compared to immature BM-DC. In addition, LPS-treated and both live and inactivated vvIBDV-infected BM-DC expressed high levels of double positive CD86 and major histocompatibility complex class II antigens (>20%). vvIBDV-infected BM-DC showed significantly higher numbers of apoptotic cells compared to LPS. Replication of vvIBDV was detected in the infected BM-DC as evidenced by the increased expression of VP3 and VP4 IBDV antigens based on flow cytometry, real-time polymerase chain reaction and immunofluorescence tests. Levels of different immune-related genes such as interleukin-1β (IL-1β), CXCLi2 (IL-8), IL-18, interferon gamma (IFN-γ, IL-12α, CCR7 and Toll-like receptor-3 (TLR3) were measured after LPS and vvIBDV treatments. However, marked differences were noticed in the onset and intensity of the gene expression between these two treatment groups. LPS was far more potent than live and inactivated vvIBDV in inducing the expression of IL-1β, IL-18 and CCR7 while expression of Th1-like cytokines, IFN-γ and IL-12α were significantly increased in the live vvIBDV treatment group. Meanwhile, the expression of TLR3 was increased in live vvIBDV-infected BM-DC as compared to control. Inactivated vvIBDV-treated BM-DC failed to stimulate IFN-γ, IL-12α and TLR3 expressions. This study suggested that BM-DC may serve as another target cells during IBDV infection which require further confirmation via in vivo studies.

Evaluation of infectious bursal disease virus stability at different conditions of temperature and pH

Infectious bursal disease (IBD) is one of the highly pathogenic viral diseases of poultry. The disease poses a serious threat to the economy of many developing countries where agriculture serves as the primary source of national income. Infectious bursal disease virus (IBDV) belongs to the family Birnaviridae. The IBDV is well characterized to cause immunosuppression in poultry. The live attenuated vaccine is the only way to protect the chickens from IBDV infection. The ineffectiveness of vaccine is one of the major causes of IBDV outbreaks in field condition. In the present study, we discuss briefly about the biology of IBDV genome and its proteins under different conditions of temperature and pH in order to evaluate its infectivity under adverse physical conditions. Our results indicate that the IBDV is non-infective above 42 °C and unstable above 72 °C. However, the change in pH does not significantly contribute to the IBDV stability. The study will be useful in estimating an optimum storage condition for IBDV vaccines without causing any deterioration in its viability and effectiveness.

Differential modulation of immune response and cytokine profiles in the bursae and spleen of chickens infected with very virulent infectious bursal disease virus

Background

Very virulent infectious bursal disease virus (vvIBDV) induces immunosuppression and inflammation in young birds, which subsequently leads to high mortality. In addition, infectious bursal disease (IBD) is one of the leading causes of vaccine failure on farms. Therefore, understanding the immunopathogenesis of IBDV in both the spleen and the bursae could help effective vaccine development. However, previous studies only profiled the differential expression of a limited number of cytokines, in either the spleen or the bursae of Fabricius of IBDV-infected chickens. Thus, this study aims to evaluate the in vitro and in vivo immunoregulatory effects of vvIBDV infection on macrophage-like cells, spleen and bursae of Fabricius.

Results

The viral load was increased during the progression of the in vitro infection in the HD11 macrophage cell line and in vivo, but no significant difference was observed between the spleen and the bursae tissue. vvIBDV infection induced the expression of pro-inflammatory and Th1 cytokines, and chemokines from HD11 cells in a time- and dosage-dependent manner. Furthermore, alterations in the lymphocyte populations, cytokine and chemokine expression, were observed in the vvIBDV-infected spleens and bursae. A drastic rise was detected in numbers of macrophages and pro-inflammatory cytokine expression in the spleen, as early as 2 days post-infection (dpi). On 4 dpi, macrophage and T lymphocyte infiltration, associated with the peak expression of pro-inflammatory cytokines in the bursae tissues of infected chickens were observed. The majority of the significantly regulated pro-inflammatory cytokines and chemokines, in vvIBDV-infected spleens and bursae, were also detected in vvIBDV-infected HD11 cells. This cellular infiltration subsequently resulted in a sharp rise in nitric oxide (NO) and lipid peroxidation levels.

Conclusion

This study suggests that macrophage may play an important role in regulating the early expression of pro-inflammatory cytokines, first in the spleen and then in the bursae, the latter tissue undergoing macrophage infiltration at 4 dpi.

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.

Identification of infectious bursal disease viruses from RNA extracted from paraffin-embedded tissue

After histopathologic screening of bursas of Fabricius for the presence of infectious bursal disease virus (IBDV) lesions, the hypervariable region of the VP2 gene for IBDV was extracted from formalin-fixed paraffin-embedded tissue blocks. With real-time reverse transcription-polymerase chain reaction (RT-PCR) and sequencing, IBDV was identified in 227 different blocks. The ability to identify the actual virus strain associated with the lesions observed microscopically in the bursa of Fabricius allowed for direct correlation between viral identity and lesions, which may help in designing vaccination strategies. Several new emerging viruses that do not group with other known IBDVs in phylogenetic tree analysis were identified, as well as a unique variant virus that had 63 nucleotides missing from its hypervariable region.

Economically important non-oncogenic immunosuppressive viral diseases of chicken--current status

Immunosuppressive viral diseases threaten the poultry industry by causing heavy mortality and economic loss of production, often as a result of the chickens' increased susceptibility to secondary infections and sub-optimal response to vaccinations. This paper aimed to present an up-to-date review of three specific economically important non-oncogenic immunosuppressive viral diseases of chickens, viz. chicken infectious anaemia (CIA), infectious bursal disease (IBD) and hydropericardium syndrome (HPS), with emphasis on their immunosuppressive effects. CIA and IBD causes immunosuppression in chickens and the socio-economic significance of these diseases is considerable worldwide. CIA occurs following transovarian transmission of chicken anaemia virus and has potential for inducing immunosuppression alone or in combination with other infectious agents, and is characterized by generalized lymphoid atrophy, increased mortality and severe anemia. The virus replicates in erythroid and lymphoid progenitor cells, causing inapparent, sub-clinical infections that lead to depletion of these cells with consequent immunosuppressive effects. The IBD virus replicates extensively in IgM(+) cells of the bursa and chickens may die during the acute phase of the disease, although IBD virus-induced mortality is highly variable and depends, among other factors, upon the virulence of the virus strain. The sub-clinical form is more common than clinical IBD because of regular vaccination on breeding farms. Infection at an early age significantly compromises the humoral and local immune responses of chickens because of the direct effect of B cells or their precursors. HPS is a recently emerged immunosuppressive disease of 3-6-weeked broilers, characterized by sudden onset, high mortality, typical hydropericardium and enlarged mottled and friable livers, with intranuclear inclusion bodies in the hepatocytes. The agent, fowl adenovirus-4, causes immunosuppression by damaging lymphoid tissues; the presence of IBD and CIA viruses may predispose for HPS or HPS may predispose for other viral infections. Synergism with CIA or other virus infections or prior immunosuppression is necessary to produce IBH-HPS in chickens and the susceptibility of chickens infected with fowl adenovirus varies throughout the course of CIA infection. The mechanism of immunosuppression has been studied in detail for certain chicken viruses at molecular levels, which will provides new opportunities to control these diseases by vaccination.