Pathological effect of different avian infectious bronchitis virus strains on the bursa of Fabricius of chickens.

Infectious bronchitis is an acute and highly contagious disease caused by avian infectious bronchitis virus (IBV). As well as the typical clinical respiratory signs, such as dyspnoea and tracheal rales, QX genotype strains can also cause damage to the urinary system and reproductive system. Our previous studies found that chickens infected with QX-type IBV also displayed damage to the bursa of Fabricius. To investigate the effects of different genotypes of IBV on the bursa of Fabricius, we challenged one-week-old SPF chickens with Mass, QX and TW genotype IBV strains and compared the clinical signs, gross lesions, histopathological damage, viral loads, and expression levels of inflammatory cytokines (IL-6, IL-8, IL-1ß, IFN-α,ß, γ and TNF-α). The results showed that all three strains caused tissue damage, while significant temporal variations in the viral loads of the different infected groups were detected. IBV infection seriously interfered with the natural immune response mediated by inflammatory cytokines (IFN-α, IFN-ß, IL-6 and IFN-γ) in chickens. Our results suggested that IBV has potential immunological implications for chickens that may lead to poor production efficiency. RESEARCH HIGHLIGHTSAvian coronavirus IBV is an important pathogen of chickens.IBV has potential immunological implications in chickens.The bursal viral load of different IBV strains varies significantly.

Molecular Characterization and Demographic Study on Infectious Bursal Disease Virus in Faisalabad District.

The re-emergence of virulent strains of the Infectious Bursal Disease Virus (IBDV) leads to significant economic losses of poultry industry in Pakistan during last few years. This disease causes the infection of bursa, which leads to major immune losses. A total number of 30 samples from five IBD outbreaks during the period of 2019-20 were collected from different areas of Faisalabad district, Pakistan and assayed by targeting the IBD virus VP2 region through RT-PCR. Among all the outbreaks, almost 80% of poultry birds were found positive for the IBDV. The bursa tissues were collected from the infected birds and histopathological examination of samples revealed severe lymphocytic depletion, infiltration of inflammatory cells, and necrosis of the bursa of Fabricius (BF). Positive samples were subjected to re-isolation and molecular characterization of IBDV. The Pakistan IBDV genes were subjected to DNA sequencing to determine the virus nucleotide sequences. The sequences of 100 Serotype-I IBDVs showing nearest homology were compared and identified with the study sequence. The construction of the phylogenetic tree for nucleotide sequences was accomplished by the neighbor-joining method in MEGA-6 with reference strains. The VP2 segment reassortment of IBDVs carrying segment A were identified as one important type of circulating strains in Pakistan. The findings indicated the molecular features of the Pakistan IBDV strains playing a role in the evolution of new strains of the virus, which will contribute to the vaccine selection and effective prevention of the disease.

Effect of TMUV on immune organs of TMUV infected ducklings.

Tembusu Virus (TMUV), a pathogenic member of Flavivirus family, acts as the causative agent of egg-laying and has severely threatened the duck industry over the past few years. Thus far, the pathogenicity of such virus has been extensively studied, whereas TMUV on immune system has been less comprehensively assessed, especially on ducklings that exhibit more susceptible to TMUV attack. Accordingly, in the present study, 5-day-old ducklings were infected with TMUV-TC2B (104 TCID50) via intravenous injection, and mock ones were inoculated with phosphate-buffered saline (PBS) in identical manner as control. At 1 day-post inoculation (dpi), the innate immunity was strongly activated, and reacted rapidly to TMUV invasion, which was reflected as the significantly up-regulated IFN-stimulated genes (ISGs), especially in immune organs (e.g., thymus, bursa of Fabricius (BF) and spleen). Subsequently, under the continuous monitoring, the levels of IgA, IgM and IgG acting as the representative immunoglobulins (Igs) were constantly higher than those of mock ducklings, demonstrating that humoral immunity also played a major role in anti-virus infection. Despite the immune system activated positively, TMUV still caused systemic infection, and in particular, the immune organs were subject to severe damage in the early infection. With our constant observation, the injury of spleen and BF turned out to be getting more serious, and at 6 dpi, TMUV antigen was widely detected in both of two immune organs by immunohistochemistry (IHC) and main histopathological lesion presented as lymphocytopenia. Moreover, the elevated apoptosis rate of splenic lymphocytes and the alteration of immune organ index also revealed the damage of lymphoid organs and similarly, it is worth noting that severe damages were detected in thymus of TMUV-infected ducklings as well. In brief, the present study systematically described the dynamic damage of immune system after being attacked by TMUV and presented insights into the research of pathogenicity.

Full-length genome sequencing of a very virulent infectious bursal disease virus isolated in Tunisia.

Infectious bursal disease (IBD), an acute, highly contagious, and immunosuppressive avian disease, is caused by infectious bursal disease virus (IBDV) and constitutes one of the main threats to the poultry industry, worldwide. This study was performed to isolate and characterize IBDV isolates circulating in Tunisia. Eleven collected bird samples were identified using an SYBR Green-based one-step real-time reverse transcriptase polymerase chain reaction. The full-length genome sequencing of 7 of the 11 IBDV isolates has been realized. VP2 gene data showed limited sequence variations for all the 7 tested samples. The few nucleotide changes were silent and the deduced amino acid sequences were identical with the exception of a unique and characteristic nonsilent mutation (C1203) detected for the TN37/19 isolate, with a change of amino acid (L) to (F) at position 401. In addition, the serine-rich heptapeptide SWSASGS, characteristic of virulent IBDV, as well the amino acid residues, conserved in most very virulent IBDV (vvIBDV) strains, were detected in all the Tunisian tested isolates. Nucleotide sequences of VP5 gene revealed the presence of 5 substitutions leading to changes in the amino acid sequences of the virus. Two of these mutations were unique and characteristic of the Tunisian isolates. Besides, the alternative AUG start codon, characteristic of vvIBDV, was observed in all obtained VP5 gene sequences. The Tunisian protein sequences of VP1 showed E242 and the TDN triplet at positions 145, 146, and 147, a motif specific of vvIBDV. Phylogenetic analyses of the 5 genes confirmed the sequence alignment results and showed that the Tunisian strains are closely related to the very virulent Algerian IBDV strains.

The association between SAα2,3Gal occurrence frequency and avian influenza viral load in mallards (Anas platyrhynchos) and blue-winged teals (Spatula discors).

BACKGROUND: Individual heterogeneity in pathogen load can affect disease transmission dynamics; therefore, identifying intrinsic factors responsible for variation in pathogen load is necessary for determining which individuals are prone to be most infectious. Because low pathogenic avian influenza viruses (LPAIV) preferentially bind to alpha-2,3 sialic acid receptors (SAα2,3Gal) in the intestines and bursa of Fabricius in wild ducks (Anas and Spatula spp.), we investigated juvenile mallards (Anas platyrhyncos) and blue-winged teals (Anas discors) orally inoculated with A/northern pintail/California/44221-761/2006 (H5N9) and the virus titer relationship to occurrence frequency of SAα2,3Gal in the intestines and bursa. To test the natural variation of free-ranging duck populations, birds were hatched and raised in captivity from eggs collected from nests of free-ranging birds in North Dakota, USA. Data generated from qPCR were used to quantify virus titers in cloacal swabs, ileum tissue, and bursa of Fabricius tissue, and lectin histochemistry was used to quantify the occurrence frequency of SAα2,3Gal. Linear mixed models were used to analyze infection status, species, and sex-based differences. Multiple linear regression was used to analyze the relationship between virus titer and SAα2,3Gal occurrence frequency. RESULTS: In mallards, we found high individual variation in virus titers significantly related to high variation of SAα2,3Gal in the ileum. In contrast to mallards, individual variation in teals was minimal and significant relationships between virus titers and SAα2,3Gal were not determined. Collectively, teals had both higher virus titers and a higher occurrence frequency of SAα2,3Gal compared to mallards, which may indicate a positive association between viral load and SAα2,3Gal. Statistically significant differences were observed between infected and control birds indicating that LPAIV infection may influence the occurrence frequency of SAα2,3Gal, or vice versa, but only in specific tissues. CONCLUSIONS: The results of this study provide quantitative evidence that SAα2,3Gal abundance is related to LPAIV titers; thus, SAα2,3Gal should be considered a potential intrinsic factor influencing variation in LPAIV load.

Genome-wide analysis of differentially expressed mRNAs, lncRNAs, and circRNAs in chicken bursae of Fabricius during infection with very virulent infectious bursal disease virus.

BACKGROUND: Infectious bursal disease virus (IBDV) causes acute, highly contagious, immunosuppressive, and lethal infectious disease in young chickens and mainly infects the bursa of Fabricius (BF). To investigate interactions between IBDV and its host, RNA sequencing was applied to analyze the responses of the differentially expressed transcriptional profiles of BF infected by very virulent IBDV (vvIBDV). RESULTS: In total, 317 upregulated and 94 downregulated mRNAs were found to be significantly differentially expressed in infected chickens, compared to controls. Long non-coding RNA (lncRNA) and circular RNA (circRNA) alterations were identified in IBDV-infected chickens, and significantly different expression was observed in 272 lncRNAs and 143 circRNAs. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment analyses were performed to assess the functions of significantly dysregulated genes, which showed that the JAK-STAT signaling pathway, the NOD-like receptor signaling pathway, and apoptosis may be activated by IBDV infection. We predicted interactions between differentially expressed genes and produced lncRNA-mRNA and circRNA-miRNA-mRNA regulator network. CONCLUSIONS: The present study identified the expression profiles of mRNAs, lncRNAs, and circRNAs during vvIBDV infection and provides new insights into the pathogenesis of IBDV and antiviral immunity of the host.

Recombinant hemagglutinin glycoproteins provide insight into binding to host cells by H5 influenza viruses in wild and domestic birds.

Clade 2.3.4.4, H5 subtype highly pathogenic avian influenza viruses (HPAIVs) have caused devastating effects across wild and domestic bird populations. We investigated differences in the intensity and distribution of the hemagglutinin (HA) glycoprotein binding of a clade 2.3.4.4 H5 HPAIV compared to a H5 low pathogenic avian influenza virus (LPAIV). Recombinant HA from gene sequences from a HPAIV, A/Northern pintail/Washington/40964/2014(H5N2) and a LPAIV, A/mallard/MN/410/2000(H5N2) were generated and, via protein histochemistry, HA binding in respiratory, intestinal and cloacal bursal tissue was quantified as median area of binding (MAB). Poultry species, shorebirds, ducks and terrestrial birds were used. Differences in MAB were observed between the HPAIV and LPAIV H5 HAs. We demonstrate that clade 2.3.4.4 HPAIV H5 HA has a broader host cell binding across a variety of bird species compared to the LPAIV H5 HA. These findings support published results from experimental trials, and outcomes of natural disease outbreaks with these viruses.

Identification of Newcastle disease virus P-gene editing using next-generation sequencing.

Avian paramyxoviruses 1 has the ability to edit its P gene to generate three amino-coterminal proteins (P, V and W), but its kinetic change is unclear. In this study, next-generation sequencing (NGS) was used to analyze the P-gene editing of Newcastle disease virus (NDV). Transcriptome analysis of chicken embryonic tissues and bursa of fabricius showed the P-gene editing frequencies were 45.46-52.70%. To investigate the rules of P-gene editing along time, the ratio of PVW was determined by PCR based deep sequencing at multiple time points in cells infected with velogenic and lentogenic strain respectively. The results confirmed similar editing frequencies with transcriptome data and the PVW ratios were stable along time among different NDVs, but had a greater V-gene transcript on velogenic strain infection (P<0.001), which were different from previous reports. Also, it was shown that the number of inserted G residues in P-derived transcripts was not limited to +9G, and +10G transcripts were identified. These results confirmed the NDV P-gene editing frequencies and provided a novel point of view on NDV P-gene editing with NDV virulence.

T cell subset profile and inflammatory cytokine properties in the gut-associated lymphoid tissues of chickens during infectious bursal disease virus (IBDV) infection.

While infectious bursal disease virus (IBDV) mainly targets immature B cells and causes T cell infiltration in the bursa of Fabricius (BF) of chickens, the effect of IBDV infection on the properties of T cells and relevant cytokine production in avian gut-associated lymphoid tissues (GALTs) remains unknown. Here, we show that while the CD8+ T cell subset is not affected, IBDV infection decreases the percentage of CD4+ T cells in the cecal tonsil (CT), but not in esophagus tonsil, pylorus tonsil, and Meckel's diverticulum of GALTs, in contrast to BF and spleen, in which the proportion of CD4+ cells increases upon IBDV infection. Further, IBDV infection upregulates IFN-γ, IL-10, and the T cell checkpoint receptor LAG-3 mRNA expression in BF. In contrast, in CTs, IBDV infection significantly increases the production of IFN-ß and CTLA-4 mRNA, while no significant effect is seen in the case of IFN-γ, IL-10 and LAG-3. Together, our data reveal differential modulation of T cell subsets and proinflammatory cytokine production in different lymphoid tissues during the course of IBDV infection.

Effects of infectious bursal disease virus infection on interferon and antiviral gene expression in layer chicken bursa.

Layer chickens were artificially challenged with infectious bursal disease virus (IBDV), and the kinetics of IFN-λ and antiviral genes in the bursa were explored using quantitative real-time PCR. Data showed that after the chickens were infected with IBDV, the virus load in the bursa of the Fabricius peaked at 96 h and gradually decreased. The relative mRNA expression levels of IFN-λ and antiviral genes (zinc-finger antiviral protein [ZAP], interferon alpha-inducible protein 6 [IFI6], laboratory of genetics and physiology 2 [LGP2], virus inhibitory protein [Viperin], and Mx) of the infected group dramatically increased at 24-168 h compared with those of the negative-infected group. Furthermore, the ZAP mRNA expression peaked at 24 h (3.97-fold). The Viperin mRNA transcript level was highest at 48 h (384.60-fold). The mRNA expression levels of IFI6 (96.31-fold), LGP2 (18.29-fold), and Mx (88.85-fold) peaked at 72 h, and that of IFN-λ was most remarkable at 96 h (2978.81-fold). Furthermore, the ZAP change rule was significantly positively correlated with the change rule of the IBDV load. The mRNA expression levels of IFN-λ and antiviral genes (ZAP, IFI6, LGP2, Viperin, and Mx) increased as the virus expression increased and then decreased. These results further corroborated that the IBDV infection seriously interfered with the chicken's innate immune response.

Molecular survey of duck circovirus infection in poultry in southern and southwestern China during 2018 and 2019.

BACKGROUND: Duck circovirus (DuCV) is a potential immunosuppressive virus that causes feather disorders in young ducks. In this study, DuCV obtained from various species of ducks was investigated by polymerase chain reaction (PCR) in southern and southwestern China (Guangdong, Guangxi and Yunnan provinces) from 2018 to 2019. RESULTS: A total of 848 bursa samples were collected from dead Mulard, Cherry Valley Pekin, Muscovy and Mallard ducks from duck farms. The positivity rate of DuCV in the total sample was approximately 36.91%. We found that the prevalence of DuCV in Yunnan (43.09%) was higher than those in Guangxi (34.38%) and Guangdong (34.4%). However, the positivity rates of DuCV in the four duck species were not significantly different (P > 0.05). Nineteen randomly selected complete viral genomes were sequenced. The complete genomes of the DuCV were 1987 to 1995 nt in length, and were 81.7-99.3% homologous to the other 57 sequences in GenBank. Phylogenetic analyses based on the complete genomes of 76 DuCVs showed that the 19 novel DuCV sequences from Guangdong and Guangxi provinces mainly belonged to the DuCV-1 and DuCV-2 genetic groups, respectively. However, the two genotype groups coexisted in Yunnan Province. In addition, recombination analysis showed putative recombination sites in 3 strains in Yunnan that originated from strains Guangdong and Guangxi. Interestingly, the epidemiological investigation showed that Mulard ducks, Cherry Valley Pekin ducks and Muscovy ducks more than 4 weeks old were more susceptible to infection with the novel DuCV than ducks less than 4 weeks old. CONCLUSIONS: These data provide insight into the molecular epidemiology and genetic diversity of DuCVs circulating in southern and southwestern China for the first time.

Current state-of-the-art in the use of plants for the production of recombinant vaccines against infectious bursal disease virus.

Infectious bursal disease is a widely spread threatening contagious viral infection of chickens that induces major damages to the Bursa of Fabricius and leads to severe immunosuppression in young birds causing significant economic losses for poultry farming. The etiological agent is the infectious bursal disease virus (IBDV), a non-enveloped virus belonging the family of Birnaviridae. At present, the treatment against the spread of this virus is represented by vaccination schedules mainly based on inactivated or live-attenuated viruses. However, these conventional vaccines present several drawbacks such as insufficient protection against very virulent strains and the impossibility to differentiate vaccinated animals from infected ones. To overcome these limitations, in the last years, several studies have explored the potentiality of recombinant subunit vaccines to provide an effective protection against IBDV infection. In this review, we will give an overview of these novel types of vaccines with special emphasis on current state-of-the-art in the use of plants as "biofactories" (plant molecular farming). In fact, plants have been thoroughly and successfully characterized as heterologous expression systems for the production of recombinant proteins for different applications showing several advantages compared with traditional expression systems (Escherichia coli, yeasts and insect cells) such as absence of animal pathogens in the production process, improved product quality and safety, reduction of manufacturing costs, and simplified scale-up.

Evaluation of a novel inactivated vaccine against duck circovirus in muscovy ducks.

Duck circovirus (DuCV), an immunosuppressive pathogen, causes serious damage to waterfowls worldwide. A highly efficient vaccine would play a crucial role in preventing DuCV infections in the waterfowl breeding industry. However, to date, there is a dearth of commercial vaccines owing to the lack of a cell culture system for propagating the requisite virus amounts in vitro. In this study, we isolated DuCVs from Muscovy ducks, helped them proliferate using peripheral blood mononuclear cells (PBMCs), and developed an inactivated vaccine. Muscovy ducks vaccinated with the inactivated vaccine had higher neutralizing antibody titers than the control ducks and higher protection in the challenge experiment (as assessed by weight measurement). Moreover, the inactivated vaccine did not cause feather abnormalities, growth repression, and dwarf syndrome; likewise, lesions and lymphocyte apoptosis in the bursa of Fabricius, spleen, and thymus were not observed. Significantly lower virus shedding from the inactivated vaccine was detected up to 42 days post-inoculation. Together, these results suggest that the inactivated DuCV vaccine can induce a high immune response, is relatively safer for Muscovy ducks, and thus it is a protective vaccine candidates against DuCV infection.

Genotype-associated differences in bursal recovery after infectious bursal disease virus (IBDV) inoculation.

T-cell immune responses were shown to play an important role in the regulation of infectious bursal disease virus (IBDV) replication and development of lesions in the bursa of Fabricius (BF) (bursal lesions) but also in the recovery from the infection. Studies suggested that the host-genotype influences T-cell responses during the acute phase of infection. Genotype-related differences in the recovery phase were not investigated so far. The present study used commercial broiler- (BT), layer- (LT), dual-purpose type (DT) chicken lines as well as a specific pathogen free (SPF) LT chicken as a reference for comparison of T-cell related differences in IBDV-immunopathogenesis not only in the early phase post inoculation (pi) but also in the recovery phase. The Deventer formula was used to determine the optimal time point of inoculation with an intermediate plus IBDV strain when maternally derived antibody (MDA) titers were below the calculated breakthrough level of the virus for all genotypes. Differences in the bursal lesion development, intrabursal CD4+ and CD8+ T-cell accumulation and numbers of IBDV-positive cells were determined. In addition, anti-IBDV antibody development and the relative amount of anti-inflammatory cytokine mRNA were recorded until 28 days post IBDV inoculation. Differences between the genotypes were observed in the duration and magnitude of bursal lesions, CD4+ and CD8+ T-cell infiltration as well as the presence of anti-inflammatory Interleukin (IL)-10 and Transforming growth factor (TGF) ß4 cytokine mRNA (P < 0.05). While the investigated immune parameters were comparable between the genotypes at seven days pi, during 14, 21 and 28 days pi a delayed recovery process in LT and DT chickens compared to BT chickens was observed (P < 0.05). Furthermore, the age and residual MDA levels had a genotype-dependent influence on the onset of the anti-IBDV specific humoral and T-cell mediated immune responses. This study suggests, that the impact of T-cell immunity on the recovery process after IBDV infection may need to be considered further for the development of new breeding programs for disease resistant chicken lines.

Novel variants of infectious bursal disease virus can severely damage the bursa of fabricius of immunized chickens.

In recent years, atypical infectious bursal disease (IBD) with severe immunosuppression has brought new threats to the poultry industry and has caused considerable economic losses. Novel variant infectious bursal disease virus (IBDV) has been identified as the etiological pathogen and for unknown reasons is widespread in poultry on many chicken farms in China that have been immunized with vaccines against very virulent IBDV (vvIBDV). Using immunoprotection experiments in specific-pathogen-free chickens, we first verified that novel variant IBDV could severely damage the bursa of Fabricius of the important immune organ of immunized chicken in the presence of antibodies induced by three types of vvIBDV vaccines, which is a primary reason for the current epidemic of atypical IBD. Monoclonal antibody reactivity patterns and cross-neutralization assays further confirmed the obvious antigenic mismatch between novel variant IBDV and vvIBDV. Sequence analysis of the genome of novel variant IBDV (SHG19 strain) was performed and the key amino acid residues that might be involved in antigenicity and virulence differences of novel variant IBDV compared to vvIBDV were further analyzed. This study not only determined the primary reason for the atypical IBD epidemic, but also remind us of the urgency for developing new vaccines against novel variant IBDV.

Comparative in vivo pathogenicity study of an ITA genotype isolate (G6) of infectious bursal disease virus.

Recently, a new genotype of infectious bursal disease virus (IBDV), named ITA, was detected in IBD-vaccinated Italian broilers. Genome characterization revealed ITA to be a genetically different IBDV, belonging to genogroup 6 according to a recently proposed IBDV classification. The currently available clinical data do not allow any definition of the degree of pathogenicity of the ITA-IBDV isolates. In the present study, a pathogenicity trial was conducted by the oral inoculation of specific-pathogen-free (SPF) chickens. Birds were housed in poultry isolators and inoculated at 35 days of age with an ITA-IBDV isolate (35 birds) or a strain belonging to the G1a genogroup as a comparison (35 birds). Control birds (25 birds) were contextually mock-inoculated with sterile water. Birds were observed daily for clinical signs and at 0, 7, 14, 21 and 28 days post-inoculation (dpi) were bled for IBDV antibody detection. At 2, 4, 7, 14, 21 and 28 dpi, five birds from each of the inoculated groups, and three from the control group, were euthanized and subjected to a post-mortem examination; the bursa:body weight and thymus:body weight ratios were calculated. Microscopic lesions of the bursa and thymus were scored on the basis of lymphoid necrosis and/or depletion or cortex atrophy, respectively. Both viruses induced a subclinical course of disease, as neither clinical signs nor mortality were recorded during the study, even in the presence of typical IBDV gross and microscopic lesions. Bursal damage, measured by the bursa:body weight ratio, was more noticeable and precocious after ITA-IBDV inoculation. Histopathology scores of the bursa, indicative of rapid lymphoid depletion, confirmed the aggressiveness of the ITA-IBDV strain in this organ. This study showed that, although the ITA-IBDV strain tested causes infection with a subclinical course, it induces severe damage to lymphoid tissues. Therefore, its circulation in birds might be a threat for the poultry industry and may jeopardize the success of the production cycle.

Differential expression of immune-related genes in the bursa of Fabricius of two inbred chicken lines following infection with very virulent infectious bursal disease virus.

Among different inbred chickens' lines, we previously showed that lines P and N of Institute for Animal Health, Compton, UK are the most susceptible and the least affected lines, respectively, following infection with very virulent infectious bursal disease virus (vvIBDV). In this study, the differential expressions of 29 different immune-related genes were characterized. Although, birds from both lines succumbed to infection, line P showed greater bursal lesion scores and higher viral copy numbers compared to line N. Interestingly, line N showed greater down-regulation of B cell related genes (BLNK, TNFSF13B and CD72) compared to line P. While up-regulation of T-cell related genes (CD86 and CTLA4) and Th1 associated cytokines (IFNG, IL2, IL12A and IL15) were documented in both lines, the expression levels of these genes were different in the two lines. Meanwhile, the expression of IFN-related genes IFNB, STAT1, and IRF10, but not IRF5, were up-regulated in both lines. The expression of pro-inflammatory cytokines (IL1B, IL6, IL18, and IL17) and chemokines (CXCLi2, CCL4, CCL5 and CCR5) were up-regulated in both lines with greater increase documented in line P compared to line N. Strikingly, the expression of IL12B was detected only in line P whilst the expression of IL15RA was detected only in line N. In conclusion, the bursal immunopathology of IBDV correlates more with expression of proinflammatory response related genes and does not related to expression of B-cell related genes.

Phylogenetic analyses and pathogenicity of a variant infectious bursal disease virus strain isolated in China.

Infectious bursal disease is an acute, highly contagious, immunosuppressive disease of young chickens caused by infectious bursal disease virus (IBDV). In recent years, there has been a notable increase in the isolation rates of variant IBDV strains in China; however, the pathogenicity of these variants is unclear. In the current study, we characterized variant IBDV strain ZD-2018-1 and assessed its pathogenicity in specific-pathogen-free chickens. Phylogenetic analysis revealed that ZD-2018-1 belonged to the variant IBDV strain, which showed several unique amino acid mutations compared with other previously-isolated variant IBDV strains. Pathogenicity assays showed that ZD-2018-1 was less virulent than very virulent IBDV strain SD-2013-1, and did not cause an obvious symptoms or death. In comparison, strain SD-2013-1 had a high mortality rate and caused severe lesions in various tissues. However, both of the strains induced obvious pathological lesions on the bursa of Fabricius, resulting in severe immunosuppression in the infected chickens. The results of this study present a systematic evaluation of the genetic characteristics, pathogenicity, and immunosuppressive properties of a new variant IBDV strain, and may help in the development of strategies for the prevention and control of IBDV in poultry.

Newcastle Disease Virus Nonstructural V Protein Upregulates SOCS3 Expression to Facilitate Viral Replication Depending on the MEK/ERK Pathway.

Newcastle disease virus (NDV) causes serious economic losses to the poultry industry. In our previous study, we found that NDV induced a strong innate immune response in the chicken embryo and bursa of Fabricius (BF). However, the underlying mechanisms by which NDV escapes the host innate immunity are not well-understood. The suppressor of cytokine signaling 3 (SOCS3) inhibits the type I interferon-dependent antiviral signaling pathway by utilizing a feedback loop. In this study, we analyzed the transcriptome data of the chicken embryo and BF infected with NDV and found significant upregulation of SOCS3. Next, we demonstrated that NDV infection and nonstructural V protein induced the up-regulation of SOCS3. Furthermore, we showed that overexpression of SOCS3 facilitated viral replication and reduced the expression of phosphorylation STAT1, MX1, and OASL, while inhibition of SOCS3 with siRNAs reduced virus replication and promoted the expression of phosphorylation STAT1, MX1, and OASL. Finally, we demonstrated that the MEK/ERK signaling pathway was involved in the expression of SOCS3 mediated by NDV infection and V protein transfection, and using specific inhibitor U0126 to block this signaling pathway attenuated SOCS3 expression and inhibited NDV replication through promoting the expression of type I interferon, OASL and MX1. Taken together, these data demonstrate that NDV infection and NDV nonstructural V protein activates the expression of SOCS3 at the mRNA and protein level through a mechanism dependent on the MEK/ERK signaling pathway, which benefits virus replication.

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.