Cross-reactive, cell-mediated immunity and protection of chickens from lethal H5N1 influenza virus infection in Hong Kong poultry markets

Chicken TCRγδ+CD8α+T cells are antigen-specific and protective in H9N2 AIV infection

TCRγδ+ T cells are a major lymphocyte population of chickens, but their response or contribution to immunity against avian influenza virus (AIV) remains unknown. Here, we report an increase in the proportion and activation state of TCRγδ+CD8α+ T cells in the PBMCs of 3 chicken lines (MHC homozygous H-B2 and H-B21 lines and outbred G-WL line) with the strongest responses observed in the more resistant H-B2 chickens. H9N2 AIV infection induced mRNA upregulation of interferon (IFN)-γ and cytotoxicity-associated molecules, including, Granzyme A, Granzyme K, and perforin in sorted TCRγδ+CD8α+ T cells. Moreover, in ex vivo cultured TCRγδ+CD8α+ T cells in response to H9N2 AIV infected splenocytes, strongly indicates the activation of these cells' cytolytic potential via detection of transcription levels of cytotoxic genes with quantitative reverse transcription polymerase chain reaction (qRT-PCR), and IFN-γ protein level with ELISPOT and an intracellular cytokine staining assays. Most importantly, in vivo depletion of γδ T cells led to reduced H9N2 AIV control, which was particularly evident in the early phase of infection. Taken together, these results indicate that strong TCRγδ+CD8α+T cell response plays a critical role in protecting chicken against H9N2 AIV infection.

Immune responses to avian influenza viruses in chickens

Chickens are a key species in both the manifestation of avian influenza and the potential for zoonotic transmission. Avian influenza virus (AIV) infection in chickens can range from asymptomatic or mild disease with low pathogenic AIVs (LPAIVs) to systemic fatal disease with high pathogenic AIVs (HPAIVs). During AIV infection in chickens, Toll-like receptor 7 and melanoma differentiation-associated gene 5 are upregulated to detect the single-stranded ribonucleic acid genomes of AIV, triggering a signaling cascade that produces interferons (IFNs) and pro-inflammatory cytokines. These inflammatory mediators induce the expression of antiviral proteins and recruit immune system cells, such as macrophages and dendritic cells, to the infection site. AIV evades these antiviral responses primarily through its non-structural protein 1, which suppresses type I IFNs, influencing viral pathogenicity. The uncontrolled release of pro-inflammatory cytokines may contribute to the pathogenicity and high mortality associated with HPAIV infections. AIV modulates apoptosis in chicken cells to enhance its replication, with variations in apoptosis pathways influenced by viral strain and host cell type. The presentation of AIV antigens to T and B cells leads to the production of neutralizing antibodies and the targeted destruction of infected cells by CD8+ T cells, respectively, which enhances protection and establishes immunological memory. This review explores the diverse innate and adaptive immune responses in chickens to different AIVs, focusing on the dynamics of these responses relative to protection, susceptibility, and potential immunopathology. By understanding these immune mechanisms, informed strategies for controlling AIV infection and improving chicken health can be developed.

Broadly cross-reactive immune responses in chickens immunized with chimeric virus-like particles of nodavirus displaying the M2e originated from avian and human influenza A viruses

Avian influenza A viruses (IAVs) pose a persistent threat to poultry industry worldwide, despite the presence of vaccines. Additionally, reverse-zoonosis transmission potentially introduces human-originated IAVs into poultry and complicates the efforts to control the spread of influenza. Current avian influenza vaccines are primarily based upon the rapidly mutating hemagglutinin (HA) and neuraminidase (NA) glycoproteins, which limit their efficacy against diverse strains of IAVs. Hence, the highly conserved ectodomains of matrix 2 protein (M2e) of IAVs are widely studied as alternatives to the HA and NA. However, the differences in the M2e amino acid sequences between avian and human IAVs generate antibodies that do not cross-react reciprocally with IAVs from other origins. To broaden and enhance the immunogenicity of M2e, we fused two copies each of the M2e derived from avian and human IAVs at the C-terminal end of the Macrobrachium rosenbergii nodavirus (MrNV) capsid protein (NvC). Transmission electron microscopic and dynamic light scattering analyses revealed that the chimeric protein self-assembled into virus-like particles (VLPs). Immunization of chickens with the chimeric VLPs demonstrated a robust induction of broadly reactive immune responses against both the M2e of avian and human IAVs. Additionally, the chimeric VLPs elicited the production of cytotoxic T lymphocytes (CTL), macrophages, as well as a well-balanced Th1 and Th2 population, indicating their potential in activating cell-mediated immune responses in chickens. Furthermore, the chimeric VLPs triggered the production of both Th1- and Th2-cytokines, attesting their potential in mounting a robust and balanced immune response in avian species. This study demonstrated the potential of these chimeric VLPs in stimulating and broadening cross-reactive immune responses in chickens against both avian and human IAVs.

Evolutionary diversity of CXCL16-CXCR6: Convergent substitutions and recurrent gene loss in sauropsids

The CXCL16-CXCR6 axis is crucial for regulating the persistence of CD8 tissue-resident memory T cells (TRM). CXCR6 deficiency lowers TRM cell numbers in the lungs and depletes ILC3s in the lamina propria, impairing mucosal defence. This axis is linked to diseases like HIV/SIV, cancer, and COVID-19. Together, these highlight that the CXCL16-CXCR6 axis is pivotal in host immunity. Previous studies of the CXCL16-CXCR6 axis found genetic variation among species but were limited to primates and rodents. To understand the evolution and diversity of CXCL16-CXCR6 across vertebrates, we compared approximately 400 1-to-1 CXCR6 orthologs spanning diverse vertebrates. The unique DRF motif of CXCR6 facilitates leukocyte adhesion by interacting with cell surface-expressed CXCL16 and plays a key role in G-protein selectivity during receptor signalling; however, our findings show that this motif is not universal. The DRF motif is restricted to mammals, turtles, and frogs, while the DRY motif, typical in other CKRs, is found in snakes and lizards. Most birds exhibit the DRL motif. These substitutions at the DRF motif affect the receptor-Gi/o protein interaction. We establish recurrent CXCR6 gene loss in 10 out of 36 bird orders, including Galliformes and Passeriformes, Crocodilia, and Elapidae, attributed to segmental deletions and/or frame-disrupting changes. Notably, single-cell RNA sequencing of the lung shows a drop in TRM cells in species with CXCR6 loss, suggesting a possible link. The concurrent loss of ITGAE, CXCL16, and CXCR6 in chickens may have altered CD8 TRM cell abundance, with implications for immunity against viral diseases and vaccines inducing CD8 TRM cells.

Amplification of avian influenza virus circulation along poultry marketing chains in Bangladesh: A controlled field experiment

The prevalence of avian influenza viruses is commonly found to increase dramatically as birds are transported from farms to live bird markets. Viral transmission dynamics along marketing chains are, however, poorly understood. To address this gap, we implemented a controlled field experiment altering chicken supply to a live bird market in Chattogram, Bangladesh. Broilers and backyard chickens traded along altered (intervention) and conventional (control) marketing chains were tested for avian influenza viruses at different time points. Upon arrival at the live bird market, the odds of detecting avian influenza viruses did not differ between control and intervention groups. However, 12 h later, intervention group odds were lower, particularly for broilers, indicating that viral shedding in live bird markets resulted partly from infections occurring during transport and trade. Curtailing avian influenza virus prevalence in live bird markets requires mitigating risk in marketing chain nodes preceding chickens' delivery at live bird markets.

Revealing novel and conservative T-cell epitopes with MHC B2 restriction on H9N2 avian influenza virus (AIV)

B2 haplotype major histocompatibility complex (MHC) has been extensively reported to confer resistance to various avian diseases. But its peptide-binding motif is unknown, and the presenting peptide is rarely identified. Here, we identified its peptide-binding motif (X-A/V/I/L/P/S/G-X-X-X-X-X-X-V/I/L) in vitro using Random Peptide Library-based MHC I LC-MS/MS analysis. To further clarify the structure basis of motif, we determined the crystal structure of the BF2∗02:01-PB2552-560 complex at 1.9 Å resolution. We found that BF2∗02:01 had a relatively wide antigen-binding groove, and the structural characterization of pockets was consistent with the characterization of peptide-binding motif. The wider features of the peptide-binding motif and increased number of peptides bound by BF2∗02:01 than BF2∗04:01 might resolve the puzzles for the presence of potential H9N2 resistance in B2 chickens. Afterward, we explored the H9N2 avian influenza virus (AIV)-induced cellular immune response in B2 haplotype chickens in vivo. We found that ratio of CD8+ T cell and kinetic expression of cytotoxicity genes including Granzyme K, interferon-γ, NK lysin, and poly-(ADP-ribose) polymerase in peripheral blood mononuclear cells were significantly increased in defending against H9N2 AIV infection. Especially, we selected 425 epitopes as candidate epitopes based on the peptide-binding motif and further identified four CD8+ T-cell epitopes on H9N2 AIV including NS198-106, PB2552-560, NP182-190, and NP455-463 via ELI-spot interferon-γ detections after stimulating memory lymphocytes with peptides. More importantly, these epitopes were found to be conserved in H7N9 AIV and H9N2 AIV. These findings provide direction for developing effective T cell epitope vaccines using well-conserved internal viral antigens in chickens.

EPINEST, an agent-based model to simulate epidemic dynamics in large-scale poultry production and distribution networks

The rapid intensification of poultry production raises important concerns about the associated risks of zoonotic infections. Here, we introduce EPINEST (EPIdemic NEtwork Simulation in poultry Transportation systems): an agent-based modelling framework designed to simulate pathogen transmission within realistic poultry production and distribution networks. We provide example applications to broiler production in Bangladesh, but the modular structure of the model allows for easy parameterization to suit specific countries and system configurations. Moreover, the framework enables the replication of a wide range of eco-epidemiological scenarios by incorporating diverse pathogen life-history traits, modes of transmission and interactions between multiple strains and/or pathogens. EPINEST was developed in the context of an interdisciplinary multi-centre study conducted in Bangladesh, India, Vietnam and Sri Lanka, and will facilitate the investigation of the spreading patterns of various health hazards such as avian influenza, Campylobacter, Salmonella and antimicrobial resistance in these countries. Furthermore, this modelling framework holds potential for broader application in veterinary epidemiology and One Health research, extending its relevance beyond poultry to encompass other livestock species and disease systems.

Markets as drivers of selection for highly virulent poultry pathogens

Theoretical models have successfully predicted the evolution of poultry pathogen virulence in industrialized farm contexts of broiler chicken populations. Whether there are ecological factors specific to more traditional rural farming that affect virulence is an open question. Within non-industrialized farming networks, live bird markets are known to be hotspots of transmission, but whether they could shift selection pressures on the evolution of poultry pathogen virulence has not been addressed. Here, we revisit predictions for the evolution of virulence for viral poultry pathogens, such as Newcastle's disease virus, Marek's disease virus, and influenza virus, H5N1, using a compartmental model that represents transmission in rural markets. We show that both the higher turnover rate and higher environmental persistence in markets relative to farms could select for higher optimal virulence strategies. In contrast to theoretical results modeling industrialized poultry farms, we find that cleaning could also select for decreased virulence in the live poultry market setting. Additionally, we predict that more virulent strategies selected in markets could circulate solely within poultry located in markets. Thus, we recommend the close monitoring of markets not only as hotspots of transmission, but as potential sources of more virulent strains of poultry pathogens.

Emergence of a new genotype of clade 2.3.4.4b H5N1 highly pathogenic avian influenza A viruses in Bangladesh

Influenza virological surveillance was conducted in Bangladesh from January to December 2021 in live poultry markets (LPMs) and in Tanguar Haor, a wetland region where domestic ducks have frequent contact with migratory birds. The predominant viruses circulating in LPMs were low pathogenic avian influenza (LPAI) H9N2 and clade 2.3.2.1a highly pathogenic avian influenza (HPAI) H5N1 viruses. Additional LPAIs were found in both LPM (H4N6) and Tanguar Haor wetlands (H7N7). Genetic analyses of these LPAIs strongly suggested long-distance movement of viruses along the Central Asian migratory bird flyway. We also detected a novel clade 2.3.4.4b H5N1 virus from ducks in free-range farms in Tanguar Haor that was similar to viruses first detected in October 2020 in The Netherlands but with a different PB2. Identification of clade 2.3.4.4b HPAI H5N1 viruses in Tanguar Haor provides continued support of the role of migratory birds in transboundary movement of influenza A viruses (IAV), including HPAI viruses. Domestic ducks in free range farm in wetland areas, like Tangua Haor, serve as a conduit for the introduction of LPAI and HPAI viruses into Bangladesh. Clade 2.3.4.4b viruses have dominated in many regions of the world since mid-2021, and it remains to be seen if these viruses will replace the endemic clade 2.3.2.1a H5N1 viruses in Bangladesh.

Cationic Nanoparticle-Stabilized Vaccine Delivery System for the H9N2 Vaccine to Promote Immune Response in Chickens

Chinese yam polysaccharides (CYPs) have received wide attention for their immunomodulatory activity. Our previous studies had discovered that the Chinese yam polysaccharide PLGA-stabilized Pickering emulsion (CYP-PPAS) can serve as an efficient adjuvant to trigger powerful humoral and cellular immunity. Recently, positively charged nano-adjuvants are easily taken up by antigen-presenting cells, potentially resulting in lysosomal escape, the promotion of antigen cross-presentation, and the induction of CD8 T-cell response. However, reports on the practical application of cationic Pickering emulsions as adjuvants are very limited. Considering the economic damage and public-health risks caused by the H9N2 influenza virus, it is urgent to develop an effective adjuvant for boosting humoral and cellular immunity against influenza virus infection. Here, we applied polyethyleneimine-modified Chinese yam polysaccharide PLGA nanoparticles as particle stabilizers and squalene as the oil core to fabricate a positively charged nanoparticle-stabilized Pickering emulsion adjuvant system (PEI-CYP-PPAS). The cationic Pickering emulsion of PEI-CYP-PPAS was utilized as an adjuvant for the H9N2 Avian influenza vaccine, and the adjuvant activity was compared with the Pickering emulsion of CYP-PPAS and the commercial adjuvant (aluminum adjuvant). The PEI-CYP-PPAS, with a size of about 1164.66 nm and a ζ potential of 33.23 mV, could increase the H9N2 antigen loading efficiency by 83.99%. After vaccination with Pickering emulsions based on H9N2 vaccines, PEI-CYP-PPAS generated higher HI titers and stronger IgG antibodies than CYP-PPAS and Alum and increased the immune organ index of the spleen and bursa of Fabricius without immune organ injury. Moreover, treatment with PEI-CYP-PPAS/H9N2 induced CD4⁺ and CD8⁺ T-cell activation, a high lymphocyte proliferation index, and increased cytokine expression of IL-4, IL-6, and IFN-γ. Thus, compared with the CYP-PPAS and aluminum adjuvant, the cationic nanoparticle-stabilized vaccine delivery system of PEI-CYP-PPAS was an effective adjuvant for H9N2 vaccination to elicit powerful humoral and cellular immune responses.

Duck CD8+ T Cell Response to H5N1 Highly Pathogenic Avian Influenza Virus Infection In Vivo and In Vitro

Domestic ducks are the important host for H5N1 highly pathogenic avian influenza virus (HPAIV) infection and epidemiology, but little is known about the duck T cell response to H5N1 AIV infection. In infection experiments of mallard ducks, we detected significantly increased CD8+ cells and augmented expression of cytotoxicity-associated genes, including granzyme A and IFN-γ, in PBMCs from 5 to 9 d postinfection when the virus shedding was clearly decreased, which suggested the importance of the duck cytotoxic T cell response in eliminating H5N1 infection in vivo. Intriguingly, we found that a CD8high+ population of PBMCs was clearly upregulated in infected ducks from 7 to 9 d postinfection compared with uninfected ducks. Next, we used Smart-Seq2 technology to investigate the heterogeneity and transcriptional differences of the duck CD8+ cells. Thus, CD8high+ cells were likely to be more responsive to H5N1 AIV infection, based on the high level of expression of genes involved in T cell responses, activation, and proliferation, including MALT1, ITK, LCK, CD3E, CD247, CFLAR, IL-18R1, and IL-18RAP. More importantly, we have also successfully cultured H5N1 AIV-specific duck T cells in vitro, to our knowledge, for the first time, and demonstrated that the CD8high+ population was increased with the duck T cell activation and response in vitro, which was consistent with results in vivo. Thus, the duck CD8high+ cells represent a potentially effective immune response to H5N1 AIV infection in vivo and in vitro. These findings provide novel insights and direction for developing effective H5N1 AIV vaccines.

Infectious bursal disease virus replication is inhibited by avain T cell chemoattractant chemokine CCL19

Chemokine CCL19, together with its receptor CCR7, is one of the most important factors recruiting immune cells into target organ during virus infection. Our previous study has shown that CCL19 played a vital role in the process of T cell trafficking into bursae during bursal disease virus (IBDV) infection. In this study, we hypothesized that CCL19 could exert direct influences on IBDV replication other than recruiting immune cells. A eukaryotic expression vector of pEGFP-N1/CCL19 was successfully constructed and identified by PCR, double enzymes digestion, and sequencing. Different concentrations of pEGFP-N1/CCL19 plasmids were transfected into DF1 cells and CCL19 protein was highly expressed. Then, DF1 cells were infected with IBDV B87 strain post-transfection. Based on PCR and Western blot results, CCL19 could obviously decrease the gene levels of VP1 and VP2 and the protein levels of VP2 and VP3. When CCL19 was knocked down, the gene levels of VP1 and VP2 were significantly upregulated. Moreover, indirect immunostaining revealed that the IBDV content was largely decreased after CCL19 overexpression. Additionally, CCL19 inhibitory effects might rely on activation of the JNK signal pathway. Taken together, chemokine CCL19 directly blocks IBDV replication in DF1 cells, indicating that CCL19 could play crucial functions other than recruiting T cells during the pathogenesis of IBDV.

Evolutionary pressures rendered by animal husbandry practices for avian influenza viruses to adapt to humans

Commercial poultry operations produce and crowd billions of birds every year, which is a source of inexpensive animal protein. Commercial poultry is intensely bred for desirable production traits, and currently presents very low variability at the major histocompatibility complex. This situation dampens the advantages conferred by the MHC’s high genetic variability, and crowding generates immunosuppressive stress. We address the proteins of influenza A viruses directly and indirectly involved in host specificities. We discuss how mutants with increased virulence and/or altered host specificity may arise if few class I alleles are the sole selective pressure on avian viruses circulating in immunocompromised poultry. This hypothesis is testable with peptidomics of MHC ligands. Breeding strategies for commercial poultry can easily and inexpensively include high variability of MHC as a trait of interest, to help save billions of dollars as a disease burden caused by influenza and decrease the risk of selecting highly virulent strains.

The Evaluation of Cellular Immunity to Avian Viral Diseases: Methods, Applications, and Challenges

Cellular immune responses play critical roles in the control of viral infection. However, the immune protection against avian viral diseases (AVDs), a major challenge to poultry industry, is yet mainly evaluated by measuring humoral immune response though antibody-independent immune protection was increasingly evident in the development of vaccines against some of these diseases. The evaluation of cellular immune response to avian viral infection has long been neglected due to limited reagents and methods. Recently, with the availability of more immunological reagents and validated approaches, the evaluation of cellular immunity has become feasible and necessary for AVD. Herein, we reviewed the methods used for evaluating T cell immunity in chickens following infection or vaccination, which are involved in the definition of different cellular subset, the analysis of T cell activation, proliferation and cytokine secretion, and in vitro culture of antigen-presenting cells (APC) and T cells. The pros and cons of each method were discussed, and potential future directions to enhance the studies of avian cellular immunity were suggested. The methodological improvement and standardization in analyzing cellular immune response in birds after viral infection or vaccination would facilitate the dissection of mechanism of immune protection and the development of novel vaccines and therapeutics against AVD.

Prior infection with antigenically heterologous low pathogenic avian influenza viruses interferes with the lethality of the H5 highly pathogenic strain in domestic ducks

Low and highly pathogenic avian influenza viruses (LPAIVs and HPAIVs, respectively) have been co-circulating in poultry populations in Asian, Middle Eastern, and African countries. In our avian-flu surveillance in Vietnamese domestic ducks, viral genes of LPAIV and HPAIV have been frequently detected in the same individual. To assess the influence of LPAIV on the pathogenicity of H5 HPAIV in domestic ducks, an experimental co-infection study was performed. One-week-old domestic ducks were inoculated intranasally and orally with PBS (control) or 10⁶ EID₅₀ of LPAIVs (A/duck/Vietnam/LBM678/2014 (H6N6) or A/Muscovy duck/Vietnam/LBM694/2014 (H9N2)). Seven days later, these ducks were inoculated with HPAIV (A/Muscovy duck/Vietnam/LBM808/2015 (H5N6)) in the same manner. The respective survival rates were 100% and 50% in ducks pre-infected with LBM694 or LBM678 strains and both higher than the survival of the control group (25%). The virus titers in oral/cloacal swabs of each LPAIV pre-inoculation group were significantly lower at 3-5 days post-HPAIV inoculation. Notably, almost no virus was detected in swabs from surviving individuals of the LBM678 pre-inoculation group. Antigenic cross-reactivity among the viruses was not observed in the neutralization test. These results suggest that pre-infection with LPAIV attenuates the pathogenicity of HPAIV in domestic ducks, which might be explained by innate and/or cell-mediated immunity induced by the initial infection with LPAIV.

Single oral immunization of an attenuated Salmonella Gallinarium formulation consisting of equal quantities of strains secreting H9N2 hemagglutinin-HA1, HA2, and M2eCD154 induces significant protection against H9N2 and partial protection against Salmonella Gallinarium challenge in chickens

The present investigation describes a formulation of a live attenuated Salmonella Gallinarium (SG) vaccine candidate against H9N2 influenza and SG infections in chickens. The formulation consists of an equal ratio of three strains, JOL2158, JOL2113, and JOL2074, which deliver hemagglutinin; HA1, HA2, and matrix protein 2 (M2e):: CD154 fusion (M2eCD154) antigens designed for broad protection against the field-matched H9N2 serotypes. The vaccine was completely safe at the average inoculation doses of 10⁸ and 10⁹ CFU/bird/0.2 mL in phosphate-buffered saline (PBS) used in the study. Bird immunization as a single oral inoculation could significantly engage humoral IgG, mucosal IgA, and cell-mediated immune responses against each immunized antigen, compared to the PBS control group (P < 0.05). The immunological correlates were comparable with the level of protection derived against the H9N2 and SG challenge, which resulted in significant protection against the H9N2 but only partial protection against the SG challenge as we compared against the PBS control group. The level of protection against H9N2 was investigated by determining the viral copy number and histopathological assessment of lung tissues. The results indicated a significant reduction in viral activity and recovery of lung inflammation towards the 14th-day post-challenge in a dose-dependent manner. Upon SG challenge, birds in the PBS control group experienced 100 % mortality, while 40 % and 70 % protection was observed in the SG-immunized groups for each respective dose of inoculation. The present SG-mediated immunization strategy proposes a rapid and reliable vaccine development process that can be effectively used against influenza strains such as H9N2 and holds the potential to minimize fowl typhoid caused by SG strains, mitigating two economically important diseases in the poultry industry.

Flow Cytometric Evaluation of CD4+ and CD8+ T-cell Immune Response in SPF Chickens Induced by Fowlpox Vaccine

Fowlpox (FP) is a viral disease that is widely distributed throughout the world. The disease has an economic impact on the poultry industry, and its prevalence has even been reported in vaccinated flocks. The present study used flow cytometry to evaluate the CD4⁺ and CD8⁺ T-cell immune response of chicks induced by FP vaccine. 120 specific pathogen-free (SPF) 21-day-old chicks were randomly divided into three groups of 40. One group was used as negative control with PBS inoculation, the other two groups were inoculated with the local fowlpox vaccine produced by Razi Institute and commercial FP vaccines, and they were kept for five weeks. Peripheral blood mononuclear cells (PBMC) were isolated using Ficoll-Hypaque density gradients and the percentages of CD3⁺, CD3⁺, CD4⁺, and CD3⁺CD8⁺ T lymphocytes were analyzed with flow cytometry. Seven days post-immunization, a maximum (90-100%) swelling formation ("take") on the vaccination site was observed. The ratios of CD4⁺ to CD8⁺ T-lymphocytes in both vaccinated groups were significantly higher (p < 0.05) than the control group inoculated with PBS. The percentages of CD3⁺, CD3⁺CD4⁺, and CD3⁺CD8⁺ T-lymphocytes were increased in chickens vaccinated with commercial and local FP vaccines. There were no significant differences between the groups receiving commercial and local fowl pox vaccines. The present study showed that protective immunity could be associated with increased cellular immune responses, which has been interpreted as enhancing T-cell proliferation and increasing CD4⁺ to CD8⁺ ratios through vaccination with the FP vaccine. This study further suggests that the induction of enhanced immune responses is due mainly to the Th1-type response.

Surveillance on respiratory diseases reveals enzootic circulation of both H5 and H9 avian influenza viruses in small-scale commercial layer farms of Bangladesh

Poultry production in Bangladesh has been experiencing H5N1 highly pathogenic avian influenza (HPAI) and H9N2 low pathogenic avian influenza (LPAI) for the last 14 years. Vaccination of chickens against H5 HPAI is in practice since the end of 2012. Subsequently, the official reporting of HPAI outbreaks gradually decreased. However, the true extent of circulation of avian influenza virus (AIV) in commercial poultry production is not clear. To explore this, we conducted active surveillance in 422 small-scale commercial layer farms in 20 villages of Mymensingh and Tangail districts of Bangladesh during 2017 and 2018 for the presence of diseases with respiratory signs. A total of 88 farms with respiratory disease problems were identified and investigated during the surveillance. In addition, 22 small-scale commercial layer farms in the neighbouring areas with respiratory disease problem were also investigated on request from the farmers. Pooled samples of oropharyngeal swabs from live birds or respiratory tissues from dead birds of the farm suffering from respiratory disease problem were tested for molecular detection of avian influenza virus (AIV), Newcastle disease virus (NDV), infectious bronchitis virus (IBV), infectious laryngotracheitis virus (ILTV), Mycoplasma gallisepticum and Avibacterium paragallinarum. A total of 110 farms (88 in the surveillance site and 22 in the neighbouring region) were investigated, and one or more respiratory pathogens were detected from 89 farms. AIV was detected in 57 farms often concurrently with other pathogens. Among these 57 farms, H5, H9, both H5 and H9 or non-H5 and non-H9 AIV were detected in 28, 9, 13 or 7 farms, respectively. Birds of most of the H5 AIV-positive farms did not present typical clinical signs or high mortality. Twenty such farms were observed longitudinally, which had only 1.05%-5.50% mortality but a marked drop in egg production. This widespread circulation of H5 AIV along with H9 AIV and other pathogens in small-scale commercial layer farms, often with low mortality, reaffirms the enzootic circulation of AIV in Bangladesh, which may escape syndromic surveillance focused on unusual mortality only. To reduce public health risks, strengthening of the control programme with comprehensive vaccination, enhanced biosecurity, improved surveillance and outbreak response is suggested.

A quantitative risk assessment to evaluate the efficacy of mitigation strategies to reduce highly pathogenic avian influenza virus, subtype H5N1 (HPAI H5N1) in the Menoufia governorate, Egypt

BACKGROUND

The poultry industry in Egypt has been suffering from endemic highly pathogenic avian influenza (HPAI) virus, subtype H5N1 since 2006. However, the emergence of H9N2, H5N8, and H5N2 in 2011, 2016, and 2019 respectively, has aggravated the situation. Our objective was to evaluate how effective are the mitigation strategies by a Quantitative Risk Assessment (QRA) model which used daily outbreak data of HPAI-H5N1 subtype in Egypt, stratified by different successive epidemic waves from 2006 to 2016.

RESULTS

By applying the epidemiologic problem-oriented approach methodology, a conceptual scenario tree was drawn based on the knowledgebase. Monte Carlo simulations of QRA parameters based on outbreak data were performed using @Risk software based on a scenario-driven decision tree. In poultry farms, the expected probability of HPAI H5N1 prevalence is 48% due to failure of mitigation strategies in 90% of the time during Monte Carlo simulations. Failure of efficacy of these mitigations will raise prevalence to 70% with missed vaccination, while failure in detection by surveillance activities will raise it to 99%. In backyard poultry farms, the likelihood of still having a high HPAI-H5N1 prevalence in different poultry types due to failure of passive and active surveillance varies between domestic, mixed and reservoir. In mixed poultry, the probability of HPAI-H5N1 not detected by surveillance was the highest with a mean and a SD of 16.8 × 10-3 and 3.26 × 10-01 respectively. The sensitivity analysis ranking for the likelihood of HPAI-H5N1 in poultry farms due to missed vaccination, failure to be detected by passive and active surveillance was examined. Among poultry farms, increasing vaccination by 1 SD will decrease the prevalence by 14%, while active and passive surveillance decreases prevalence by 12, and 6%, respectively. In backyard, the active surveillance had high impact in decreasing the prevalence by 16% in domestic chicken. Whereas the passive surveillance had less impact in decreasing prevalence by 14% in mixed poultry and 3% in domestic chicken.

CONCLUSION

It could be concluded that the applied strategies were not effective in controlling the spread of the HPAI-H5N1 virus. Public health officials should take into consideration the evaluation of their control strategies in their response.

T cell mediated immunity against influenza H5N1 nucleoprotein, matrix and hemagglutinin derived epitopes in H5N1 survivors and non-H5N1 subjects

Background

Protection against the influenza virus by a specific antibody is relatively strain specific; meanwhile broader immunity may be conferred by cell-mediated immune response to the conserved epitopes across influenza virus subtypes. A universal broad-spectrum influenza vaccine which confronts not only seasonal influenza virus, but also avian influenza H5N1 virus is promising.

Methods

This study determined the specific and cross-reactive T cell responses against the highly pathogenic avian influenza A (H5N1) virus in four survivors and 33 non-H5N1 subjects including 10 H3N2 patients and 23 healthy individuals. Ex vivo IFN-γ ELISpot assay using overlapping peptides spanning the entire nucleoprotein (NP), matrix (M) and hemagglutinin (HA) derived from A/Thailand/1(KAN-1)/2004 (H5N1) virus was employed in adjunct with flow cytometry for determining T cell functions. Microneutralization (microNT) assay was performed to determine the status of previous H5N1 virus infection.

Results

IFN-γ ELISpot assay demonstrated that survivors nos. 1 and 2 had markedly higher T cell responses against H5N1 NP, M and HA epitopes than survivors nos. 3 and 4; and the magnitude of T cell responses against NP were higher than that of M and HA. Durability of the immunoreactivity persisted for as long as four years after disease onset. Upon stimulation by NP in IFN-γ ELISpot assay, 60% of H3N2 patients and 39% of healthy subjects exhibited a cross-reactive T cell response. The higher frequency and magnitude of responses in H3N2 patients may be due to blood collection at the convalescent phase of the patients. In H5N1 survivors, the effector peptide-specific T cells generated from bulk culture PBMCs by in vitro stimulation displayed a polyfunction by simultaneously producing IFN-γ and TNF-α, together with upregulation of CD107a in recognition of the target cells pulsed with peptide or infected with rVac-NP virus as investigated by flow cytometry.

Conclusions

This study provides an insight into the better understanding on the homosubtypic and heterosubtypic T cell-mediated immune responses in H5N1 survivors and non-H5N1 subjects. NP is an immunodominant target of cross-recognition owing to its high conservancy. Therefore, the development of vaccine targeting the conserved NP may be a novel strategy for influenza vaccine design.

Establishment of Adequate Functional Cellular Immune Response in Chicks Is Age Dependent

The development of immunocompetence in chicks after hatching is not fully understood. However, detailed knowledge of immunocompetence and maturation processes in day-old chicks (DOCs) and juvenile chickens (Gallus gallus domesticus) is necessary to implement enhanced immunization strategies. For viral diseases, this especially includes the development of cellular immunity focusing on T-cell-dependent responses. In the current study, we investigated T-cell subsets in blood and lymphoid tissues of 1-to-21-day-old chickens concerning their cellular composition and localization. We detected an increase of T-cell frequencies in blood and spleen and a shift of the CD8α dimer expression toward a CD8αβ expression on the surface of T cells with increasing age. A relocalization of lymphocytes into antigen presentation structures within the spleen was affirmed. In addition, changes in basal messenger RNA (mRNA) level, with increasing IL2 and IFNγ mRNA levels at different ages were measured. These detected changes suggest an improved T-cell-dependent antiviral response with increasing age in chickens. To confirm this finding on a functional level, we conducted a transfer experiment: adult and, as a negative control, neonatal naïve lymphocytes were transferred into DOCs. Afterward, the protection induced by these transferred cells was verified by a sublethal infection by using a highly pathogenic avian influenza virus with neuraminidase deletion, H5N_del. Previous experiments have shown that adult animals survive infection with this virus strain, while naïve DOCs show severe symptoms or even die. As a result, the transfer of adult, but not neonatal lymphocytes, confers protection to DOCs against the infection, demonstrating functional differences in lymphocytes from chicks of different ages. Collectively, these data reveal the inability of chicks to mount an effective, cellular antiviral response in the first 3 wk of life. Therefore, we propose that the observed maturation of both the innate and the adaptive arms of the immune system early in development is mandatory for controlling influenza infection in chickens, as well as for an effective vaccination with replication-competent viral vaccine strains.

Oral immunization with an attenuated Salmonella Gallinarum encoding the H9N2 haemagglutinin and M2 ectodomain induces protective immune responses against H9N2 infection in chickens

H9N2, a low pathogenic avian influenza virus, causes significant economic losses in the poultry industry worldwide. Herein, we describe the construction of an attenuated Salmonella Gallinarum (SG) strain for expression and delivery of H9N2 haemagglutinin (HA) 1 (SG-HA1), HA2 (SG-HA2) and/or the conserved matrix protein 2 ectodomain (SG-M2e). We demonstrated that recombinant SG strains expressing HA1, HA2 and M2e antigens were immunogenic and safe in a chicken model. Chickens (n = 8) were vaccinated once orally with SG alone, SG-HA1, SG-HA2, SG-M2e, or mixture of SG-HA1, SG-HA2 and SG-M2e, or vaccinated once intramuscularly with an oil-adjuvant inactivated H9N2 vaccine. Our results demonstrated that vaccination with SG mutants encoding influenza antigens, administered individually or as a mixture, elicited significantly (P < 0.05) greater antigen-specific humoral and cell-mediated immune responses in chickens compared with those vaccinated with SG alone. A conventional H9N2 vaccine induced significantly (P < 0.05) greater HA1 and HA2 antibody responses than SG-based H9N2 vaccine strains, but significantly (P < 0.05) less robust M2e-specific responses. Upon challenge with the virulent H9N2 virus on day 28 post-vaccination, chickens vaccinated with either the SG-based H9N2 or conventional H9N2 vaccines exhibited comparable lung inflammation and viral loads, although both were significantly lower (P < 0.05) than in the group vaccinated with SG alone. In conclusion, our results showed that SG-based vaccination stimulated efficient immune responses against virulent H9N2. Further studies are needed to fully develop this approach as a preventive strategy for low pathogenic avian influenza viruses affecting poultry. RESEARCH HIGHLIGHTS S. gallinarum expressing HA1, HA2 and M2e antigens are immunogenic and safe. Salmonella has dual function of acting as a delivery system and as a natural adjuvant. Vaccine constructs elicit specific humoral and cell-mediated immune responses.

Protection of layers and breeders against homologous or heterologous HPAIv by vaccines from Korean national antigen bank

Korean government has selected and stocked five type antigens of two clades as Korean national antigen bank having high possibility of introduction to Korea. We aimed to evaluate the efficacy of the clade 2.3.2.1c and 2.3.4.4c H5Nx vaccines from the Korean avian influenza (AI) national antigen bank for emergency preparedness for their potency and protective efficacy against lethal homologous and heterologous viruses in layer and breeder chickens practically. The PD₅₀ (dose of vaccine that protects 50% of chickens from viral challenge) of all vaccinated groups was >50, which was satisfied with minimum antigen requirement of OIE, and the PD₅₀ levels of the two vaccines differed depending on strain and chicken breed. In homologous challenge, all vaccinated groups exhibited 100% survival with no clinical symptoms and high levels of pre-challenge protective immunity (7.2–8.5 log₂), although they did not completely prevent virus shedding. On the other hand, against heterologous virus challenge, vaccinated animals exhibited 62.5–80% survival with lower antibody titers (2.3–3.4 log₂) and a longer period of virus shedding (14 days post infection [dpi]). Our results suggest that the clade 2.3.2.1c and 2.3.4.4c H5Nx vaccines are good candidates for emergency vaccination of commercial chickens and support the idea that close genetic matching between vaccine and challenge virus provides the best protection.

Non-sterilizing, Infection-Permissive Vaccination With Inactivated Influenza Virus Vaccine Reshapes Subsequent Virus Infection-Induced Protective Heterosubtypic Immunity From Cellular to Humoral Cross-Reactive Immune Responses

Conventional influenza vaccines aim at the induction of virus-neutralizing antibodies that provide with sterilizing immunity. However, influenza vaccination often confers protection from disease but not from infection. The impact of infection-permissive vaccination on the immune response elicited by subsequent influenza virus infection is not well-understood. Here, we investigated to what extent infection-permissive immunity, in contrast to virus-neutralizing immunity, provided by a trivalent inactivated virus vaccine (TIV) modulates disease and virus-induced host immune responses after sublethal vaccine-matching H1N1 infection in a mouse model. More than one TIV vaccination was needed to induce a serum HI titer and provide sterilizing immunity upon homologous virus infection. However, single TIV administration provided infection-permissive immunity, characterized by lower viral lung titers and faster recovery. Despite the presence of replicating virus, single TIV vaccination prevented induction of pro-inflammatory cyto- and chemokines, alveolar macrophage depletion as well as the establishment of lung-resident B and T cells after infection. To investigate virus infection-induced cross-protective heterosubtypic immune responses in vaccinated and unvaccinated animals, mice were re-infected with a lethal dose of H3N2 virus 4 weeks after H1N1 infection. Single TIV vaccination did not prevent H1N1 virus infection-induced heterosubtypic cross-protection, but shifted the mechanism of cross-protection from the cellular to the humoral branch of the immune system. These results suggest that suboptimal vaccination with conventional influenza vaccines may still positively modulate disease outcome after influenza virus infection, while promoting humoral heterosubtypic immunity after virus infection.

Structures of the MHC-I molecule BF2*1501 disclose the preferred presentation of an H5N1 virus-derived epitope

Lethal infections by strains of the highly-pathogenic avian influenza virus (HPAIV) H5N1 pose serious threats to both the poultry industry and public health worldwide. A lack of confirmed HPAIV epitopes recognized by cytotoxic T lymphocytes (CTLs) has hindered the utilization of CD8+ T-cell-mediated immunity and has precluded the development of effectively diversified epitope-based vaccination approaches. In particular, an HPAIV H5N1 CTL-recognized epitope based on the peptide MHC-I-β2m (pMHC-I) complex has not yet been designed. Here, screening a collection of selected peptides of several HPAIV strains against a specific pathogen-free pMHC-I (pBF2*1501), we identified a highly-conserved HPAIV H5N1 CTL epitope, named HPAIV-PA123-130 We determined the structure of the BF2*1501-PA123-130 complex at 2.1 Å resolution to elucidate the molecular mechanisms of a preferential presentation of the highly-conserved PA123-130 epitope in the chicken B15 lineage. Conformational characteristics of the PA123-130 epitope with a protruding Tyr-7 residue indicated that this epitope has great potential to be recognized by specific TCRs. Moreover, significantly increased numbers of CD8+ T cells specific for the HPAIV-PA123-130 epitope in peptide-immunized chickens indicated that a repertoire of CD8+ T cells can specifically respond to this epitope. We anticipate that the identification and structural characterization of the PA123-130 epitope reported here could enable further studies of CTL immunity against HPAIV H5N1. Such studies may aid in the development of vaccine development strategies using well-conserved internal viral antigens in chickens.

Techniques for the Measurement of Cell Mediated Immune Responses to Avian Influenza Virus

Cellular immune responses, through both T and B cells, are critical to understanding the role and regulation of lymphocytes following viral infection, as well as defining responses to vaccination. T cells play a critical role in adaptive immunity, including pathogen elimination through the engagement of CD4 and CD8 receptors, which trigger signaling mechanisms. B cells contribute to generating antibodies following exposure to foreign pathogens through interactions with CD4+ lymphocytes. While these different cell types have distinctly different modes of action in terms of contributions to protection (cytotoxic versus antibody mediated), they account for the majority of adaptive immunity induced following infection or vaccination. While the ability to measure cell-mediated immunity (CMI) has steadily improved, there is much to learn with regard to their contribution to the protection of birds against diseases induced by avian influenza virus. The rapidly increasing knowledge of genomic avian sequences, along with the increasing availability of monoclonal antibodies detecting avian cell-associated antigen markers, has made techniques to measure CMI more specific and informative for researchers.

Antiviral responses against chicken respiratory infections: Focus on avian influenza virus and infectious bronchitis virus

Some of the respiratory viral infections in chickens pose a significant threat to the poultry industry and public health. In response to viral infections, host innate responses provide the first line of defense against viruses, which often act even before the establishment of the infection. Host cells sense the presence of viral components through germinal encoded pattern recognition receptors (PRRs). The engagement of PRRs with pathogen-associated molecular patterns leads to the induction of pro-inflammatory and interferon productions. Induced antiviral responses play a critical role in the outcome of the infections. In order to improve current strategies for control of viral infections or to advance new strategies aimed against viral infections, a deep understanding of host-virus interaction and induction of antiviral responses is required. In this review, we summarized recent progress in understanding innate antiviral responses in chickens with a focus on the avian influenza virus and infectious bronchitis virus.

Prevalence and Phylogenetics of H9n2 in Backyard and Commercial Poultry in Pakistan

Surveillance of H9N2 is currently focused on areas central to the commercial poultry industry. This study determined the prevalence of H9N2 virus in commercial and backyard poultry flocks in Punjab Province, Pakistan. Oral and tracheal swabs were collected from commercial and backyard poultry from January 2015 through June 2016. Antisera against H5, H7, H9, and Newcastle disease viruses were used for virus identification. Molecular confirmation was made by reverse transcription PCR. Avian influenza virus subtypes H5 and H7 were not detected. The H9N2 virus was isolated in 5.7% of 905 tested flocks (5-10 birds/flock). Prevalence in commercial and backyard poultry was 6.7% of 687 flocks and 2.7% of 218 flocks, respectively. Hemagglutinin and neuraminidase-gene-based phylogenetic analysis of commercial and backyard poultry isolates showed 100% homology. Within sublineage B2 of Pakistan, identity among most recent isolates (2015) was 100%, compared to 75%-99% identity with previously isolated viruses (2010-12), indicating continued virus evolution. Most of the previously reported and currently studied viruses were isolated near the Pakistan-India border. Phylogenetic analysis showed that Pakistani and Indian isolates were closely related, indicating that avian influenza virus transmission may occur across this border.

Progress on chicken T cell immunity to viruses

Avian virus infection remains one of the most important threats to the poultry industry. Pathogens such as avian influenza virus (AIV), avian infectious bronchitis virus (IBV), and infectious bursal disease virus (IBDV) are normally controlled by antibodies specific for surface proteins and cellular immune responses. However, standard vaccines aimed at inducing neutralizing antibodies must be administered annually and can be rendered ineffective because immune-selective pressure results in the continuous mutation of viral surface proteins of different strains circulating from year to year. Chicken T cells have been shown to play a crucial role in fighting virus infection, offering lasting and cross-strain protection, and offer the potential for developing universal vaccines. This review provides an overview of our current knowledge of chicken T cell immunity to viruses. More importantly, we point out the limitations and barriers of current research and a potential direction for future studies.

Pathobiological features favouring the intercontinental dissemination of highly pathogenic avian influenza virus

Avian influenza viruses (AIVs) are a continued threat to global health and economy. Unlike other highly pathogenic AIVs, novel H5N8 disseminated very quickly from Korea to other areas in Asia, Europe and even North America following its first outbreak in 2014. However, the pathobiological features of the virus that favoured its global translocation remain unknown. In this study, we used a compartmental model to examine the avian epidemiological characteristics that would support the geographical spread of influenza by bird migration, and to provide recommendations for AIV surveillance in wild bird populations. We simulated virus transmission and translocation in a migratory bird population while varying four system properties: (i) contact transmission rate; (ii) infection recovery rate; (iii) mortality rate induced by infection; and (iv) migratory recovery rate. Using these simulations, we then calculated extinction and translocation probabilities for influenza during spring migration as a function of the altered properties. We find that lower infection recovery rates increase the likelihood of AIV translocation in migratory bird populations. In addition, lower mortality rates or migration recovery rates also favour translocation. Our results identify pathobiological features supporting AIV intercontinental dissemination risk and suggest that characteristic differences exist among H5N8 and other AIV subtypes that have not translocated as rapidly (e.g. H5N6 and H5N1).

A viral race for primacy: co-infection of a natural pair of low and highly pathogenic H7N7 avian influenza viruses in chickens and embryonated chicken eggs

Highly pathogenic avian influenza virus (HPAIV) infection in poultry caused devastating mortality and economic losses. HPAIV of subtypes H5 and H7 emerge from precursor viruses of low pathogenicity (LP) by spontaneous mutation associated with a shift in the susceptibility of the endoproteolytic cleavage site of the viral hemagglutinin protein from trypsin- to furin-like proteases. A recently described natural pair of LP/HP H7N7 viruses derived from two spatio-temporally linked outbreaks in layer chickens was used to study how a minority of mutated HP virions after de novo generation in a single host might gain primacy. Co-infection experiments in embryonated eggs and in chickens were conducted to investigate amplification, spread and transmissionof HPAIV within a poultry population that experiences concurrent infection by an antigenically identical LP precursor virus. Simultaneous LPAIV co-infection (inoculum dose of 106 egg-infectious dose 50% endpoint (EID50)/0.5 mL) withincreasing titers of HPAIV from 101 to 105.7 EID50/0.5 mL) had a significant impeding impact on HP H7 replication, viral excretion kinetics, clinical signs and histopathological lesions (in vivo) and on embryo mortality (in ovo). LP/HP co-infected chickens required a hundredfold higher virus dose (HPAIV inoculum of 105 EID50) compared to HPAIV mono-infection (HPAIV inoculum of 103 EID50) to develop overt clinical signs, mortality and virus spread to uninfected sentinels. Escape and spread of HP phenotypes after de novo generation in an index host may therefore be highly precarious due to significant competition with co-circulating LP precursor virus.

Influenza A Virus Negative Strand RNA Is Translated for CD8+ T Cell Immunosurveillance

Probing the limits of CD8⁺ T cell immunosurveillance, we inserted the SIINFEKL peptide into influenza A virus (IAV)-negative strand gene segments. Although IAV genomic RNA is considered noncoding, there is a conserved, relatively long open reading frame present in segment 8, encoding a potential protein termed NEG8. The biosynthesis of NEG8 from IAV has yet to be demonstrated. Although we failed to detect NEG8 protein expression in IAV-infected mouse cells, cell surface K^b-SIINFEKL complexes are generated when SIINFEKL is genetically appended to the predicted C terminus of NEG8, as shown by activation of OT-I T cells in vitro and in vivo. Moreover, recombinant IAV encoding of SIINFEKL embedded in the negative strand of the neuraminidase-stalk coding sequence also activates OT-I T cells in mice. Together, our findings demonstrate both the translation of sequences on the negative strand of a single-stranded RNA virus and its relevance in antiviral immunosurveillance.

A consensus-hemagglutinin-based vaccine delivered by an attenuated Salmonella mutant protects chickens against heterologous H7N1 influenza virus

H7N3 and H7N7 are highly pathogenic avian influenza (HPAI) viruses and have posed a great threat not only for the poultry industry but for the human health as well. H7N9, a low pathogenic avian influenza (LPAI) virus, is also highly pathogenic to humans, and there is a great concern that these H7 subtypes would acquire the ability to spread efficiently between humans, thereby becoming a pandemic threat. A vaccine candidate covering all the three subtypes must, therefore, be an integral part of any pandemic preparedness plan. To address this need, we constructed a consensus hemagglutinin (HA) sequence of H7N3, H7N7, and H7N9 based on the data available in the NCBI in early 2012-2015. This artificial sequence was then optimized for protein expression before being transformed into an attenuated auxotrophic mutant of Salmonella Typhimurium, JOL1863 strain. Immunizing chickens with JOL1863, delivered intramuscularly, nasally or orally, elicited efficient humoral and cell mediated immune responses, independently of the route of vaccination. Our results also showed that JOL1863 deliver efficient maturation signals to chicken monocyte derived dendritic cells (MoDCs) which were characterized by upregulation of costimulatory molecules and higher cytokine induction. Moreover, immunization with JOL1863 in chickens conferred a significant protection against the heterologous LPAI H7N1 virus challenge as indicated by reduced viral sheddings in the cloacal swabs. We conclude that this vaccine, based on a consensus HA, could induce broader spectrum of protection against divergent H7 influenza viruses and thus warrants further study.

Examination of the effects of virus inactivation methods on the induction of antibody- and cell-mediated immune responses against whole inactivated H9N2 avian influenza virus vaccines in chickens

Several types of avian influenza virus (AIV) vaccines exist, including live-attenuated, vectored, and whole inactivated virus (WIV) vaccines. Inactivated vaccines offer some advantages compared to other types of vaccines, including ease of production and lack of ability to revert to a virulent state. However, WIV are poorly immunogenic, especially when these vaccines are delivered to mucosal surfaces. There are several factors that contribute to the immunogenicity of vaccines, one of which is the method used to inactivate viruses. Several methods exist for producing influenza WIVs, including formaldehyde, a chemical that affects protein structures leading to virus inactivation. Other methods include treatment with beta-propiolactone (BPL) and the application of gamma radiation, both of which have less effects on protein structures compared to formaldehyde, and instead alter nucleic acids in the virion. Here, we sought to determine the effect of the above inactivation methods on immunogenicity of AIV vaccines. To this end, chickens were vaccinated with three different H9N2 WIVs using formaldehyde, BPL, and gamma radiation for inactivation. In addition to administering these three WIVs alone as vaccines, we also included CpG ODN 2007, a synthetic ligand recognized by Toll-like receptor (TLR)21 in chickens, as an adjuvant for each WIV. Subsequently, antibody- and cell-mediated immune responses were measured following vaccination. Antibody-mediated immune responses were increased in chickens that received the BPL and Gamma WIVs compared to the formaldehyde WIV. CpG ODN 2007 was found to significantly increase antibody responses for each WIV compared to WIV alone. Furthermore, we observed the presence of cell-mediated immune responses in chickens that received the BPL WIV combined with CpG ODN 2007. Based on these results, the BPL WIV + CpG ODN 2007 combination was the most effective vaccine at inducing adaptive immune responses against H9N2 AIV. Future studies should characterize mucosal adaptive immune responses to these vaccines.

Challenge for One Health: Co-Circulation of Zoonotic H5N1 and H9N2 Avian Influenza Viruses in Egypt

Highly pathogenic avian influenza (HPAI) H5N1 viruses are currently endemic in poultry in Egypt. Eradication of the viruses has been unsuccessful due to improper application of vaccine-based control strategies among other preventive measures. The viruses have evolved rapidly with increased bird-to-human transmission efficacy, thus affecting both animal and public health. Subsequent spread of potentially zoonotic low pathogenic avian influenza (LPAI) H9N2 in poultry has also hindered efficient control of avian influenza. The H5N1 viruses acquired enhanced bird-to-human transmissibility by (1) altering amino acids in hemagglutinin (HA) that enable binding affinity to human-type receptors, (2) loss of the glycosylation site and 130 loop in the HA protein and (3) mutation of E627K in the PB2 protein to enhance viral replication in mammalian hosts. The receptor binding site of HA of Egyptian H9N2 viruses has been shown to contain the Q234L substitution along with a H191 mutation, which can increase human-like receptor specificity. Therefore, co-circulation of H5N1 and H9N2 viruses in poultry farming and live bird markets has increased the risk of human exposure, resulting in complication of the epidemiological situation and raising a concern for potential emergence of a new influenza A virus pandemic. For efficient control of infection and transmission, the efficacy of vaccine and vaccination needs to be improved with a comprehensive control strategy, including enhanced biosecurity, education, surveillance, rapid diagnosis and culling of infected poultry.

Induction profiles of mRNA of toll like receptors and cytokines in chickens pre-exposed to low pathogenic avian influenza H9N2 virus followed by challenge with highly pathogenic avian influenza H5N1 virus

Herein, the induction of TLRs and cytokines in chickens pre-exposed to low pathogenic avian influenza H9N2 virus followed by challenge with highly pathogenic avian influenza (HPAI) H5N1 virus was studied. Four groups (1-4) of chickens inoculated with 10⁶ EID₅₀ of H9N2 virus were challenged with 10⁶ EID₅₀ of H5N1 virus on days 1, 3, 7 and 14 post H9N2 inoculation, respectively. In groups (1-4) TLRs and cytokines induction was studied in chicken PBMCs on day 3 post H5N1 challenge. In H5N1 control group TLRs (1, 2, 5 and 7) cytokines (IFNα, IFNβ, IFNγ, IL1β, IL2, IL4, IL8 and TGF β3) were down regulated. In group 1 down regulation of cytokines and TLRs was similar to H5N1 control birds. Down regulation of TLRs and cytokines in H5N1 control and group 1 resulted death of all the chickens. In group 2, up-regulation of TLRs (3, 7 and 15) and induction of TNFα, IFNα, IFNβ, IFNγ aided virus clearance leading to survival of all the chickens. In group 3 significant up-regulation of TLRs (3, 4 and 15) and significant induction of cytokines (IFNγ, TNFα, IL1β, IL4, IL6, IL8, IL10 and TGF β3) was detected. In group 4 significant up-regulation of TLRs (2, 3, 7 and 15) and significant induction of cytokines (IFNγ, TNFα, IL1β, IL2, IL6, IL8 and IL10) was detected. In groups 3 and 4 simultaneous and significant induction of pro-inflammatory, antiviral and anti-inflammatory cytokine resulted cytokine dysregulation leading to death of (2/6) and (3/6) chickens respectively. Hence, the study revealed TLRs and cytokines role in modulating the H5N1 infection outcome in chickens pre-exposed to H9N2 virus.

Avian Respiratory Coinfection and Impact on Avian Influenza Pathogenicity in Domestic Poultry: Field and Experimental Findings

The avian respiratory system hosts a wide range of commensal and potential pathogenic bacteria and/or viruses that interact with each other. Such interactions could be either synergistic or antagonistic, which subsequently determines the severity of the disease complex. The intensive rearing methods of poultry are responsible for the marked increase in avian respiratory diseases worldwide. The interaction between avian influenza with other pathogens can guarantee the continuous existence of other avian pathogens, which represents a global concern. A better understanding of the impact of the interaction between avian influenza virus and other avian respiratory pathogens provides a better insight into the respiratory disease complex in poultry and can lead to improved intervention strategies aimed at controlling virus spread.

Oral immunization with a novel attenuated Salmonella Typhimurium encoding influenza HA, M2e and NA antigens protects chickens against H7N9 infection

Attenuated Salmonella strains constitute a promising technology for the development of efficient protein-based influenza vaccines. H7N9, a low pathogenic avian influenza (LPAI) virus, is a major public health concern and currently there are no effective vaccines against this subtype. Herein, we constructed a novel attenuated Salmonella Typhimurium strain for the delivery and expression of H7N9 hemagglutinin (HA), neuraminidase (NA) or the conserved extracellular domain of the matrix protein 2 (M2e). We demonstrated that the constructed Salmonella strains exhibited efficient HA, NA and M2e expressions, respectively, and the constructs were safe and immunogenic in chickens. Our results showed that chickens immunized once orally with Salmonella (Sal) mutants encoding HA (Sal-HA), M2e (Sal-M2e) or NA (Sal-NA), administered either alone or in combination, induced both antigen-specific humoral and cell mediated immune (CMI) responses, and protected chickens against the lethal H7N9 challenge. However, chickens immunized with Sal-HA+Sal-M2e+Sal-NA vaccine constructs exhibited efficient mucosal and CMI responses compared to the chickens that received only Sal-HA, Sal-M2e or Sal-M2e+Sal-NA vaccine. Further, chickens immunized with Sal-HA+Sal-M2e+Sal-NA constructs cleared H7N9 infection at a faster rate compared to the chickens that were vaccinated with Sal-HA, Sal-M2e or Sal-M2e+Sal-NA, as indicated by the reduced viral shedding in cloacal swabs of the immunized chickens. We conclude that this vaccination strategy, based on HA, M2e and NA, stimulated efficient induction of immune protection against the lethal H7N9 LPAI virus and, therefore, further studies are warranted to develop this approach as a potential prophylaxis against LPAI viruses affecting poultry birds.

Antibody responses to avian influenza viruses in wild birds broaden with age

For viruses such as avian influenza, immunity within a host population can drive the emergence of new strains by selecting for viruses with novel antigens that avoid immune recognition. The accumulation of acquired immunity with age is hypothesized to affect how influenza viruses emerge and spread in species of different lifespans. Despite its importance for understanding the behaviour of avian influenza viruses, little is known about age-related accumulation of immunity in the virus's primary reservoir, wild birds. To address this, we studied the age structure of immune responses to avian influenza virus in a wild swan population (Cygnus olor), before and after the population experienced an outbreak of highly pathogenic H5N1 avian influenza in 2008. We performed haemagglutination inhibition assays on sampled sera for five avian influenza strains and show that breadth of response accumulates with age. The observed age-related distribution of antibody responses to avian influenza strains may explain the age-dependent mortality observed during the highly pathogenic H5N1 outbreak. Age structures and species lifespan are probably important determinants of viral epidemiology and virulence in birds.

Emerging Zoonotic Influenza A Virus Detection in Myanmar: Surveillance Practices and Findings

We describe 2-season, risk-based, virological surveillance for zoonotic avian influenza in Myanmar and report the first detection of influenza A subtypes H5N6 and H9N2 in Myanmar. The study focused mainly on the live bird markets in border townships, where illegal poultry importation from China usually takes place. The objective was to enhance early warning for low pathogenic avian influenza A(H7N9) incursion. The study followed the guidelines of the Food and Agriculture Organization (FAO) of the United Nations for influenza A(H7N9) surveillance in uninfected countries. The sampling strategy was risk-based at all sampling levels. Sample collection and laboratory analysis were carried out with the government of the Union of the Republic of Myanmar. Laboratory testing was according to a previously published FAO laboratory protocol and algorithm designed to detect a range of influenza A subtypes. Challenges to implementation are outlined. The study provided evidence that the H7N9 subtype had not entered Myanmar but detected other subtypes, including H5N6 and H9N2. Although there were logistical difficulties associated with nation-related issues, the results highlight the importance and feasibility of this risk-based active surveillance, which should be urgently established in other countries, especially those located at the east-southeast influenza epicenter.

Longitudinal Study of Avian Influenza and Newcastle Disease in Village Poultry, Mali, 2009-2011

Newcastle disease (ND) is endemic in West Africa, which has also experienced outbreaks of highly pathogenic avian influenza (AI) H5N1 since 2006. We aimed to estimate the prevalence and incidence of AI and ND in village poultry in Mali and to identify associated risk factors. A longitudinal serologic study was conducted between November 2009 and February 2011 using ELISA commercial kits to detect antibodies. Sera (5963) were collected from 4890 different poultry. AI was rare, with a seroprevalence of 2.9% (95% confidence interval [CI] 2.3-3.5) and a seroincidence rate of 0.7 birds per 100 bird-months at risk (95% CI 0.4-1.0). AI antibodies were short lived, with a seroreversion rate of 25.4 birds per 100 bird-months at risk (95% CI 19.0-31.7). Risk factors for AI were limited: temporal variation occurred, but proximity to a water body was a risk factor only when large populations of wild waterbirds were present. ND was very common, with seroprevalence of 68.9% (95% CI 61.9-76.0) and a seroincidence rate of 15.9 birds per 100 bird-months at risk (95% CI 11.9-19.8). ND seroreversion rate was 6.2 birds per 100 bird-months at risk (95% CI 3.6-8.9). Regarding risk factors for ND, temporal variations occurred, and ND was more likely to be present in the Sudanian agro-ecological zone than in the Sahelian zone, in chickens than in other species, in flocks with higher numbers of Guinea fowl, and in flocks that had access to a waterbody. Control efforts would benefit from further increasing the ND vaccination coverage of village poultry, although this was already quite high (54.9%) for an African country. Seroconversion seemed satisfactory in vaccinated poultry, since 90.0% (95% CI 87.6-92.4) of these had ND antibodies. Further research should investigate the apparent lack of an epidemiologic role of domestic ducks for AI in Mali (unlike in Southeast Asia) and the potential role of Guinea fowl as a reservoir for ND.

Protection Afforded by a Recombinant Turkey Herpesvirus-H5 Vaccine Against the 2014 European Highly Pathogenic H5N8 Avian Influenza Strain

A highly pathogenic avian influenza (HPAI) H5N8 (clade 2.3.4.4) virus, circulating in Asia (South Korea, Japan, and southern China) since the beginning of 2014, reached the European continent in November 2014. Germany, the Netherlands, the United Kingdom, Italy, and Hungary confirmed H5N8 infection of poultry farms of different species and of several wild bird species. Unlike the Asian highly pathogenic (HP) H5N1, this HP H5N8 also went transatlantic and reached the American West Coast by the end of 2014, affecting wild birds as well as backyard and commercial poultry. This strain induces high mortality and morbidity in Galliformes, whereas wild birds seem only moderately affected. A recombinant turkey herpesvirus (rHVT) vector vaccine expressing the H5 gene of a clade 2.2 H5N1 strain (rHVT-H5) previously demonstrated a highly efficient clinical protection and reduced viral excretion against challenge with Asian HP H5N1 strains of various clades (2.2, 2.2.1, 2.2.1.1, 2.1.3, 2.1.3.2, and 2.3.2.1) and was made commercially available in various countries where the disease is endemic. To evaluate the protective efficacy of the rHVT-H5 vaccine against the first German H5N8 turkey isolate (H5N8 GE), a challenge experiment was set up in specific-pathogen-free (SPF) chickens, and the clinical and excretional protection was evaluated. SPF chickens were vaccinated subcutaneously at 1 day old and challenged oculonasally at 4 wk of age with two viral dosages, 10(5) and 10(6) 50% egg infective doses. Morbidity and mortality were monitored daily in unvaccinated and vaccinated groups, whereas viral shedding by oropharyngeal and cloacal routes was evaluated at 2, 5, 9, and 14 days postinoculation (dpi). Serologic monitoring after vaccination and challenge was also carried out. Despite its high antigenic divergence of the challenge H5N8 strain, a single rHVT-H5 vaccine administration at 1 day old resulted in a full clinical protection against challenge and a significant reduction of viral shedding in the vaccinated birds.

Competition between influenza A virus subtypes through heterosubtypic immunity modulates re-infection and antibody dynamics in the mallard duck

Our overall hypothesis is that host population immunity directed at multiple antigens will influence the prevalence, diversity and evolution of influenza A virus (IAV) in avian populations where the vast subtype diversity is maintained. To investigate how initial infection influences the outcome of later infections with homologous or heterologous IAV subtypes and how viruses interact through host immune responses, we carried out experimental infections in mallard ducks (Anas platyrhynchos). Mallards were pre-challenged with an H3N8 low-pathogenic IAV and were divided into six groups. At five weeks post H3N8 inoculation, each group was challenged with a different IAV subtype (H4N5, H10N7, H6N2, H12N5) or the same H3N8. Two additional pre-challenged groups were inoculated with the homologous H3N8 virus at weeks 11 and 15 after pre-challenge to evaluate the duration of protection. The results showed that mallards were still resistant to re-infection after 15 weeks. There was a significant reduction in shedding for all pre-challenged groups compared to controls and the outcome of the heterologous challenges varied according to hemagglutinin (HA) phylogenetic relatedness between the viruses used. There was a boost in the H3 antibody titer after re-infection with H4N5, which is consistent with original antigenic sin or antigenic seniority and suggest a putative strategy of virus evasion. These results imply competition between related subtypes that could regulate IAV subtype population dynamics in nature. Collectively, we provide new insights into within-host IAV complex interactions as drivers of IAV antigenic diversity that could allow the circulation of multiple subtypes in wild ducks.

Adaptive Heterosubtypic Immunity to Low Pathogenic Avian Influenza Viruses in Experimentally Infected Mallards

Mallards are widely recognized as reservoirs for Influenza A viruses (IAV); however, host factors that might prompt seasonality and trends in subtype diversity of IAV such as adaptive heterosubtypic immunity (HSI) are not well understood. To investigate this, we inoculated mallards with a prevailing H3N8 low pathogenic avian influenza virus (LPAIV) subtype in waterfowl to determine if prior infection with this virus would be protective against heterosubtypic infections with the H4N6, H10N7 and H14N5 LPAIV subtypes after one, two and three months, respectively. Also, we investigated the effect of cumulative immunity after sequential inoculation of mallards with these viruses in one-month intervals. Humoral immunity was assessed by microneutralization assays using a subset of representative LPAIV subtypes as antigens. Our results indicate that prior inoculation with the H3N8 virus confers partial protective immunity against subsequent heterosubtypic infections with the robustness of HSI related to the phylogenetic similarity of the HA protein of the strains used. Furthermore, induced HSI was boosted and followed by repeated exposure to more than one LPAIV subtype. Our findings provide further information on the contributions of HSI and its role in the dynamics of IAV subtype diversity in mallards.

On the extinction probability in models of within-host infection: the role of latency and immunity

Not every exposure to virus establishes infection in the host; instead, the small amount of initial virus could become extinct due to stochastic events. Different diseases and routes of transmission have a different average number of exposures required to establish an infection. Furthermore, the host immune response and antiviral treatment affect not only the time course of the viral load provided infection occurs, but can prevent infection altogether by increasing the extinction probability. We show that the extinction probability when there is a time-dependent immune response depends on the chosen form of the model-specifically, on the presence or absence of a delay between infection of a cell and production of virus, and the distribution of latent and infectious periods of an infected cell. We hypothesise that experimentally measuring the extinction probability when the virus is introduced at different stages of the immune response, alongside the viral load which is usually measured, will improve parameter estimates and determine the most suitable mathematical form of the model.

Prevalence and diversity of H9N2 avian influenza in chickens of Northern Vietnam, 2014

Despite their classification as low pathogenicity avian influenza viruses (LPAIV), A/H9N2 viruses cause significant losses in poultry in many countries throughout Asia, the Middle East and North Africa. To date, poultry surveillance in Vietnam has focused on detection of influenza H5 viruses, and there is limited understanding of influenza H9 epidemiology and transmission dynamics. We determined prevalence and diversity of influenza A viruses in chickens from live bird markets (LBM) of 7 northern Vietnamese provinces, using pooled oropharyngeal swabs collected from October to December 2014. Screening by real time RT-PCR revealed 1207/4900 (24.6%) of pooled swabs to be influenza A virus positive; overall prevalence estimates after accounting for pooling (5 swabs/pools) were 5.8% (CI 5.4–6.0). Subtyping was performed on 468 pooled swabs with M gene Ct < 26. No influenza H7 was detected; 422 (90.1%) were H9 positive; and 22 (4.7%) were H5 positive. There was no evidence was of interaction between H9 and H5 virus detection rates. We sequenced 17 whole genomes of A/H9N2, 2 of A/H5N6, and 11 partial genomes. All H9N2 viruses had internal genes that clustered with genotype 57 and were closely related to Chinese human isolates of A/H7N9 and A/H10N8. Using a nucleotide divergence cutoff of 98%, we identified 9 distinct H9 genotypes. Phylogenetic analysis suggested multiple introductions of H9 viruses to northern Vietnam rather than in-situ transmission. Further investigations of H9 prevalence and diversity in other regions of Vietnam are warranted to assess H9 endemicity elsewhere in the country.

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We report detection of highly pathogenic avian influenza (HPAI) from healthy chickens in Live Bird Markets of Vietnam. Because all breeds of domestic chickens are extremely susceptible to HPAI, we speculate that HPAI detections from market chickens may reflect infections that occur after arrival in the market. Alternatively, shedding of HPAI from healthy birds may reflect vaccine-induced protective immunity that mitigates disease but does not block viral infection.

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As many as 49% of all pooled surveillance swabs were positive for influenza A virus, corresponding to an overall Influenza A prevalence of 5.45% (95% Confidence Interval 5.4-6.0%).

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Low pathogenicity avian influenza (LPAI) H9N2 accounted for the vast majority of all influenza A detections in market chickens sampled from 9 northern provinces.

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To date there is no evidence to suggest an interaction effect between circulation of H5 and H9 viruses; however sampling strategies that involve pooling of surveillance swabs from multiple birds greatly complicates the assessment of co-infection rates or evaluation of epidemiological associations.