Effectiveness of different avian influenza (H5) vaccination regimens in layer chickens on the humoral immune response and interferon-alpha signalling immune marker

Highly pathogenic avian influenza H5N8 and H5N1 outbreaks in Algerian avian livestock production

Avian Alpha-influenza-virus (AIV) massively affects poultry, targeting mainly the respiratory tract for virus replication. Recently, two major H5N8 and H5N1 outbreaks caused tremendous losses in Algerian poultry. The clinical symptoms that had not been seen in the past didn't prompt a rapid reaction to control the epidemics. We report here the characteristics of these outbreaks and the epidemiological status of AIV in Algeria. Following autopsy observation samples from target organs were taken and analyzed by the classical real-time reverse transcription polymerase chain reaction (RRT-PCR). Specific PCR HA and NA identification was used for subtyping H5 and N1/N8 genes. Systemic damage was observed in the upper-respiratory tracts with hemorrhagic and congestive tracheas, lungs, proventriculus, gut, and cecal tonsils were bloody. Out of 77 positive cases 13 were H5N8, 8 H5N1, and 10 H5Nx strains. These findings raise questions about the strain's pathotype considering severe organ damage and high mortality.

HVT-vectored H7 vaccine protects chickens from lethal infection with the highly pathogenic H7N9 Avian influenza virus

Since mid-2016, the highly pathogenic H7N9 subtype avian influenza virus (AIV) has threatened both public health and the poultry industry. Although a vaccination strategy has been deemed imperative to manage the virus, the most commonly used inactivated vaccines today are susceptible to interference from maternal antibodies and associated with an over-reliance on humoral immunity. In response, we developed a recombination vaccine with the herpesvirus of turkeys (HVT) as the vector to squeeze HPAI H7N9 and assessed its protective efficiency in immunized chickens. By inserting an enhanced green fluorescent protein (EGFP) expression cassette (i.e., MCMV+EGFP+SV40 polyA) into the HVT065 and HVT066 positions, we obtained the recombinant HVT expressing EGFP (i.e., rHVT-EGFP). Electroporation and EGFP tags improved the efficiency of transfection compared with transfection using expression plasmids without any fluorescent labeling and traditional liposomes. Using limiting dilution analysis and ultrasonic cell disruption techniques, we screened and purified a cell-bound herpes virus based on rHVT-EGFP and consequently constructed a recombinant HVT expressing the hemagglutinin (HA) of H7N9 (i.e., rHVT-H7HA), which was able to proliferate similarly to the parental strain, stably pass for at least 15 generations in vitro, and replicate stably in multiple organs in vivo. After chickens were immunized with rHVT-H7HA, the average antibody titers reached up to 3 log2 at 35 d post-vaccination and remained stable. Those results suggest that rHVT-H7HA can protect chickens against H7N9 with a dose-independent immune protection rate of 90% and significantly reduce the lung virus titer 4 d post-challenge.

Identification of a Novel Insertion Site HVT-005/006 for the Generation of Recombinant Turkey Herpesvirus Vector

Turkey herpesvirus (HVT) has been widely used as a successful live virus vaccine against Marek's disease (MD) in chickens for more than five decades. Increasingly, HVT is also used as a highly effective recombinant vaccine vector against multiple avian pathogens. Conventional recombination, or recombineering, techniques that involve the cloning of viral genomes and, more recently, gene editing methods have been used for the generation of recombinant HVT-based vaccines. In this study, we used NHEJ-dependent CRISPR/Cas9-based approaches to insert the mCherry cassette for the screening of the HVT genome and identifying new potential sites for the insertion of foreign genes. A novel intergenic site HVT-005/006 in the unique long (UL) region of the HVT genome was identified, and mCherry was found to be stably expressed when inserted at this site. To confirm whether this site was suitable for the insertion of other exogenous genes, haemagglutinin (HA) of the H9N2 virus was inserted into this site, and a recombinant HVT-005/006-HA was rescued. The recombinant HVT-HA can grow well and express HA protein stably, which demonstrated that HVT-005/006 is a promising site for the insertion of foreign genes.

A novel epitope-blocking ELISA for specific and sensitive detection of antibodies against H5-subtype influenza virus hemagglutinin

Background

H5-subtype highly pathogenic (HP) avian influenza viruses (AIVs) cause high mortality in domestic birds and sporadic infections in humans with a frequently fatal outcome, while H5N1 viruses have pandemic potential. Due to veterinary and public health significance, these HPAIVs, as well as low pathogenicity (LP) H5-subtype AIVs having a propensity to mutate into HP viruses, are under epidemiologic surveillance and must be reported to the World Organization for Animal Health (OIE). Our previous work provided a unique panel of 6 different monoclonal antibodies (mAbs) against H5 hemagglutinin (HA), which meets the demand for high-specificity tools for monitoring AIV infection and vaccination in poultry. In this study, we selected one of these mAbs to develop an epitope-blocking (EB) ELISA for detecting H5 subtype-specific antibodies in chicken sera (H5 EB-ELISA).

Methods

In the H5 EB-ELISA, H5 HA protein produced in a baculovirus-expression vector system was employed as a coating antigen, and the G-7-27-18 mAb was employed as a blocking antibody. The performance characteristics of the assay were evaluated by testing 358 sera from nonimmunized chickens and chickens immunized with AIVs of the H1–H16 subtypes or recombinant H5 HA antigen to obtain the reference and experimental antisera, respectively. The samples were classified as anti-H5 HA positive or negative based on the results of the hemagglutination inhibition (HI) assay, the gold standard in subtype-specific serodiagnosis.

Results

The H5 EB-ELISA correctly discriminated between the anti-H5 HA negative sera, including those against the non-H5 subtype AIVs, and sera positive for antibodies against the various-origin H5 HAs. Preliminary validation showed 100% analytical and 97.6% diagnostic specificities of the assay and 98.0% and 99.1% diagnostic sensitivities when applied to detect the anti-H5 HA antibodies in the reference and experimental antisera, respectively.

Conclusions

The H5 EB-ELISA performed well in terms of diagnostic estimates. Thus, further optimization and validation work using a larger set of chicken sera and receiver operating characteristic (ROC) analysis are warranted. Moreover, the present assay provides a valuable basis for developing multispecies screening tests for birds or diagnostic tests for humans.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12985-021-01564-6.

Different kinetics of chicken interferon-alpha signalling transduction responses following immunization of broiler chickens with different Newcastle disease virus vaccines and infection with virulent genotype VIId strain

Newcastle disease virus (NDV) is a highly contagious and notifiable avian disease leading to grave economic losses in the poultry industry. Although the immune responses against NDV have been widely investigated, little is known regarding the virus interaction with the host innate immune responses. In this study, we tested the effect of different commercially applied Newcastle disease vaccines as well as virulent NDV genotype VIId on the expression pattern of the upstream regulator and downstream effector genes related to chicken interferon-alpha (chIFNα) signalling transduction pathway. Using quantitative real-time PCR analysis, mild transient induction of chIFNα-inducible genes was detected in bird spleen 72 h post-vaccination (hpv) with either live LaSota (respiratory) or VG/GA (enteric) strains. Vaccination with the enteric VG/GA strain led to stimulation of the investigated pathway as early as 24 hpv which continued up to 7 days in bird caecal tonsils. Subcutaneous injection with inactivated LaSota oil adjuvant-based vaccine led to continual stimulation of the investigated pathway up to 7 days post-vaccination (dpv). The recombinant herpesvirus of turkey (rHVT) - NDV vaccine led to remarkable stimulation of all the tested cytokines up to 17 dpv in comparison with LaSota and VG/GA NDV vaccines. Stronger but transient activation of all the tested cytokines was detected in spleens during the first 24 h post-challenge with virulent NDV (vNDV) which reduced gradually and diminished later due to the virus-induced lymphocytic depletion. This study will aid in the discovery of new approaches to control NDV.

Evaluation in broilers of aerosolized nanoparticles vaccine encapsulating imuno-stimulant and antigens of avian influenza virus/Mycoplasma gallisepticum

Background

The global prevalence of economic primary infection of poultry by H9N2 virus, including the Lineage A, panzootic group ME1, and associated with secondary infection by Mycoplasma gallisepticum (MG), is alarming to the sustainability of the poultry sector. This research evaluated in broilers the immunity and protection induced by aerosolization of liposomal nanoparticles vaccine, encapsulating antigens of H9N2 virus and MG, with or without the incorporation of Echinacea extract (EE) immuno-stimulant. Six different treatments (TRTs) of broilers were included in the experimental design, with three replicate pens/TRT and stocking of 20 day-old birds/replicate.

Results

The tracheobronchial washings of birds subjected to aerosolization of liposomal nanoparticles, encapsulating antigens of H9N2 and MG and EE had the highest significant mean levels of each of IgA and IgG specific to H9N2 and MG, associated with lowest tracheal MG colonization, tracheal H9N2 recovery, tracheal histopathologic lesions, mortality, and best performance in body weight and feed conversion compared to all other challenged birds allocated to different treatments (P < 0.05). However, the control broilers, free from challenge with MG and H9N2, had the lowest mortality and tracheal lesions, and the highest production performance.

Conclusion

The aerosolization of liposomal nanoparticles, encapsulating antigens of H9N2 and MG and EE resulted in enough local immunity for protection of broilers against infection, and in attaining the highest production performance in challenged birds. The potential implication of vaccinating with safe killed nanoparticle vaccines is of utmost importance to the global poultry sector.

Prime-Boost Vaccination With a Novel Hemagglutinin Protein Produced in Bacteria Induces Neutralizing Antibody Responses Against H5-Subtype Influenza Viruses in Commercial Chickens

The highly pathogenic (HP) avian influenza virus (AIV), H5N1 and reassortant H5-subtype HPAIVs, H5N2, H5N6, and H5N8, cause high mortality in domestic birds, resulting in economic losses in the poultry industry. H5N1 and H5N6 also pose significant public health risks and H5N1 viruses are a permanent pandemic threat. To control HPAIVs, eukaryotic expression systems have traditionally been exploited to produce vaccines based on hemagglutinin (HA), a protective viral antigen. In contrast, we used a bacterial expression system to produce vaccine targeting the HA protein. A fragment of the HA ectodomain from H5N1, with a multibasic cleavage site deletion, was expressed in Escherichia coli, refolded, and chromatographically purified from inclusion bodies. The resulting antigen, rH5-E. coli, was validated in terms of conformational integrity and oligomerization status. Previously, the protective efficacy of rH5-E. coli adjuvanted with aluminum hydroxide, has been positively verified by challenging the specific pathogen-free layer chickens with homologous and heterologous H5N1 HPAIVs. Protection was provided primarily by the H5 subtype-specific antibodies, as detected in the FluAC H5 test. The present studies were conducted to assess the performance of alum-adjuvanted rH5-E. coli in commercial birds. Broiler chickens were vaccinated twice with 25 μg of rH5-E. coli at 2- and 4-week intervals, while the layer chickens were vaccinated with 5- to 25-μg antigen doses at 4- and 6-week intervals. Post-vaccination sera were analyzed for anti-H5 HA antibodies, using homologous ELISA and heterologous FluAC H5 and hemagglutination inhibition (HI) tests. Prime-boost immunizations with rH5-E. coli elicited H5 HA-specific antibodies in all the chickens tested. Two antigen doses administered at 4- or 6-week intervals were sufficient to induce neutralizing antibodies against H5-subtype HAs; however, they were ineffective when applied with a 2-week delay. In the layers, 80% to 100% of individuals developed antibodies that were active in the FluAC H5 and/or HI tests. A dose-sparing effect was seen when using the longer prime-boost interval. In the broiler chickens, 62.5% positivity was achieved in the FluAC H5 and/or HI tests. The trials confirmed the vaccine potential of rH5-E. coli and provided indications for anti-influenza vaccination with respect to the chicken type and immunization scheme.

Influence of Marek's disease virus vaccines on chicken melanoma differentiation-associated gene 5-dependent-type I interferon signal transduction pathway with a highlight on their secondary impact on the immune responses post Newcastle disease virus vaccination

Marek's disease virus (MDV) leads to a lytic infection of B-lymphocytes in chickens, and also latently infects T-lymphocytes. Although Marek's disease vaccines have been widely in use, little is known about the innate immune response of this important livestock vaccine. In this study, we tested the effect of different commercially applied Marek's disease vaccines on the expression pattern of selected genes related to chicken interferon-alpha (chIFN-α) (melanoma differentiation associated gene 5 "MDA5″ dependent) signal transduction pathway. Both MDV serotype I (Rispens) and serotype III (Herpesvirus of turkey "HVT") vaccines could stimulate MDA5 dependent-type I interferon response as early as three days post vaccination in a dose-dependent manner. The stimulation continued up to 10 days in the instance of HVT vaccine and declined in the case of Rispens. Surprisingly, increasing the doses of the two vaccines led to dose-dependent down-regulation in the expression pattern of the investigated pathway, five and ten days post vaccination. Additionally, to shed the light on the consequent effect on the immune responses of the other viral vaccine, another experimental model based on Newcastle disease virus (NDV) vaccines was designed using HVT, HVT-VP2 and Rispens MDV vaccines. The three MDV vaccines were found to reduce chicken humoral immune response post NDV vaccination. However, only Rispens and HVT-VP2 had suppressive effects on the expression of MDA5-dependent-chIFN-α related cytokines. Consistent with this finding, the protection rate and NDV- humoral immune response post challenge with virulent NDV strain was lower in case of Rispens and HVT-VP2 vaccines.