Passive antibody transfer in chickens to model maternal antibody after avian influenza vaccination

Immunoadjuvant efficacy of CpG plasmids for H9N2 avian influenza inactivated vaccine in chickens with maternal antibodies

Maternal-derived antibodies (MDAs) are one of reasons why vaccination with the H9N2 inactivated whole virus (IWV) vaccine failed in poultry. Unmethylated CpG motif-containing oligodeoxynucleotides (CpG ODN) shows great potential to overcome MDAs interference in mammals, but whether it has similar characteristics in poultry is still unknown. In the present study, different classes and various copies of CpG ODN motifs were cloned into two different plasmids (pCDNA3.1 or T vector). Immunomodulatory activities and immunoadjuvant efficacy of these CpG ODN plasmids were tested in vitro and in vivo in the presence of passively transferred antibodies (PTAs) that were used to mimic MDAs. Results showed that the T vector enriched with 30 copies of CpG-A ODN and 20 copies of CpG-B ODN (T-CpG-AB) significantly up-regulated mRNA expression of chicken-interferon-α (ch-IFN-α), chicken-interferon-β (ch-IFN-β) and chicken-interleukin-12 protein 40 (ch-IL-12p40). When administered as adjuvant of the H9N2 IWV vaccine, the minimal dose of T-CpG-AB plasmid was 30 µg per one-day-old chicken, which could induce strong humoral immune responses in the presence of PTAs. Furthermore, T-CpG-AB plasmid-based vaccine triggered both strong humoral immune responses and cytokines expression in the presence of PTAs in chickens. Overall, our findings suggest that T-CpG-AB plasmid can be an excellent adjuvant candidate for the H9N2 IWV vaccine to overcome MDAs interference in chickens.

Development of an Inactivated Avian Influenza Virus Vaccine against Circulating H9N2 in Chickens and Ducks

Avian influenza virus (AIV) subtype H9N2 is the most widespread AIV in poultry worldwide, causing great economic losses in the global poultry industry. Chickens and ducks are the major hosts and play essential roles in the transmission and evolution of H9N2 AIV. Vaccines are considered an effective strategy for fighting H9N2 infection. However, due to the differences in immune responses to infection, vaccines against H9N2 AIV suitable for use in both chickens and ducks have not been well studied. This study developed an inactivated H9N2 vaccine based on a duck-origin H9N2 AIV and assessed its effectiveness in the laboratory. The results showed that the inactivated H9N2 vaccine elicited significant haemagglutination inhibition (HI) antibodies in both chickens and ducks. Virus challenge experiments revealed that immunization with this vaccine significantly blocked virus shedding after infection by both homogenous and heterologous H9N2 viruses. The vaccine was efficacious in chicken and duck flocks under normal field conditions. We also found that egg-yolk antibodies were produced by laying birds immunized with the inactivated vaccine, and high levels of maternal antibodies were detected in the serum of the offspring. Taken together, our study showed that this inactivated H9N2 vaccine could be extremely favourable for the prevention of H9N2 in both chickens and ducks.

Whole-genome characterization of avian picornaviruses from diarrheic broiler chickens co-infected with multiple picornaviruses in Iran

Gastrointestinal symptoms in poultry are caused by several factors, such as infecting viruses. Several avian picornaviruses can cause diarrhea in these valuable animals. Poultry flocks in Iran suffer from gastrointestinal diseases, and information on picornaviruses is limited. In this study, two genera of avian picornaviruses were isolated from poultry and identified by the viral metagenomics. Fecal samples were collected from broiler chicken flocks affected with diarrhea from Gilan province Iran. The results showed that Eastern chicken flocks carried two genera of picornaviridae belonging to Sicinivirus A (SiV A) and Megrivirus C (MeV C). The Western chicken flocks carried SiV A based on whole-genome sequencing data. SiV A had type II ^IRES and MeV C contained a type IVB ^IRES 5'UTR. Phylogenetic results showed that all these three picornaviruses were similar to the Hungarian isolates. Interestingly, two different picornavirus genera were simultaneously co-infected with Eastern flocks. This phenomenon could increase and facilitate the recombination and evolution rate of picornaviruses and consequently cause this diversity of gastrointestinal diseases in poultry. This is the first report and complete genome sequencing of Sicinivirus and Megrivirus in Iran. Further studies are needed to evaluate the pathogenic potential of these picornaviruses.

Efficacy of a recombinant turkey herpesvirus (H9) vaccine against H9N2 avian influenza virus in chickens with maternal-derived antibodies

Although vaccines have been widely used for many years, they have failed to control H9N2 avian influenza virus (AIV) in the field in China. The high level of maternal-derived antibodies (MDAs) against H9N2 virus contributes to the H9N2 influenza vaccine failure in poultry. The study aimed to generate a new vaccine to overcome MDAs interference in H9N2 vaccination in chickens. We used turkey herpesvirus (HVT) as a vaccine vector to express H9 hemagglutinin (HA) proteins. The recombinant HVT expressing H9 HA proteins (rHVT-H9) was successfully generated and characterized in primary chicken embryonic fibroblasts (CEFs). Western blot and indirect immunofluorescence assay (IFA) showed that the rHVT-H9 consistently expressed HA proteins. In addition, the rHVT-H9 had similar growth kinetics to the parent HVT. Preliminary animal experiments showed that compared to the conventional inactivated whole virus (IWV) vaccine, the rHVT-H9 stimulated robust humoral immunity in chickens with passively transferred antibodies (PTAs) that were used to mimic MDAs. Transmission experiments showed that the rHVT-H9 induced both humoral and cellular immunity in chickens with PTAs. Furthermore, we used mathematical models to quantify the vaccine's efficacy in preventing the transmission of H9N2 AIV. The results showed that the rHVT-H9 reduced the virus shedding period and decreased the reproduction ratio (R) value in chickens with PTAs after homologous challenge. However, the vaccination in this trial did not yet bring R < 1. In summary, we generated a new rHVT-H9 vaccine, which stimulated strong humoral and cellular immunity, reducing virus shedding and transmission of H9N2 AIV even in the presence of PTAs in chickens.

Maternal-derived antibodies hinder the antibody response to H9N2 AIV inactivated vaccine in the field

The H9N2 subtype avian influenza virus (AIV) inactivated vaccine has been used extensively in poultry farms, but it often fails to stimulate a sufficiently high immune response in poultry in the field, although it works well in laboratory experiments; hence, the virus still causes economic damage every year and poses a potential threat to public health. Based on surveillance data collected in the field, we found that broilers with high levels of maternal-derived antibodies (MDAs) against H9N2 virus did not produce high levels of antibodies after vaccination with a commercial H9N2 inactivated vaccine. In contrast, specific pathogen-free (SPF) chickens without MDAs responded efficiently to that vaccination. When MDAs were mimicked by administering passively transferred antibodies (PTAs) into SPF chickens in the laboratory, similar results were observed: H9N2-specific PTAs inhibited humoral immunity against the H9N2 inactivated vaccine, suggesting that H9N2-specific MDAs might hinder the generation of antibodies when H9N2 inactivated vaccine was used. After challenge with homologous H9N2 virus, the virus was detected in oropharyngeal swabs of the vaccinated and unvaccinated chickens with PTAs but not in the vaccinated chickens without PTAs, indicating that H9N2-specific MDAs were indeed one of the reasons for H9N2 inactivated vaccine failure in the field. When different titers of PTAs were used to mimic MDAs in SPF chickens, high (HI = 12 log2) and medium (HI = log 9 log2) titers of PTAs reduced the generation of H9N2-specific antibodies after the first vaccination, but a booster dose would induce a high and faster humoral immune response even of PTA interference. This study strongly suggested that high or medium titers of MDAs might explain H9N2 inactivated vaccine failure in the field.

Immunomodulatory and antioxidant effects of hydroxytyrosol in cyclophosphamide-induced immunosuppressed broilers

As an important olive component, hydroxytyrosol (HT) has good medicinal and health effects. However, its importance in alleviating immune suppression in broilers has not been established. Therefore, we aimed at evaluating the immunomodulatory and antioxidant effects of HT in immune suppressed broilers. Immune suppressed broiler models were established via intraperitoneal injection of 80 mg/kg cyclophosphamide (Cy). Thirty two Cobb 500 male broilers were randomly allocated into 4 groups of 8 each. Broilers in the model (Cy) and HT treatment (Cy+HT) groups were intraperitoneally administered with Cy (80 mg/kg BW) once a day for 3 d. From the 4th d, broilers in the Cy+HT and HT groups were treated with 0.5 mL of 200 mg/L HT solution, once a day, for 7 d. The Cy and Con groups were orally administered with normal saline. On the 14th and 28th d, serum and duodenal samples were obtained for testing. It was found that HT increased villi height (VH)/crypt depth (CD) ratio in the duodenum and suppressed serum tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) levels. Moreover, it elevated the expressions of CD4+ and CD8+ T lymphocytes. HT upregulated the mRNA expression levels of interleukin-2 (IL-2), interleukin-4 (IL-4), and interleukin-10 (IL-10), enhanced the activity of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and downregulated malondialdehyde (MDA) levels in Cy-induced immune-suppressed broilers. In conclusion, HT can alleviate immune-suppression as well as enhance immunity and antioxidant activities in the local mucosa of small intestines in broilers. Therefore, it can be used as an immune stimulant. More studies should be performed to confirm our findings and to elucidate on the mechanisms of HT.

Infectious Bronchitis Virus (Gammacoronavirus) in Poultry Farming: Vaccination, Immune Response and Measures for Mitigation

Infectious bronchitis virus (IBV) poses significant financial and biosecurity challenges to the commercial poultry farming industry. IBV is the causative agent of multi-systemic infection in the respiratory, reproductive and renal systems, which is similar to the symptoms of various viral and bacterial diseases reported in chickens. The avian immune system manifests the ability to respond to subsequent exposure with an antigen by stimulating mucosal, humoral and cell-mediated immunity. However, the immune response against IBV presents a dilemma due to the similarities between the different serotypes that infect poultry. Currently, the live attenuated and killed vaccines are applied for the control of IBV infection; however, the continual emergence of IB variants with rapidly evolving genetic variants increases the risk of outbreaks in intensive poultry farms. This review aims to focus on IBV challenge-infection, route and delivery of vaccines and vaccine-induced immune responses to IBV. Various commercial vaccines currently have been developed against IBV protection for accurate evaluation depending on the local situation. This review also highlights and updates the limitations in controlling IBV infection in poultry with issues pertaining to antiviral therapy and good biosecurity practices, which may aid in establishing good biorisk management protocols for its control and which will, in turn, result in a reduction in economic losses attributed to IBV infection.

Novel Recombinant Newcastle Disease Virus-Based In Ovo Vaccines Bypass Maternal Immunity to Provide Full Protection from Early Virulent Challenge

Newcastle disease (ND) is one of the most economically important poultry diseases. Despite intensive efforts with current vaccination programs, this disease still occurs worldwide, causing significant mortality even in vaccinated flocks. This has been partially attributed to a gap in immunity during the post-hatch period due to the presence of maternal antibodies that negatively impact the replication of the commonly used live vaccines. In ovo vaccines have multiple advantages and present an opportunity to address this problem. Currently employed in ovo ND vaccines are recombinant herpesvirus of turkeys (HVT)-vectored vaccines expressing Newcastle disease virus (NDV) antigens. Although proven efficient, these vaccines have some limitations, such as delayed immunogenicity and the inability to administer a second HVT vaccine post-hatch. The use of live ND vaccines for in ovo vaccination is currently not applicable, as these are associated with high embryo mortality. In this study, recombinant NDV-vectored experimental vaccines containing an antisense sequence of avian interleukin 4 (IL4R) and their backbones were administered in ovo at different doses in 18-day-old commercial eggs possessing high maternal antibodies titers. The hatched birds were challenged with virulent NDV at 2 weeks-of-age. Post-hatch vaccine shedding, post-challenge survival, challenge virus shedding, and humoral immune responses were evaluated at multiple timepoints. Recombinant NDV (rNDV) vaccinated birds had significantly reduced post-hatch mortality compared with the wild-type LaSota vaccine. All rNDV vaccines were able to penetrate maternal immunity and induce a strong early humoral immune response. Further, the rNDV vaccines provided protection from clinical disease and significantly decreased virus shedding after early virulent NDV challenge at two weeks post-hatch. The post-challenge hemagglutination-inhibition antibody titers in the vaccinated groups remained comparable with the pre-challenge titers, suggesting the capacity of the studied vaccines to prevent efficient replication of the challenge virus. Post-hatch survival after vaccination with the rNDV-IL4R vaccines was dose-dependent, with an increase in survival as the dose decreased. This improved survival and the dose-dependency data suggest that novel attenuated in ovo rNDV-based vaccines that are able to penetrate maternal immunity to elicit a strong immune response as early as 14 days post-hatch, resulting in high or full protection from virulent challenge, show promise as a contributor to the control of Newcastle disease.

Newcastle disease virus transmission dynamics in wild peridomestic birds in the United Arab Emirates

To understand the dynamics of a pathogen in an animal population, one must assess how the infection status of individuals changes over time. With wild animals, this can be very challenging because individuals can be difficult to trap and sample, even more so since they are tested with imperfect diagnostic techniques. Multi-event capture-recapture models allow analysing longitudinal capture data of individuals whose infection status is assessed using imperfect tests. In this study, we used a two-year dataset from a longitudinal field study of peridomestic wild bird populations in the United Arab Emirates during which thousands of birds from various species were captured, sampled and tested for Newcastle disease virus exposure using a serological test. We developed a multi-event capture-recapture model to estimate important demographic and epidemiological parameters of the disease. The modelling outputs provided important insights into the understanding of Newcastle disease dynamics in peridomestics birds, which varies according to ecological and epidemiological parameters, and useful information in terms of surveillance strategies. To our knowledge, this study is the first attempt to model the dynamics of Newcastle disease in wild bird populations by combining longitudinal capture data and serological test results. Overall, it showcased that multi-event capture-recapture models represent a suitable method to analyse imperfect capture data and make reliable inferences on infectious disease dynamics in wild populations.

Protection of Chickens with Maternal Immunity Against Avian Influenza Virus (AIV) by Vaccination with a Novel Recombinant Newcastle Disease Virus Vector

Newcastle disease virus (NDV) vectors expressing avian influenza virus (AIV) hemagglutinin of subtype H5 protect specific pathogen-free chickens from Newcastle disease and avian influenza. However, maternal AIV antibodies (AIV-MDA+) are known to interfere with active immunization by influencing vaccine virus replication and gene expression, resulting in inefficient protection. To overcome this disadvantage, we inserted a transgene encoding a truncated soluble hemagglutinin (HA) in addition to the gene encoding membrane-bound HA from highly pathogenic avian influenza virus (HPAIV) H5N1 into lentogenic NDV Clone 30 genome (rNDVsolH5_H5) to overexpress H5 antigen. Vaccination of 3-wk-old AIV-MDA+ chickens with rNDVsolH5_H5 and subsequent challenge infection with HPAIV H5N1 3 wk later resulted in 100% protection. Vaccination of younger chickens with higher AIV-MDA levels 1 and 2 wk after hatch resulted in protection rates of 40% and 85%, respectively. However, all vaccinated chickens showed strongly reduced shedding of challenge virus compared with age-matched, nonvaccinated control chickens. All control chickens succumbed to the HPAIV infection with a grading in disease progression between the three groups, indicating the influence of AIV-MDAs even at a low level. Furthermore, the shedding and serologic data gathered after immunization indicate sufficient replication of the vaccine virus, which leads to the assumption that lower protection rates in younger AIV-MDA+ chickens are caused by an H5 antigen-specific block and not by the interference of the AIV-MDA and the vaccine virus itself. In summary, solid protective efficacy and reduced virus transmission were achieved in 3-wk-old AIV-MDA+ chickens, which is relevant especially in regions endemically infected with HPAIV H5N1.

Surveillance of multiple subtype specific antibodies against avian influenza viruses among egg yolk in wild ducks from northeast China, 2017-2019

Over the past decade, various avian influenza viruses have been isolated from wild ducks found in the northeast of China. To monitor the prevalence of multiple subtype specific AIVs antibodies, 1705 wild ducks' eggs from six wetlands of northeast China were analyzed for surveillance of H1, H3, H5, and H7 AIVs antibodies by c-ELISA and HI test from Jan 2017 to Dec 2019. The results show that the combined frequency of multiple subtype specific AIVs antibodies were H1 (12.32%), H3 (8.15%), H5 (2.05%), and H7 (3.46%) respectively. Therefore, a detailed analysis of the geographical distribution of AIVs in China, and the risk factors for human infection is of vital importance. This study provides basic data for other researchers to deeply study AIVs distribution characteristics, and for governments to develop detailed measures to control the spread of AIVs.

IFNγ Production Profile in Turkeys of Different Immunological Status after TRT Vaccination

Introduction

Despite vaccination against avian metapneumoviruses (aMPV), cases of turkey rhinotracheitis (TRT) caused by aMPV field strains are frequently reported. Differences have been shown in the level of immune system stimulation after aMPV vaccination between turkeys that do and do not possess specific anti-aMPV maternally derived antibodies (MDA). The article describes the influence of MDA on the production of IFNγ in the spleen of aMPV-vaccinated turkeys.

Material and Methods

MDA+ or MDA- turkeys were vaccinated against TRT after hatching or on the 14^th day of life. Spleen samples were collected 3, 7, and 14 days post vaccination for mononuclear cell isolation. Real-time PCR, flow cytometry, and the enzyme-linked immunospot assay were used to evaluate the levels of IFNγ gene expression, production, and secretion by cells within the spleen samples.

Results

Increased IFNγ gene expression was noticed after vaccination only in birds that did not possess MDA or possessed MDA at relatively low level (MDA+ birds vaccinated at 14 DOL). In all birds, an increased percentage of T lymphocytes producing IFNγ was recorded. The proportion of anti-aMPV IFNγ-secreting cells was increased only in MDA- birds.

Conclusion

Besides having a protective role, MDA are known to interfere with vaccination efficacy. The analysis of our results confirms that MDA can decrease the level of immune system stimulation after aMPV vaccination of turkeys.

Newcastle Disease Virus as a Vaccine Vector for 20 Years: A Focus on Maternally Derived Antibody Interference

It has been 20 years since Newcastle disease virus (NDV) was first used as a vector. The past two decades have witnessed remarkable progress in vaccine generation based on the NDV vector and optimization of the vector. Protective antigens of a variety of pathogens have been expressed in the NDV vector to generate novel vaccines for animals and humans, highlighting a great potential of NDV as a vaccine vector. More importantly, the research work also unveils a major problem restraining the NDV vector vaccines in poultry, i.e., the interference from maternally derived antibody (MDA). Although many efforts have been taken to overcome MDA interference, a lack of understanding of the mechanism of vaccination inhibition by MDA in poultry still hinders vaccine improvement. In this review, we outline the history of NDV as a vaccine vector by highlighting some milestones. The recent advances in the development of NDV-vectored vaccines or therapeutics for animals and humans are discussed. Particularly, we focus on the mechanisms and hypotheses of vaccination inhibition by MDA and the efforts to circumvent MDA interference with the NDV vector vaccines. Perspectives to fill the gap of understanding concerning the mechanism of MDA interference in poultry and to improve the NDV vector vaccines are also proposed.

Coexpression of soluble and membrane-bound avian influenza virus H5 by recombinant Newcastle disease virus leads to an increase in antigen levels

Newcastle disease virus (NDV) vectors expressing avian influenza virus (AIV) haemagglutinin (HA) of subtype H5 simultaneously protect chickens from Newcastle disease (ND) as well as avian influenza (AI). The expressed, membrane-bound surface protein HA is incorporated into virions while soluble HA has been described as a potent antigen. We tested whether co-expression of both HA variants from the same NDV vector increased the overall level of HA, which could be important for optimal immunogenicity. Recombinant NDVsolH5_H5 co-expressed membrane-bound H5 of highly pathogenic (HP) AIV H5N1, detectable in infected cells, and soluble H5, which was secreted into the supernatant. This virus was compared to recombinant NDV that express either membrane-bound (rNDVH5) or soluble H5 (rNDVsolH5). Replication in embryonated chicken eggs (ECEs) and in cell culture, as well as pathogenicity in ECEs, was not influenced by the second heterologous transcriptional unit. However, the co-expression of soluble H5 with membrane-bound H5 increased total protein level about 5.25-fold as detected by MS quantification. Hence, this virus is very interesting as a vaccine virus in chickens against HPAIV infections in situations in which previous H5-expressing NDVs have reached their limit, such as in the face of pre-existing AIV maternal immunity.

Hydrostatic Filtration Enables Large-Scale Production of Outer Membrane Vesicles That Effectively Protect Chickens against Gallibacterium anatis

Gallibacterium anatis is a Gram-negative opportunistic avian pathogen representing an emerging threat to poultry meat and egg production worldwide. To date, no vaccine able to effectively prevent the morbidity associated with G. anatis infections has been developed yet. Our group previously reported that inoculation of different combinations of G. anatis outer membrane vesicles (OMVs), FlfA and GtxA-N proteins is effective in preventing lesions caused by G. anatis infections in layer chickens. Here we report the testing of the efficacy as vaccine prototypes of G. anatis OMVs isolated by hydrostatic filtration, a simple technique that allows the cost-effective isolation of high yields of OMVs. Layer chickens were immunized with OMVs alone or in combination with FlfA and/or GtxA-N proteins. Subsequent challenge with a heterologous G. anatis strain showed that immunization with OMVs alone could significantly reduce the lesions following a G. anatis infection. A second study was carried out to characterize the dose-response (0.25, 2.5 and 25 µg) relationship of G. anatis OMVs as immunogens, showing that 2.5 μg of OMVs represent the optimal dose to elicit protection in the immunized animals after a similar challenge. Additionally, administration of ≥2.5 μg of G. anatis OMVs induced specific IgY titers and possibly vertical transfer of immunity.

Potential and safety tests of egg drop syndrome candidate vaccine from Medan isolate, Indonesia

Aim:

The study was aimed to prepare and examine the potential and safety concerns of egg drop syndrome (EDS) vaccine candidate seed. The potential and safety trials of EDS Medan isolate vaccine need to be done before commercial scale of EDS vaccines are made.

Materials and Methods:

The safety test of EDS candidate vaccine was tested on 4-week-old specified pathogen-free chickens in an experimentally isolated enclosure.

Results:

The result of the safety test obtained 2^7.3 hemagglutination inhibition (HI) unit of geometric mean titer antibody post-vaccination. However, the potency test of the EDS candidate vaccine was conducted on 17-week-old laying hens. Test results of the EDS potency vaccine in layer obtained antibody titer increased in every week of blood taking with average titer of antibody: Before vaccinated was 2^2.9 HI unit, 1 week after vaccination was 2^3.7 HI unit, 2 weeks post-vaccination was 2⁵ HI unit, and 3 weeks after vaccination was 2^7.3 HI units. In contrast, decreasing trend was observed in control group (unvaccinated chicken).

Conclusion:

Serologically, the seed vaccine of EDS virus isolates from Medan was able to produce protective antibody titers starting in the 2^nd and 3^rd weeks post-vaccination.

Recombinant infectious laryngotracheitis virus expressing Newcastle disease virus F protein protects chickens against infectious laryngotracheitis virus and Newcastle disease virus challenge

In this study, we isolated and identified an infectious laryngotracheitis virus (ILTV) that was naturally avirulent in specific pathogen-free (SPF) chickens, with the aim of developing a more efficacious vaccine against ILTV and Newcastle disease virus (NDV). We constructed a US9-deleted ILTV mutant based on this avirulent ILTV, and then constructed a recombinant ILTV (designated ILTV-ΔUS9-F) expressing the fusion protein (F) of the genotype VII NDV based on the US9-deleted ILTV mutant. Expression of the F protein in ILTV-ΔUS9-F-infected cells was confirmed by indirect immunofluorescence assay and western blotting. The inserted F gene was stably expressed in ILTV-ΔUS9-F. The growth kinetics of ILTV-ΔUS9-F were comparable to those of the wild-type ILTV strain. Vaccination of SPF chickens with ILTV-ΔUS9-F produced no clinical signs but did induce low levels of NDV-specific enzyme-linked immunosorbent assay and neutralizing antibodies. A single vaccination with 10⁴ plaque-forming units (PFU) of ILTV-ΔUS9-F provided good protection against both genotype VII and IX NDVs based on clinical signs, similar to the protection provided by the commercial live La Sota vaccine. Notably, ILTV-ΔUS9-F limited the replication and shedding of genotype VII NDV from oropharyngeal swabs more efficiently than the La Sota vaccine. In addition, vaccination with lower doses (10³ and 10² PFU) of ILTV-ΔUS9-F also provided sufficient clinical protection. These results indicated that ILTV-ΔUS9-F may be a bivalent vaccine candidate against both ILTV and NDV.

Maternal antibody inhibition of recombinant Newcastle disease virus vectored vaccine in a primary or booster avian influenza vaccination program of broiler chickens

Maternally-derived antibodies (MDA) provide early protection from disease, but may interfere with active immunity in young chicks. In highly pathogenic avian influenza virus (HPAIV)-enzootic countries, broiler chickens typically have MDA to Newcastle disease virus (NDV) and H5 HPAIV, and their impact on active immunity from recombinant vectored vaccines is unclear. We assessed the effectiveness of a spray-applied recombinant NDV vaccine with H5 AIV insert (rNDV-H5) and a recombinant turkey herpesvirus (HVT) vaccine with H5 AIV insert (rHVT-H5) in commercial broilers with MDA to NDV alone (MDA:AIV^-NDV⁺) or to NDV plus AIV (MDA:AIV⁺NDV⁺) to provide protection against homologous HPAIV challenge. In Experiment 1, chicks were spray-vaccinated with rNDV-H5 at 3 weeks (3w) and challenged at 5 weeks (5w). All sham-vaccinated progeny lacked AIV antibodies and died following challenge. In rNDV-H5 vaccine groups, AIV and NDV MDA had completely declined to non-detectable levels by vaccination, enabling rNDV-H5 spray vaccine to elicit a protective AIV antibody response by 5w, with 70-78% survival and significant reduction of virus shedding compared to shams. In Experiment 2, progeny were vaccinated with rHVT-H5 and rNDV-H5 at 1 day (1d) or 3w and challenged at 5w. All sham-vaccinated progeny lacked AIV antibodies and died following challenge. In rHVT-H5(1d) vaccine groups, irrespective of rNDV-H5(3w) boost, AIV antibodies reached protective levels pre-challenge, as all progeny survived and virus shedding significantly decreased compared to shams. In contrast, rNDV-H5-vaccinated progeny had AIV and/or NDV MDA at the time of vaccination (1d and/or 3w) and failed to develop a protective immune response by 5w, resulting in 100% mortality after challenge. Our results demonstrate that MDA to AIV had minimal impact on the effectiveness of rHVT-H5, but MDA to AIV and/or NDV at the time of vaccination can prevent development of protective immunity from a primary or booster rNDV-H5 vaccine.

Persistence of maternal antibodies to influenza A virus among captive mallards (Anas platyrhynchos)

Wild waterfowl are maintenance hosts of most influenza A virus (IAV) subtypes and are often the subjects of IAV surveillance and transmission models. While maternal antibodies have been detected in yolks and in nestlings for a variety of wild bird species and pathogens, the persistence of maternal antibodies to IAVs in mallard ducklings (Anas platyrhynchos) has not been previously investigated. Nonetheless, this information is important for a full understanding of IAV transmission dynamics because ducklings protected by maternal antibodies may not be susceptible to infection. In this study, we examined the transfer of IAV-specific maternal antibodies to ducklings. Blood samples were collected approximately every five days from ducklings hatched from hens previously infected with an H6 strain of IAV. Serum samples were tested for antibodies to IAV by an enzyme-linked immunosorbent assay. The median persistence of maternal antibodies in ducklings was 12.5 days (range: 4-33 days) post-hatch. The majority of ducklings (71%) had detectable maternal antibodies from 4 to 17 days post-hatch, while a small subset of individuals (29%) had detectable maternal antibodies for up to 21-33 days post-hatch. Antibody concentrations in hens near the time of egg laying were correlated with maternal antibody concentrations in the initial blood sample collected from ducklings (0-4 days post-hatch). Knowledge of the duration of maternal antibodies in ducklings will aid in the interpretation of IAV serological surveillance results and in the modeling of IAV transmission dynamics in waterfowl.

Recent advances in viral vectors in veterinary vaccinology

Viral vectored vaccines, particularly using vectors such as adenovirus, herpesvirus and poxviruses, are used widely in veterinary medicine, where this technology has been adopted much more quickly than in human medicine. There are now a large number of programmes to develop viral vector vaccine platforms for humans and very similar or identical vectors are being developed for veterinary medicine. The shared experiences of developing these new vaccine platforms across the two disciplines is accelerating progress, a striking example of the value of a 'One Health' approach. In particular, there is growing use of adenoviruses, either replicating or replication-incompetent, to create new vaccines for use in livestock or companion animals. Live replicating avian herpesvirus vectors are increasingly used as vaccines against poultry diseases.

Recombinant Avian Paramyxovirus Serotypes 2, 6, and 10 as Vaccine Vectors for Highly Pathogenic Avian Influenza in Chickens with Antibodies Against Newcastle Disease Virus

Recombinant Newcastle disease virus (rNDV) expressing the hemagglutinin of highly pathogenic avian influenza virus (HPAIV HA) induces protective immunity against HPAIV in chickens. However, the efficacy of rNDV vectors is hampered when chickens are pre-immune to NDV, and most commercial chickens are routinely vaccinated against NDV. We recently showed that avian paramyxovirus serotypes 2, 6, and 10 (APMV-2, APMV-6, and APMV-10), which belong to the same genus as NDV, have low cross-reactivity with anti-NDV antisera. Here, we used reverse genetics to generate recombinant APMV-2, APMV-6, and APMV-10 (rAPMV-2/HA, rAPMV-6/HA, and rAPMV-10/HA) that expressed an HA protein derived of subtype H5N1 HPAIV, A/chicken/Yamaguchi/7/2004. Chickens pre-immunized against NDV (age, 7 wk) were vaccinated with rAPMV/HAs; 14 days after vaccination, chickens were challenged with a lethal dose of HPAIV. Immunization of chickens pre-immunized against NDV with rAPMV-2/HA, rAPMV-6/HA, or rAPMV-10/HA protected 50%, 50%, and 25%, respectively, in groups of chickens given an rAPMV/HA with 106 median embryo infectious dose (EID₅₀) or 50%, 50%, and 90%, respectively, in those with 10⁷ EID₅₀; in contrast, rNDV/HA protected none of the chicken vaccinated with 10⁶ EID₅₀ and induced only partial protection even with 10⁷ EID_50. Therefore, the presence of anti-NDV antibodies did not hamper the efficacy of rAPMV-2/HA, rAPMV-6/HA, or rAPMV-10/HA. These results suggest that rAPMV-2, rAPMV-6, and rAPMV-10 are potential vaccine vectors, especially for commercial chickens, which are routinely vaccinated against NDV.

Stronger Interference of Avian Influenza Virus-Specific Than Newcastle Disease Virus-Specific Maternally Derived Antibodies with a Recombinant NDV-H5 Vaccine

Maternally derived antibodies (MDA) are known to provide early protection from disease but also to interfere with vaccination efficacy of young chicks. This interference phenomenon is well described in the literature for viral diseases such as infectious bursal disease, Newcastle disease (ND), and avian influenza (AI). The goal of this work was to investigate the impact of H5 MDA and/or ND virus (NDV) MDA on the vaccine efficacy of a recombinant NDV-H5-vectored vaccine (rNDV-H5) against two antigenically divergent highly pathogenic AI (HPAI) H5N1 challenges. In chickens with both H5 and NDV MDA, a strong interference was observed with reduced clinical protection when compared to vaccinated specific-pathogen-free (SPF) chickens. In contrast, in chickens from commercial suppliers with NDV MDA only, a beneficial impact on the vaccine efficacy was observed with full protection and reduced viral excretion in comparison with rNDV-H5-vaccinated SPF chickens. To distinguish between the respective effects of the H5 and NDV MDA, an SPF model where passive immunity had been artificially induced by inoculations of H5 and NDV hyperimmunized polysera, respectively, was used. In the presence of H5 artificial MDA, a strong interference reflected by a reduction in vaccine protection was demonstrated whereas no interference and even an enhancing protective effect was confirmed in presence of NDV MDA. The present work suggests that H5 and NDV MDA interact differently with the rNDV-H5 vaccine with different consequences on its efficacy, the mechanisms of which require further investigations.

Newcastle disease vaccines-A solved problem or a continuous challenge?

Newcastle disease (ND) has been defined by the World Organisation for Animal Health as infection of poultry with virulent strains of Newcastle disease virus (NDV). Lesions affecting the neurological, gastrointestinal, respiratory, and reproductive systems are most often observed. The control of ND must include strict biosecurity that prevents virulent NDV from contacting poultry, and also proper administration of efficacious vaccines. When administered correctly to healthy birds, ND vaccines formulated with NDV of low virulence or viral-vectored vaccines that express the NDV fusion protein are able to prevent clinical disease and mortality in chickens upon infection with virulent NDV. Live and inactivated vaccines have been widely used since the 1950's. Recombinant and antigenically matched vaccines have been adopted recently in some countries, and many other vaccine approaches have been only evaluated experimentally. Despite decades of research and development towards formulation of an optimal ND vaccine, improvements are still needed. Impediments to prevent outbreaks include uneven vaccine application when using mass administration techniques in larger commercial settings, the difficulties associated with vaccinating free-roaming, multi-age birds of village flocks, and difficulties maintaining the cold chain to preserve the thermo-labile antigens in the vaccines. Incomplete or improper immunization often results in the disease and death of poultry after infection with virulent NDV. Another cause of decreased vaccine efficacy is the existence of antibodies (including maternal) in birds, which can neutralize the vaccine and thereby reduce the effectiveness of ND vaccines. In this review, a historical perspective, summary of the current situation for ND and NDV strains, and a review of traditional and experimental ND vaccines are presented.

Recombinant viral-vectored vaccines for the control of avian influenza in poultry

Vaccination is a commonly used tool for the control of both low pathogenic and highly pathogenic avian influenza (AI) viruses. Traditionally, inactivated adjuvanted vaccines made from a low pathogenic field strain have been used for vaccination, but advances in molecular biology have allowed a number of different viral vectored vaccines, expressing the AI virus hemagglutinin (HA) gene, to be developed and licensed for use for control of AI. This review summarizes the licensed vector vaccines available for use in poultry. As a group, these vaccines can stimulate both a cellular and humoral immune response and, when antigenically well matched to the target AI strain, are effective at preventing clinical disease and reducing virus shedding if vaccinated birds do become infected. The vaccines can often be given to one-day old chicks in the hatchery, which can provide early protection and is a cost effective route of administration of the vaccine. All the licensed vectored vaccines, because they only express the HA gene, can potentially be used to differentiate vaccinated from vaccinated and infected birds, which is often referred to as a DIVA strategy. Although a potentially valuable tool for the surveillance of the virus in countries that vaccinate, the DIVA principle has currently not been applied. Concern remains that maternal antibody or pre-existing immunity to the vector or to the AI HA insert can suppress the immune response to the vaccine. The viral vectored vaccines appear to work well with a prime boost strategy where the vectored vaccine is given first and a different type of vaccine, often a killed adjuvanted vaccine is given two or three weeks later.

Recombinant NDV expressing cytokines or fliC confers a quick immune response against NDV challenge and resistance to maternal antibody

Currently, there are two major bottleneck problems which seriously affect prevention of the Newcastle disease (ND): interference of maternal antibody on NDV vaccination and slow production of neutralization antibody. To overcome these problems, in present study, four rNDV vaccine strains expressing bio-adjuvants chIL2, chIL15, chGM-CSF or fliC gene were constructed and rescued using reverse genetics approach. The HI antibody titers of SPF birds immunized with rNDV reached to 5.5log2, 4.7log2, 6.5log2 and 5.8log2, respectively at the 8th day post immunization, while the antibody titers of the parental virus and control were 3.3log2 and 1log2, respectively. The immunized chickens were challenged by 10⁴ELD₅₀ dose of the virulent NDV BJ strains at the 7th day post immunization. The protection rate of the four rNDVs bio-adjuvant groups was 100%, while the protection rate of the parental group was 80%. We also examined the anti-maternal antibody activity of these adjuvant vaccines by detection HI titer after vaccination of chickens with high (8.4log2) or low (5log2) maternal antibody levels. In chicken flock with higher maternal antibody, parental strain could not resist the influence of the maternal antibody and induce any notable change of HI antibody kinetics. However, both rClon30-chGM-CSF and rClon30-flic were able to resist the influence of the maternal antibody and maintained the HI antibody above the protection level during the 14day's experiment. In chicken flock with lower maternal antibody, the parental rclone30 strain could not induce HI titer to the protection level until the 14th day, but both rClon30-GM-CSF and clone30-fliC raised the HI antibody to above the protection level at the 7th day post vaccination.

Induction of non-specific suppression in chicks by specific combination of maternal antibody and related antigen

Specific immune suppression in newly hatched chicks induced by specific maternal antibodies has been reported. Laying hens were immunized with dinitrophenyl-keyhole limpet hemocyanin (DNP-KLH). Purified maternal anti-DNP and non-specific immunoglobulin (Ig) Y antibodies were transferred by yolk sac inoculation to newly hatched chicks, and then, they were immunized with an optimum immunogenic dose of DNP-KLH at 1 and 4 weeks of age. Concentrations of anti-DNP antibodies in serum samples of these chicks were measured by using Enzyme-linked immunosorbent assay (ELISA). Proportions of T-cell subsets in peripheral blood of these chicks were also measured by flow cytometric analysis at 5 weeks of age (one week after the second immunization). Suppression of anti-DNP antibody response and down-regulation of CD3⁺CD4⁺ cells were observed in the chicks received high dose of maternal anti-DNP antibodies and immunized with DNP-KLH. On the other hand, normal anti-DNP antibody response and normal proportion of CD3⁺CD4⁺ cells were observed in the chicks received high dose of non-specific IgY antibodies and immunized with DNP-KLH. Furthermore, when chicks received high dose of maternal anti-DNP antibodies and immunized with DNP-KLH at 1 and 4 weeks of age and then with rabbit serum albumin (RSA) at 5 and 8 weeks of age, their primary anti-RSA response was also significantly suppressed. We indicate here that specific maternal antibodies can affect both B and T cell responses and induce non-specific suppression against different antigens. However, this non-specific suppression does not continue for a long time.

Progress and challenges toward the development of vaccines against avian infectious bronchitis

Avian infectious bronchitis (IB) is a widely distributed poultry disease that has huge economic impact on poultry industry. The continuous emergence of new IBV genotypes and lack of cross protection among different IBV genotypes have been an important challenge. Although live attenuated IB vaccines remarkably induce potent immune response, the potential risk of reversion to virulence, neutralization by the maternal antibodies, and recombination and mutation events are important concern on their usage. On the other hand, inactivated vaccines induce a weaker immune response and may require multiple dosing and/or the use of adjuvants that probably have potential safety risks and increased economic burdens. Consequently, alternative IB vaccines are widely sought. Recent advances in recombinant DNA technology have resulted in experimental IB vaccines that show promise in antibody and T-cells responses, comparable to live attenuated vaccines. Recombinant DNA vaccines have also been enhanced to target multiple serotypes and their efficacy has been improved using delivery vectors, nanoadjuvants, and in ovo vaccination approaches. Although most recombinant IB DNA vaccines are yet to be licensed, it is expected that these types of vaccines may hold sway as future vaccines for inducing a cross protection against multiple IBV serotypes.

Immunogenicity and efficacy of fowlpox-vectored and inactivated avian influenza vaccines alone or in a prime-boost schedule in chickens with maternal antibodies

Inactivated and fowlpox virus (FP)-vectored vaccines have been used to control H5 avian influenza (AI) in poultry. In H5 AI endemic countries, breeder flocks are vaccinated and therefore, maternally-derived antibodies (MDA) are transferred to their progeny. Results of three immunogenicity and one efficacy studies performed in birds with or without MDA indicated that the immunogenicity of an inactivated vaccine based on a H5N9 AI isolate (inH5N9) was severely impaired in chicks hatched from inH5N9-vaccinated breeders. This MDA interference was lower when breeders received only one administration of the same vaccine and could be overcome by priming the chicks at day-of-age with a live recombinant FP-vectored vaccine with H5 avian influenza gene insert (FP-AI). The interference of anti-FP MDA was of lower intensity than the interference of anti-AI MDA. The highest interference observed on the prime-boost immunogenicity was in chicks hatched from breeders vaccinated with the same prime-boost scheme. The level of protection against an antigenic variant H5N1 highly pathogenic AI isolate from Indonesia against which the FP-AI or inH5N9 alone was poorly protective could be circumvented by the prime-boost regimen in birds with either FP or AI MDA. Thus, the immunogenicity of vaccines in young chicks with MDA depends on the vaccination scheme and the type of vaccine used in their parent flocks. The heterologous prime-boost in birds with MDA may at least partially overcome MDA interference on inactivated vaccine.

Practical aspects of vaccination of poultry against avian influenza virus

Although little has changed in vaccine technology for avian influenza virus (AIV) in the past 20 years, the approach to vaccination of poultry (chickens, turkeys and ducks) for avian influenza has evolved as highly pathogenic AIV has become endemic in several regions of the world. Vaccination for low pathogenicity AIV is also becoming routine in regions where there is a high level of field challenge. In contrast, some countries will not use vaccination at all and some will only use it on an emergency basis during eradication efforts (i.e. stamping-out). There are pros and cons to each approach and, since every outbreak situation is different, no one method will work equally well in all situations. Numerous practical aspects must be considered when developing an AIV control program with vaccination as a component, such as: (1) the goals of vaccination must be defined; (2) the population to be vaccinated must be clearly identified; (3) there must be a plan to obtain and administer good quality vaccine in a timely manner and to achieve adequate coverage with the available resources; (4) risk factors for vaccine failure should be mitigated as much as possible; and, most importantly, (5) biosecurity must be maintained as much as possible, if not enhanced, during the vaccination period.