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

Protection conferred by an H5 DNA vaccine against highly pathogenic avian influenza in chickens: The effect of vaccination schedules

H5 highly pathogenic avian influenza (HPAI) viruses of the Asian lineage (A/goose/Guangdong/1/96) belonging to clade 2.3.4.4 have spread worldwide through wild bird migration in two major waves: in 2014/2015 (clade 2.3.4.4c), and since 2016 up to now (clade 2.3.4.4b). Due to the increasing risk of these H5 HPAI viruses to establish and persist in the wild bird population, implementing vaccination in certain sensitive areas could be a complementary measure to the disease control strategies already applied. In this study, the efficacy of a novel DNA vaccine, encoding a H5 gene (A/gyrfalcon/Washington/41088-6/2014 strain) of clade 2.3.4.4c was evaluated in specific pathogen-free (SPF) white leghorn chickens against a homologous and heterologous H5 HPAI viruses. A single vaccination at 2 weeks of age (1 dose), and a vaccination at 2 weeks of age, boosted at 4 weeks (2 doses), with or without adjuvant were characterized. The groups that received 1 dose with or without adjuvant as well as 2 doses with adjuvant demonstrated full clinical protection and a significant or complete reduction of viral shedding against homologous challenge at 6 and 25 weeks of age. The heterologous clade 2.3.4.4b challenge of 6-week-old chickens vaccinated with 2 doses with or without adjuvant showed similar results, indicating good cross-protection induced by the DNA vaccine. Long lasting humoral immunity was observed in vaccinated chickens up to 18 or 25 weeks of age, depending on the vaccination schedule. The analysis of viral transmission after homologous challenge showed that sentinels vaccinated with 2 doses with adjuvant were fully protected against mortality with no excretion detected. This study of H5 DNA vaccine efficacy confirmed the important role that this type of so-called third-generation vaccine could play in the fight against H5 HPAI viruses.

Efficacy of an inactivated influenza vaccine adjuvanted with Toll-like receptor ligands against transmission of H9N2 avian influenza virus in chickens

Avian influenza viruses (AIV), including the H9N2 subtype, pose a major threat to the poultry industry as well as to human health. Although vaccination provides a protective control measure, its effect on transmission remains uncertain in chickens. The objective of the present study was to investigate the efficacy of beta-propiolactone (BPL) whole inactivated H9N2 virus (WIV) vaccine either alone or in combination with CpG ODN 2007 (CpG), poly(I:C) or AddaVax™ (ADD) to prevent H9N2 AIV transmission in chickens. The seeder chickens (trial 1) and recipient chickens (trial 2) were vaccinated twice with different vaccine formulations. Ten days after secondary vaccination, seeder chickens were infected with H9N2 AIV (trial 1) and co-housed with healthy recipient chickens. In trial 2, the recipient chickens were vaccinated and then exposed to H9N2 AIV-infected seeder chickens. Our results demonstrated that BPL+ CpG and BPL+ poly(I:C) treated chickens exhibited reduced oral and cloacal shedding in both trials post-exposure (PE). The number of H9N2 AIV+ recipient chickens in the BPL+ CpG group (trial 1) was lower than in other vaccinated groups, and the reduction was higher in BPL+ CpG recipient chickens in trial 2. BPL+ CpG vaccinated chickens demonstrated enhanced systemic antibody responses with high IgM and IgY titers with higher rates of seroprotection by day 21 post-primary vaccination (ppv). Additionally, the induction of IFN-γ expression and production was higher in the BPL+ CpG treated chickens. Interleukin (IL)- 2 expression was upregulated in both BPL+ CpG and BPL+ poly(I:C) groups at 12 and 24 hr post-stimulation.

Advances in Poultry Vaccines: Leveraging Biotechnology for Improving Vaccine Development, Stability, and Delivery

With the rapidly increasing demand for poultry products and the current challenges facing the poultry industry, the application of biotechnology to enhance poultry production has gained growing significance. Biotechnology encompasses all forms of technology that can be harnessed to improve poultry health and production efficiency. Notably, biotechnology-based approaches have fueled rapid advances in biological research, including (a) genetic manipulation in poultry breeding to improve the growth and egg production traits and disease resistance, (b) rapid identification of infectious agents using DNA-based approaches, (c) inclusion of natural and synthetic feed additives to poultry diets to enhance their nutritional value and maximize feed utilization by birds, and (d) production of biological products such as vaccines and various types of immunostimulants to increase the defensive activity of the immune system against pathogenic infection. Indeed, managing both existing and newly emerging infectious diseases presents a challenge for poultry production. However, recent strides in vaccine technology are demonstrating significant promise for disease prevention and control. This review focuses on the evolving applications of biotechnology aimed at enhancing vaccine immunogenicity, efficacy, stability, and delivery.

Vaccination Technology in Poultry: Principles of Vaccine Administration

Poultry vaccines are very important tools for disease prevention and may be administered collectively by drinking water or spray or individually by injection or oculonasal drop, whereas inactivated vaccines are administered by injection only. Poultry vaccines are increasingly delivered at the hatchery to day-old chicks or in ovo, because mass vaccination is much more efficiently implemented and controlled at the hatchery than on the farm. Mass administration on the farm by drinking water or spray requires strict compliance with guidelines regarding water quality, preparation of vaccines, and application, so as to cover the whole flock. Vaccination at the hatchery uses integrated machines to deliver vaccines to day-old chicks or, increasingly, in ovo at transfer from setters to hatchers. Regardless of the route and technology, a high quality of monitoring is critically important to maintain strict compliance and best practices from the vaccine vial to the bird, to guarantee efficient administration and intake of the vaccine by the whole flock and to secure the integrity of the vaccine itself. Major recent technical innovations in poultry vaccination covering both biology and technology open a very exciting era.

Self-Assembled Virus-Like Particle Vaccines via Fluorophilic Interactions Enable Infection Mimicry and Immune Protection

Influenza epidemics persistently threaten global health. Vaccines based on virus-like particles (VLPs), which resemble the native conformation of viruses, have emerged as vaccine candidates. However, the production of VLPs via genetic engineering remains constrained by challenges such as low yields, high costs, and being time consuming. In this study, a novel VLP platform is developed that could mimic infection and confer influenza protection through fluorination-driven self-assembly. The VLPs closely mimick the key steps in viral infection including dendritic cell (DC) attachment and pH-responsive endo-lysosomal escape, which enhances DC maturation and antigen cross-presentation. It is also observed that the VLPs migrate from the injection site to the draining lymph nodes efficiently. Immunization with VLPs triggers both Th1 and Th2 cellular responses, thereby inducing an improved CD8+ T cell response along with strong antigen-specific antibody responses. In several infected mouse models, VLP vaccines ameliorate weight loss, lung virus titers, pulmonary pathologies, and confer full protection against H1N1, H6N2, H9N2, and mixed influenza viruses. Therefore, the results support the potential of VLPs as an effective influenza vaccine with improved immune potency against infection. A methodology to generate VLPs based on fluorophilic interactions, which can be a general approach for development of pathogenic VLPs, is reported.

Prediction of highly pathogenic avian influenza vaccine efficacy in chickens by comparison of in vitro and in vivo data: A meta-analysis and systematic review

Vaccines for avian influenza (AI) can protect poultry against disease, mortality, and virus transmission. Numerous factors, including: vaccine platform, immunogenicity, and relatedness to the field strain, are known to be important to achieving optimal AI vaccine efficacy. To better understand how these factors contribute to vaccine protection, a systematic meta-analysis was conducted to evaluate efficacy data for vaccines in chickens challenged with highly pathogenic (HP) AI. Data from a total of 120 individual trials from 25 publications were selected and evaluated. Two vaccine criteria were evaluated for their effects on two metrics of protection. The vaccine criteria were: 1) the relatedness of the vaccine antigen and challenge strain in the hemagglutinin 1 domain (HA1) protein sequence; 2) vaccine-induced antibody titers to the challenge virus (VIAC). The metrics of protection were: A) survival of vaccinated chickens vs unvaccinated controls; and B) reduction in oral virus-shedding by vaccinated vs unvaccinated controls 2-4 days post challenge. Three vaccine platforms were evaluated: oil-adjuvanted inactivated whole AI virus, recombinant herpes virus of turkeys (rHVT) vectored, and a non-replicating alpha-virus vectored RNA particle (RP) vaccine. Higher VIAC correlated with greater reduction of virus-shed and vaccine efficacy by all vaccine platforms. Both higher HA1 relatedness and higher VIAC using challenge virus as antigen correlated with better survival by inactivated vaccines and rHVT-vectored vaccines. However, rHVT-vectored and RP based vaccines were more tolerant of variation in the HA1; the relatedness of the HA1 of the vaccine and challenge virus did not significantly correlate with survival with rHVT-vectored vaccines. Protection was achieved with the lowest aa similarity for which there was data, 90-93 % for rHVT vaccines and 88 % for the RP vaccine.

Multiple Vaccines and Strategies for Pandemic Preparedness of Avian Influenza Virus

Avian influenza viruses (AIV) are a continuous cause of concern due to their pandemic potential and devasting effects on poultry, birds, and human health. The low pathogenic avian influenza virus has the potential to evolve into a highly pathogenic avian influenza virus, resulting in its rapid spread and significant outbreaks in poultry. Over the years, a wide array of traditional and novel strategies has been implemented to prevent the transmission of AIV in poultry. Mass vaccination is still an economical and effective approach to establish immune protection against clinical virus infection. At present, some AIV vaccines have been licensed for large-scale production and use in the poultry industry; however, other new types of AIV vaccines are currently under research and development. In this review, we assess the recent progress surrounding the various types of AIV vaccines, which are based on the classical and next-generation platforms. Additionally, the delivery systems for nucleic acid vaccines are discussed, since these vaccines have attracted significant attention following their significant role in the fight against COVID-19. We also provide a general introduction to the dendritic targeting strategy, which can be used to enhance the immune efficiency of AIV vaccines. This review may be beneficial for the avian influenza research community, providing ideas for the design and development of new AIV vaccines.

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.

Vaccines against Major Poultry Viral Diseases: Strategies to Improve the Breadth and Protective Efficacy

The poultry industry is the largest source of meat and eggs for human consumption worldwide. However, viral outbreaks in farmed stock are a common occurrence and a major source of concern for the industry. Mortality and morbidity resulting from an outbreak can cause significant economic losses with subsequent detrimental impacts on the global food supply chain. Mass vaccination is one of the main strategies for controlling and preventing viral infection in poultry. The development of broadly protective vaccines against avian viral diseases will alleviate selection pressure on field virus strains and simplify vaccination regimens for commercial farms with overall savings in husbandry costs. With the increasing number of emerging and re-emerging viral infectious diseases in the poultry industry, there is an urgent need to understand the strategies for broadening the protective efficacy of the vaccines against distinct viral strains. The current review provides an overview of viral vaccines and vaccination regimens available for common avian viral infections, and strategies for developing safer and more efficacious viral vaccines for poultry.

Characterization of Immune Response towards Generation of Universal Anti-HA-Stalk Antibodies after Immunization of Broiler Hens with Triple H5N1/NA-HA-M1 VLPs

(1) Background: Avian influenza viruses (AIVs) promptly evade preexisting immunity by constantly altering the immunodominant neutralizing antibody epitopes (antigenic drift) or by procuring new envelope serotypes (antigenic shift). As a consequence, the majority of antibodies elicited by infection or vaccination protect only against closely related strains. The immunodominance of the globular head of the main glycoprotein has been shown to mask the immunogenicity of the conserved regions located within the hemagglutinin (HA) protein. It has been shown that the broadly neutralizing universal antibodies recognize the HA2 domain in headless hemagglutinin (HA-stalk). Therefore, the HA-stalk is a highly conserved antigen, which makes it a good candidate to be used in universal vaccine development against AIVs. (2) Methods: Sf9 insect cells were used to produce triple H5N1/NA-HA-M1 influenza virus-like particles (VLPs) via co-expression of neuraminidase, hemagglutinin and matrix proteins from a tricistronic expression cassette. Purified influenza VLPs were used to immunize broiler hens. An in-depth characterization of the immune response was performed with an emphasis on the pool of elicited universal antibodies. (3) Results: Our findings suggest, that after vaccination with triple H5N1/NA-HA-M1 VLPs, hens generate a pool of broad-spectrum universal anti-HA-stalk antibodies. Furthermore, these universal antibodies are able to recognize the mammalian-derived HA-stalk recombinant proteins from homologous H5N1 and heterologous H7N9 AIVs as well as from the heterosubtypic human H1N1 influenza strain. (4) Conclusions: Our findings may suggest that highly pathogenic avian influenza H5 HA protein contain functional epitopes that are attractive targets for the generation of broad-spectrum antibodies against AIVs in their native hosts.

Strategies for enhancing immunity against avian influenza virus in chickens: A review

Poultry infection with avian influenza viruses (AIV) is a continuous source of concern for poultry production and human health. Uncontrolled infection and transmission of AIV in poultry increases the potential for viral mutation and reassortment, possibly resulting in the emergence of zoonotic viruses. To this end, implementing strategies to disrupt the transmission of AIVs in poultry, including a wide array of traditional and novel methods, is much needed. Vaccination of poultry is a targeted approach to reduce clinical signs and shedding in infected birds. Strategies aimed at enhancing the effectiveness of AIV vaccines are multi-pronged and include methods directed towards eliciting immune responses in poultry. Strategies include producing vaccines of greater immunogenicity via vaccine type and adjuvant application and increasing bird responsiveness to vaccines by modification of the gastrointestinal tract (GIT) microbiome and dietary interventions. This review provides an in-depth discussion of recent findings surrounding novel AIV vaccines for poultry, including reverse genetics vaccines, vectors, protein vaccines and virus like particles, highlighting their experimental efficacy among other factors such as safety and potential for use in the field. In addition to the type of vaccine employed, vaccine adjuvants also provide an effective way to enhance AIV vaccine efficacy, therefore, research on different types of vaccine adjuvants and vaccine adjuvant delivery strategies is discussed. Finally, the poultry gastrointestinal microbiome is emerging as an important factor in the effectiveness of prophylactic treatments. In this regard, current findings on the effects of the chicken GIT microbiome on AIV vaccine efficacy are summarized here.

Review of Poultry Recombinant Vector Vaccines

The control of poultry diseases has relied heavily on the use of many live and inactivated vaccines. However, over the last 30 yr, recombinant DNA technology has been used to generate many novel poultry vaccines. Fowlpox virus and turkey herpesvirus are the two main vectors currently used to construct recombinant vaccines for poultry. With the use of these two vectors, more than 15 recombinant viral vector vaccines against Newcastle disease, infectious laryngotracheitis, infectious bursal disease, avian influenza, and Mycoplasma gallisepticum have been developed and are commercially available. This review focuses on current knowledge about the safety and efficacy of recombinant viral vectored vaccines and the mechanisms by which they facilitate the control of multiple diseases. Additionally, the development of new recombinant vaccines with novel vectors will be briefly discussed.

H5 cleavage-site peptide vaccine protects chickens from lethal infection by highly pathogenic H5 avian influenza viruses

Highly pathogenic H5Nx avian influenza viruses constantly threaten the poultry industry and humans and have pandemic potential. These viruses continuously evolve, requiring a universal vaccine to protect chickens from members of diverse clades. The purpose of this study was to develop an H5 cleavage-site peptide vaccine containing polybasic amino acids (RRRK) to completely protect chickens from H5N6, H5N8, and H5N1 avian influenza viruses. Chickens were immunized with various doses of a keyhole limpet hemocyanin (KLH)-conjugated H5 cleavage-site peptide vaccine containing RRRK. The effect of RRRK was evaluated by comparing the survival rates of chickens immunized with vaccines either containing or lacking RRRK. The ability of the RRRK-containing vaccine to confer long-term protective immunity was also assessed. We found that protection was dependent on the number of antigens in the vaccine containing RRRK. Chickens immunized intramuscularly with two doses of 5 μg of the vaccine containing RRRK were completely protected, but those immunized with fewer than two doses of 3 or 1 μg were not protected. Chickens immunized with the vaccine lacking RRRK were not protected, suggesting the importance of the polybasic amino acids in conferring immunity. Our results suggest that conserved H5 cleavage-site peptides with polybasic amino acids may be a potential universal vaccine to protect chickens from various emerging clades of H5Nx avian influenza viruses.

Risk Factors for Positivity to Shiga Toxin-Producing Escherichia coli and Salmonella enterica in Backyard Production Systems Animals from Metropolitana Region, Chile: A Threat to Public Health?

In the Metropolitana region of Chile there are 3836 backyard production systems (BPS), characterized as small-scale systems. They act as a source of zoonotic pathogens, such as Salmonella enterica and Shiga toxin-producing Escherichia coli (STEC), whose prevalence in BPS has not been fully described. The objective of this study was to determine the positivity for both agents in BPS and to establish the risk factors related to their presence. In each BPS, an epidemiological survey was undertaken, and stool samples were collected to detect these pathogens via bacteriological culture and conventional PCR techniques. Subsequently, multivariable logistic regression models were applied to establish the risk factors associated with their presence. BPS positivity rates of 11.76% for STEC and 4.7% for S. enterica were observed. The systems showed poor welfare standards and a lack of biosecurity measures. The risk factor analysis concluded that the Gini–Simpson index (p = 0.030; OR = 1.717) and the presence of neighboring intensive poultry or swine production systems (p = 0.019; OR = 20.645) act as factors that increased the risk of positivity with respect to STEC. In the case of S. enterica, exchanging embryonated eggs (p = 0.021; OR = 39) and the presence of debeaked chickens (p = 0.001; OR = 156) were determined as factors that increased the risk of positivity for this agent. For positivity with respect to both pathogens, the Gini–Simpson index (p = 0.030; OR = 1.544) and being INDAP/PRODESAL users (p = 0.023; OR = 15.026) were determined as factors that increased the risk, whereas the type of confinement (p = 0.002; OR = 0.019) decreased it. Epidemiological surveillance of these neglected populations is lacking, highlighting the fact that STEC and S. enterica maintenance on BPS represents a potential threat to public health.

Use of feline herpesvirus as a vaccine vector offers alternative applications for feline health

Herpesviruses are attractive vaccine vector candidates due to their large double stranded DNA genome and latency characteristics. Within the scope of veterinary vaccines, herpesvirus-vectored vaccines have been well studied and commercially available vectored vaccines are used to help prevent diseases in different animal species. Felid alphaherpesvirus 1 (FHV-1) has been characterised as a vector candidate to protect against a range of feline pathogens. In this review we highlight the methods used to construct FHV-1 based vaccines and their outcomes, while also proposing alternative uses for FHV-1 as a viral vector.

Advances in Development and Application of Influenza Vaccines

Influenza A virus is one of the most important zoonotic pathogens that can cause severe symptoms and has the potential to cause high number of deaths and great economic loss. Vaccination is still the best option to prevent influenza virus infection. Different types of influenza vaccines, including live attenuated virus vaccines, inactivated whole virus vaccines, virosome vaccines, split-virion vaccines and subunit vaccines have been developed. However, they have several limitations, such as the relatively high manufacturing cost and long production time, moderate efficacy of some of the vaccines in certain populations, and lack of cross-reactivity. These are some of the problems that need to be solved. Here, we summarized recent advances in the development and application of different types of influenza vaccines, including the recent development of viral vectored influenza vaccines. We also described the construction of other vaccines that are based on recombinant influenza viruses as viral vectors. Information provided in this review article might lead to the development of safe and highly effective novel influenza vaccines.

The Expression of Hemagglutinin by a Recombinant Newcastle Disease Virus Causes Structural Changes and Alters Innate Immune Sensing

Recombinant Newcastle disease viruses (rNDV) have been used as bivalent vectors for vaccination against multiple economically important avian pathogens. NDV-vectored vaccines expressing the immunogenic H5 hemagglutinin (rNDV-H5) are considered attractive candidates to protect poultry from both highly pathogenic avian influenza (HPAI) and Newcastle disease (ND). However, the impact of the insertion of a recombinant protein, such as H5, on the biological characteristics of the parental NDV strain has been little investigated to date. The present study compared a rNDV-H5 vaccine and its parental NDV LaSota strain in terms of their structural and functional characteristics, as well as their recognition by the innate immune sensors. Structural analysis of the rNDV-H5 demonstrated a decreased number of fusion (F) and a higher number of hemagglutinin-neuraminidase (HN) glycoproteins compared to NDV LaSota. These structural differences were accompanied by increased hemagglutinating and neuraminidase activities of rNDV-H5. During in vitro rNDV-H5 infection, increased mRNA expression of TLR3, TLR7, MDA5, and LGP2 was observed, suggesting that the recombinant virus is recognized differently by sensors of innate immunity when compared with the parental NDV LaSota. Given the growing interest in using NDV as a vector against human and animal diseases, these data highlight the importance of thoroughly understanding the recombinant vaccines’ structural organization, functional characteristics, and elicited immune responses.

High immune efficacy against different avian influenza H5N1 viruses due to oral administration of a Saccharomyces cerevisiae-based vaccine in chickens

A safe and effective vaccine is the best way to control large-scale highly pathogenic avian influenza virus (HPAI) A (H5N1) outbreaks. Saccharomyces cerevisiae (S. cerevisiae) is an ideal mucosal delivery vector for vaccine development, and we have previously shown that conventional administration of a S. cerevisiae-based vaccine (EBY100/pYD1-HA) via injection led to protection against the homologous H5N1 virus in a mouse model. Because the diameter of S. cerevisiae is approximately 10 μm, which results in a severe inflammation by injection route, therefore, oral administration is a more suitable approach for EBY100/pYD1-HA conferring protection in poultry. We extended our work by evaluating the immunogenicity and protective efficacy of oral vaccination with EBY100/pYD1-HA in the chicken model. Oral immunization with EBY100/pYD1-HA could induce robust serum IgG, mucosal IgA and cellular immune responses. Importantly, EBY100/pYD1-HA provided protection against challenges with a homologous and a heterologous H5N1 viruses. These findings suggest that EBY100/pYD1-HA, a promising H5N1 oral vaccine candidate, can avoid potential reassortment of other avian influenza viruses in oral administration of live virus vaccines and overcome the limitations of conventional injection routes. Importantly, this platform will be able to provide opportunities for broader applications in poultry during HPAI A (H5N1) outbreaks.

Identification of Efficacious Vaccines Against Contemporary North American H7 Avian Influenza Viruses

Five vaccines, including four inactivated, whole-virus water-in-oil adjuvanted vaccines and a commercial nonreplicating alphavirus-vectored RNA particle (RP) vaccine were evaluated in chickens for their ability to provide protection against challenge with a recent H7 highly pathogenic avian influenza virus (AIV) from the United States (A/turkey/IN/1403-1/2016 H7N8). One of the inactivated vaccines and the RP vaccine were prepared with A/turkey/IN/16-01571-6/2016 H7N8 low pathogenic AIV (LPAIV; TK/IN/16), which is identical to the challenge virus, except for the proteolytic cleavage site of the hemagglutinin protein. The remaining three inactivated vaccines were prepared with other North American H7 LPAIVs. The hemagglutination inhibition assay was used to evaluate the antigenic relationships among the vaccines and selected recent H7 AIV isolates. All five vaccines provided protection against mortality. The inactivated vaccines reduced virus shedding significantly at 2 and 4 days post challenge compared with sham-vaccinated chickens. In contrast, the RP vaccine did not significantly reduce virus shedding. The inactivated vaccine prepared with TK/IN/16 elicited the highest antibody responses, which suggests it is a strong candidate for use as an antigen for North American H7 AIVs. Antigenic distance calculations showed that the four inactivated vaccine strains and other recent North American H7 isolates are antigenically similar, which suggests that the vaccines evaluated here would be similar enough to provide protection to other North American H7 AIVs. If future H7 outbreaks in poultry warrant vaccination, the field strain can be rapidly evaluated with these antigens and, if adequately related, one of these characterized strains may be used.

Are current avian influenza vaccines a solution for smallholder poultry farmers?

Vaccination against highly pathogenic avian influenza (HPAI) viruses, along with other measures, was successful in eradicating AI in very few countries where the competence of national veterinary services or the geography and bird density have contributed favorably to the outcome.  The main constraints to an effective AI vaccination are vaccine composition matching field strains, reliable cold chain and logistics to target all poultry smallholders, constraints related to the availability of sufficient financial and human resources.  When not conducted properly, vaccination can also contribute to the emergence of new field viral strains, through genetic drifts of HPAI viruses.   While new technologies have improved the possibility to produce high quality vaccines matching field strains, recurrent issues like post-vaccination field surveillance and vaccination coverage continue to limit the relevance of AI vaccination in smallholder settings. A "game-changer" vaccine targeting smallholders should be universal to protect against all field viral strains and reduce significantly, if not totally eliminate, the need for costly post-vaccination surveillance.  The ease of administration of this vaccine (eye drop or one single injection) would further contribute to its relevance in the field.  These characteristics are considered essential for the product profile of an AI vaccine that can contribute in a meaningful way to the livelihoods of poultry smallholders.

Herpesvirus of turkey-vectored avian influenza vaccine offers cross-protection against antigenically drifted H5Nx highly pathogenic avian influenza virus strains

Among the different vaccines used to control highly pathogenic avian influenza, an HVT vector-based live recombinant avian influenza vaccine, expressing the haemagglutinin gene of an H5N1 HPAI virus, has been used by the poultry industry since 2012. The objective of the study presented in this paper was to test the efficacy of the commercially available HVT-based recombinant H5 vaccine against antigenically drifted H5N1, H5N8 and H5N2 HPAI virus circulating in Egypt recently. Groups of SPF chicks vaccinated at day-old with the HVT-based recombinant H5 vaccine were challenged, along with non-vaccinated controls, with 10⁶ EID₅₀ each of H5N1, H5N2 or H5N8 HPAI virus at 28 days of age. The birds were monitored for clinical protection and virus shedding during a 10-day postchallenge period. Clinical protection levels were 90%, 90% and 80% following challenge with the H5N1, H5N2 and H5N8 field isolates, respectively. Challenge virus shedding was significantly reduced in vaccinated groups, with up to 40%, 30% and 20% of non-shedders, and 3.8, 3.3 and 2.8 log₁₀ reduction in the amount of excreted virus following challenge with H5N1, H5N2 and H5N8 viruses, respectively. Analyses of the amino acid sequences of the HA proteins of challenge viruses and serological relatedness with the vaccine insert revealed significant antigenic divergences between the vaccine and the challenge viruses. These results provide further evidence of the potential of HVT-based recombinant H5 vaccine to provide cross-protection against antigenically drifted HPAI H5Nx viruses with strong control on virus shedding.

Contributions of HA1 and HA2 Subunits of Highly Pathogenic Avian Influenza Virus in Induction of Neutralizing Antibodies and Protection in Chickens

Highly pathogenic avian influenza virus (HPAIV) subtype H5N1 causes a devastating disease in poultry. Vaccination is an effective method of controlling avian influenza virus (AIV) infection in poultry. The hemagglutinin (HA) protein is the major determinant recognized by the immune system of the host. Cleavage of the HA precursor HA0 into HA1 and HA2 subunits is required for infectivity of the AIV. We evaluated the individual contributions of HA1 and HA2 subunits to the induction of HPAIV serum neutralizing antibodies and protective immunity in chickens. Using reverse genetics, recombinant Newcastle disease viruses (rNDVs) were generated, each expressing HA1, HA2, or HA protein of H5N1 HPAIV. Chickens were immunized with rNDVs expressing HA1, HA2, or HA. Immunization with HA induced high titers of serum neutralizing antibodies and prevented death following challenge. Immunization with HA1 or HA2 alone neither induced serum neutralizing antibodies nor prevented death following challenge. Our results suggest that interaction of HA1 and HA2 subunits is necessary for the display of epitopes on HA protein involved in the induction of neutralizing antibodies and protection. These epitopes are lost when the two subunits are separated. Therefore, vaccination with either a HA1 or HA2 subunit may not provide protection against HPAIV.

Exploring the Prospects of Engineered Newcastle Disease Virus in Modern Vaccinology

Many traditional vaccines have proven to be incapable of controlling newly emerging infectious diseases. They have also achieved limited success in the fight against a variety of human cancers. Thus, innovative vaccine strategies are highly needed to overcome the global burden of these diseases. Advances in molecular biology and reverse genetics have completely restructured the concept of vaccinology, leading to the emergence of state-of-the-art technologies for vaccine design, development and delivery. Among these modern vaccine technologies are the recombinant viral vectored vaccines, which are known for their incredible specificity in antigen delivery as well as the induction of robust immune responses in the vaccinated hosts. Although a number of viruses have been used as vaccine vectors, genetically engineered Newcastle disease virus (NDV) possesses some useful attributes that make it a preferable candidate for vectoring vaccine antigens. Here, we review the molecular biology of NDV and discuss the reverse genetics approaches used to engineer the virus into an efficient vaccine vector. We then discuss the prospects of the engineered virus as an efficient vehicle of vaccines against cancer and several infectious diseases of man and animals.

Virus-Like Particle Based Vaccine Provides High Level of Protection Against Homologous H5N8 HPAIV Challenge in Mule and Pekin Duck, Including Prevention of Transmission

The most recent pandemic clade of highly pathogenic avian influenza (HPAI) H5, clade 2.3.4.4, spread widely, with the involvement of wild birds, most importantly wild waterfowl, carrying the virus (even asymptomatically) from Asia to North America, Europe, and Africa. Domestic waterfowl being in regular contact with wild birds played a significant role in the H5Nx epizootics. Therefore, protection of domestic waterfowl from H5Nx avian influenza infection would likely cut the transmission chain of these viruses and greatly enhance efforts to control and prevent disease outbreak in other poultry and animal species, as well as infection of humans. The expectation for such a vaccine is not only to provide clinical protection, but also to control challenge virus transmission efficiently and ensure that the ability to differentiate infected from vaccinated animals is retained. A water-in-oil emulsion virus-like particle vaccine, containing homologous hemagglutinin antigen to the current European H5N8 field strains, has been developed to meet these requirements. The vaccine was tested in commercial Pekin and mule ducks by vaccinating them either once, at 3 wk of age, or twice (at 1 day and at 3 wk of age). Challenge was performed at 6 wk of age with a Hungarian HPAIV H5N8 isolate (2.3.4.4 Group B). Efficacy of vaccination was evaluated on the basis of clinical signs, amount of virus shedding, and transmission. Vaccination resulted in complete clinical protection and prevention of challenge virus transmission from the directly challenged vaccinated ducks to the vaccinated contact animals.

Efficacy of Two Licensed Avian Influenza H5 Vaccines Against Challenge with a 2015 U.S. H5N2 clade 2.3.4.4 Highly Pathogenic Avian Influenza Virus in Domestic Ducks

Highly pathogenic avian influenza (HPAI) clade 2.3.4.4 viruses from the H5 goose/Guangdong lineage caused a major outbreak in poultry in the United States in 2015. Although the outbreak was controlled, vaccines were considered as an alternative control method, and new vaccines were approved and purchased by the U.S. Department of Agriculture National Veterinary Stockpile for emergency use. In this study, we evaluated the efficacy of two of these vaccines in protecting Pekin ducks (Anas platyrhynchos var. domestica) against challenge with a H5N2 HPAI poultry isolate. A recombinant alphavirus-based vaccine and an inactivated adjuvanted reverse genetics vaccine, both expressing the hemagglutinin gene of a U.S. H5 clade 2.3.4.4 isolate (A/Gyrfalcon/Washington/41088-6/2014 H5N8), were used to immunize the ducks. The vaccines were given either as single vaccination at 2 days of age or in a prime-boost strategy at 2 and 15 days of age. At 32 days of age, all ducks were challenged with A/turkey/Minnesota/12582/15 H5N2 HPAI virus clade 2.3.4.4. All ducks from the nonvaccinated challenge control group became infected and shed virus; one duck in this group presented mild ataxia, and a second duck died. No mortality or clinical signs were observed in vaccinated and challenged ducks, with the exception of one duck presenting with mild ataxia. Both vaccines, regardless of the vaccination strategy used, were immunogenic in ducks and reduced or prevented virus shedding after challenge. In conclusion, good protection against H5Nx infection was achieved in ducks vaccinated with the vaccines examined, which were homologous to the challenge virus, with prime-boost strategies conferring the best protection against infection.

A recombinant avian paramyxovirus serotype 3 expressing the hemagglutinin protein protects chickens against H5N1 highly pathogenic avian influenza virus challenge

Highly pathogenic avian influenza (HPAI) is a devastating disease of poultry and a serious threat to public health. Vaccination with inactivated virus vaccines has been applied for several years as one of the major policies to control highly pathogenic avian influenza virus (HPAIV) infections in chickens. Viral-vectored HA protein vaccines are a desirable alternative for inactivated vaccines. However, each viral vector possesses its own advantages and disadvantages for the development of a HA-based vaccine against HPAIV. Recombinant Newcastle disease virus (rNDV) strain LaSota expressing HA protein vaccine has shown promising results against HPAIV; however, its replication is restricted only to the respiratory tract. Therefore, we thought to evaluate avian paramyxovirus serotype 3 (APMV-3) strain Netherlands as a safe vaccine vector against HPAIV, which has high efficiency replication in a greater range of host organs. In this study, we generated rAPMV-3 expressing the HA protein of H5N1 HPAIV using reverse genetics and evaluated the induction of neutralizing antibodies and protection by rAPMV3 and rNDV expressing the HA protein against HPAIV challenge in chickens. Our results showed that immunization of chickens with rAPMV-3 or rNDV expressing HA protein provided complete protection against HPAIV challenge. However, immunization of chickens with rAPMV-3 expressing HA protein induced higher level of neutralizing antibodies compared to that of rNDV expressing HA protein. These results suggest that a rAPMV-3 expressing HA protein might be a better vaccine for mass-vaccination of commercial chickens in field conditions.

Protection of White Leghorn chickens by recombinant fowlpox vector vaccine with an updated H5 insert against Mexican H5N2 avian influenza viruses

Despite decades of vaccination, surveillance, and biosecurity measures, H5N2 low pathogenicity avian influenza (LPAI) virus infections continue in Mexico and neighboring countries. One explanation for tenacity of H5N2 LPAI in Mexico is the antigenic divergence of circulating field viruses compared to licensed vaccines due to antigenic drift. Our phylogenetic analysis indicates that the H5N2 LPAI viruses circulating in Mexico and neighboring countries since 1994 have undergone antigenic drift away from vaccine seed strains. Here we evaluated the efficacy of a new recombinant fowlpox virus vector containing an updated H5 insert (rFPV-H5/2016), more relevant to the current strains circulating in Mexico. We tested the vaccine efficacy against a closely related subcluster 4 Mexican H5N2 LPAI (2010 H5/LP) virus and the historic H5N2 HPAI (1995 H5/HP) virus in White Leghorn chickens. The rFPV-H5/2016 vaccine provided hemagglutinin inhibition (HI) titers pre-challenge against viral antigens from both challenge viruses in almost 100% of the immunized birds, with no differences in number of birds seroconverting or HI titers among all tested doses (1.5, 2.0, and 3.1 log₁₀ mean tissue culture infectious doses/bird). The vaccine conferred 100% clinical protection and a significant decrease in oral and cloacal virus shedding from 1995 H5/HP virus challenged birds when compared to the sham controls at all tested doses. Virus shedding titers from vaccinated 2010 H5/LP virus challenged birds significantly decreased compared to sham birds especially at earlier time points. Our results confirm the efficacy of the new rFPV-H5/2016 against antigenic drift of LPAI virus in Mexico and suggest that this vaccine would be a good candidate, likely as a primer in a prime-boost vaccination program.

Biotic concerns in generating molecular diagnosis matrixes for 4 avian viruses with emphasis on Marek's disease virus

The great advance in the field of diagnosis of avian viruses is reflecting the highly sophisticated molecular assays of the human and general virology in providing highly sensitive and fast methods of diagnosis. The present review will discuss the biotic factors and the complexities that became evident with the evolution of the novel molecular diagnostic assays with emphasis on 4 avian viruses, chicken anemia, infectious laryngotracheitis, turkey meningoencephalitis, but mainly on Marek's disease virus. To create a biologically meaningful diagnosis, attention should be dedicated to various biotic factors and not only of the diagnostic assay. Included among the important factors are, (a) the sample examined and the sampling strategy, (b) the outcomes of the pathogen amplification ex vivo, (c) the sampling time and its reflection on the disease diagnosis, (d) the impact of simultaneous multiple virus-infections regarding the ability to demonstrate all pathogens and inter- and intra-interactions between the pathogens. A concerted consideration of the relevant factors and the use of advanced molecular diagnostic assay would yield biologically significant diagnosis in real-time that would beneficiate the poultry industry.

Innovative Mucosal Vaccine Formulations Against Influenza A Virus Infections

Despite efforts made to develop efficient preventive strategies, infections with influenza A viruses (IAV) continue to cause serious clinical and economic problems. Current licensed human vaccines are mainly inactivated whole virus particles or split-virion administered via the parenteral route. These vaccines provide incomplete protection against IAV in high-risk groups and are poorly/not effective against the constant antigenic drift/shift occurring in circulating strains. Advances in mucosal vaccinology and in the understanding of the protective anti-influenza immune mechanisms suggest that intranasal immunization is a promising strategy to fight against IAV. To date, human mucosal anti-influenza vaccines consist of live attenuated strains administered intranasally, which elicit higher local humoral and cellular immune responses than conventional parenteral vaccines. However, because of inconsistent protective efficacy and safety concerns regarding the use of live viral strains, new vaccine candidates are urgently needed. To prime and induce potent and long-lived protective immune responses, mucosal vaccine formulations need to ensure the immunoavailability and the immunostimulating capacity of the vaccine antigen(s) at the mucosal surfaces, while being minimally reactogenic/toxic. The purpose of this review is to compile innovative delivery/adjuvant systems tested for intranasal administration of inactivated influenza vaccines, including micro/nanosized particulate carriers such as lipid-based particles, virus-like particles and polymers associated or not with immunopotentiatory molecules including microorganism-derived toxins, Toll-like receptor ligands and cytokines. The capacity of these vaccines to trigger specific mucosal and systemic humoral and cellular responses against IAV and their (cross)-protective potential are considered.

Innovation in Newcastle Disease Virus Vectored Avian Influenza Vaccines

Highly pathogenic avian influenza (HPAI) and Newcastle disease are economically important avian diseases worldwide. Effective vaccination is critical to control these diseases in poultry. Live attenuated Newcastle disease virus (NDV) vectored vaccines have been developed for bivalent vaccination against HPAI viruses and NDV. These vaccines have been generated by inserting the hemagglutinin (HA) gene of avian influenza virus into NDV genomes. In laboratory settings, several experimental NDV-vectored vaccines have protected specific pathogen-free chickens from mortality, clinical signs, and virus shedding against H5 and H7 HPAI viruses and NDV challenges. NDV-vectored H5 vaccines have been licensed for poultry vaccination in China and Mexico. Recently, an antigenically chimeric NDV vector has been generated to overcome pre-existing immunity to NDV in poultry and to provide early protection of poultry in the field. Prime immunization of one-day-old poults with a chimeric NDV vector followed by boosting with a conventional NDV vector has shown to protect broiler chickens against H5 HPAI viruses and a highly virulent NDV. This novel vaccination approach can provide efficient control of HPAI viruses in the field and facilitate poultry vaccination.

Efficacy of a Recombinant Turkey Herpesvirus AI (H5) Vaccine in Preventing Transmission of Heterologous Highly Pathogenic H5N8 Clade 2.3.4.4b Challenge Virus in Commercial Broilers and Layer Pullets

Outbreaks caused by the highly pathogenic avian influenza virus (HPAIV) H5N8 subtype clade 2.3.4.4 were first reported in 2014 in South Korea then spread very rapidly in Asia, to Europe, and for the first time, to North America. Efficacy of a recombinant HVT-AI (H5) vaccine (rHVT-H5) to provide clinical protection as well as to significantly reduce the shedding of an H5N8 challenge virus has already been demonstrated in SPF chickens. The aim of our studies was to test the efficacy of the same rHVT-H5 vaccine in controlling the transmission of a recent Hungarian HPAIV H5N8 challenge virus in commercial chickens. Broilers and layers were vaccinated at day old according to the manufacturer's recommendation and then challenged with a 2017 Hungarian HPAIV H5N8 (2.3.4.4b) isolate at 5 or 7 weeks of age, respectively. Evaluation of clinical protection, reduction of challenge virus shedding, and transmission to vaccinated contact birds was done on the basis of clinical signs/mortality, detection, and quantitation of challenge virus in oronasal and cloacal swabs (regularly between 1 and 14 days postchallenge). Measurement of seroconversion to AIV nucleoprotein was used as an indicator of infection and replication of challenge virus. Our results demonstrated that rHVT-H5 vaccination could prevent the development of clinical disease and suppress shedding very efficiently, resulting in the lack of challenge virus transmission to vaccinated contact chickens, regardless the type of birds. Single immunization with the tested rHVT-H5 vaccine proved to be effective to stop HPAIV H5N8 (2.3.4.4b) transmission within vaccinated poultry population under experimental conditions.

Co-expression of the Hemagglutinin and Neuraminidase by Heterologous Newcastle Disease Virus Vectors Protected Chickens against H5 Clade 2.3.4.4 HPAI Viruses

Avian influenza remains an important zoonotic disease with a significant global impact. The spread of H5 highly pathogenic avian influenza (HPAI) viruses (clade 2.3.4.4) by migratory birds has caused outbreaks in wide geographic regions (Asia, Europe, and North America) with great economic losses during 2014-2015. Efficient vaccines and vaccination approaches are needed to enhance protective immunity against HPAI viruses. Although several vaccination strategies have been developed, none has been satisfactory. Our strategy has been to use avirulent vaccine strain of Newcastle disease virus (NDV) as a vaccine vector for HPAI viruses. For poultry vaccination, we previously generated a new platform of chimeric NDV vector to overcome preexisting maternal antibodies to NDV in poultry. In this study, we have generated vaccine candidates targeting H5 clade 2.3.4.4 HPAI viruses by using our chimeric NDV and conventional NDV strain LaSota vectors for a heterologous prime-boost immunization approach. Co-expression of the HA and NA proteins by our vaccine vectors induced enhanced HPAI virus specific immune responses in specific-pathogen free and broiler chickens prior to challenge. Further, these vaccine candidates efficiently protected broiler chickens from mortality, clinical signs, and shedding of homologous and heterologous H5 HPAI viruses and highly virulent NDV, thus providing a dual vaccination approach in the field.

Characterization of immunogenicity of avian influenza antigens encapsulated in PLGA nanoparticles following mucosal and subcutaneous delivery in chickens

Mucosal vaccine delivery systems have paramount importance for the induction of mucosal antibody responses. Two studies were conducted to evaluate immunogenicity of inactivated AIV antigens encapsulated in poly(D,L-lactide-co-glycolide) (PLGA) nanoparticles (NPs). In the first study, seven groups of specific pathogen free (SPF) layer-type chickens were immunized subcutaneously at 7-days of age with different vaccine formulations followed by booster vaccinations two weeks later. Immune responses were profiled by measuring antibody (Ab) responses in sera and lachrymal secretions of vaccinated chickens. The results indicated that inactivated AIV and CpG ODN co-encapsulated in PLGA NPs (2x NanoAI+CpG) produced higher amounts of hemagglutination inhibiting antibodies compared to a group vaccinated with non-adjuvanted AIV encapsulated in PLGA NPs (NanoAI). The tested adjuvanted NPs-based vaccine (2x NanoAI+CpG) resulted in higher IgG responses in the sera and lachrymal secretions at weeks 3, 4 and 5 post-vaccination when immunized subcutaneously. The incorporation of CpG ODN led to an increase in Ab-mediated responses and was found useful to be included both in the prime and booster vaccinations. In the second study, the ability of chitosan and mannan coated PLGA NPs that encapsulated AIV and CpG ODN was evaluated for inducing antibody responses when delivered via nasal and ocular routes in one-week-old SPF layer-type chickens. These PLGA NPs-based and surface modified formulations induced robust AIV-specific antibody responses in sera and lachrymal secretions. Chitosan coated PLGA NPs resulted in the production of large quantities of lachrymal IgA and IgG compared to mannan coated NPs, which also induced detectable amounts of IgA in addition to the induction of IgG in lachrymal secretions. In both mucosal and subcutaneous vaccination approaches, although NPs delivery enhanced Ab-mediated immunity, one booster vaccination was required to generate significant amount of Abs. These results highlight the potential of NPs-based AIV antigens for promoting the induction of both systemic and mucosal immune responses against respiratory pathogens.

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.

Avian Vaccination: Current Options and Strategies

Researchers have generated an array of potential avian antiviral vaccines. However, vaccine and viral complexity, small profit margins, the cost of development and manufacturing, and the small population at risk relegate most avian vaccine use to commercial species. Some vaccines designed for use in nonavian species are used to prevent or ameliorate disease in exotic and companion birds. This article highlights newly developed vaccines that may be used in exotic and pet birds. Information pertinent to vaccine choice and strategy is provided, including disease lethality, species affected, and previous knowledge regarding vaccine safety and efficacy. Other avian species of concern are also included.

Efficacy and synergy of live-attenuated and inactivated influenza vaccines in young chickens

Outbreaks of novel highly pathogenic avian influenza viruses have been reported in poultry species in the United States since 2014. These outbreaks have proven the limitations of biosecurity control programs, and new tools are needed to reinforce the current avian influenza control arsenal. Some enzootic countries have implemented inactivated influenza vaccine (IIV) in their control programs, but there are serious concerns that a long-term use of IIV without eradication may result in the selection of novel antigenically divergent strains. A broadly protective vaccine is needed, such as live-attenuated influenza vaccine (LAIV). We showed in our previous studies that pc4-LAIV (a variant that encodes a C-terminally truncated NS1 protein) can provide significant protection against heterologous challenge virus in chickens vaccinated at 2–4 weeks of age through upregulation of innate and adaptive immune responses. The current study was conducted to compare the performances of pc4-LAIV and IIV in young chickens vaccinated at 1 day of age. A single dose of pc4-LAIV was able to induce stronger innate and mucosal IgA responses and protect young immunologically immature chickens better than a single dose of IIV. Most importantly, when 1-day-old chickens were intranasally primed with pc4-LAIV and subcutaneously boosted with IIV three weeks later, they showed a rapid, robust, and highly cross-reactive serum antibody response and a high level of mucosal IgA antibody response. This vaccination regimen warrants further optimization to increase its range of protection.

Challenges of influenza A viruses in humans and animals and current animal vaccines as an effective control measure

Influenza A viruses (IAVs) are genetically diverse and variable pathogens that share various hosts including human, swine, and domestic poultry. Interspecies and intercontinental viral spreads make the ecology of IAV more complex. Beside endemic IAV infections, human has been exposed to pandemic and zoonotic threats from avian and swine influenza viruses. Animal health also has been threatened by high pathogenic avian influenza viruses (in domestic poultry) and reverse zoonosis (in swine). Considering its dynamic interplay between species, prevention and control against IAV should be conducted effectively in both humans and animal sectors. Vaccination is one of the most efficient tools against IAV. Numerous vaccines against animal IAVs have been developed by a variety of vaccine technologies and some of them are currently commercially available. We summarize several challenges in control of IAVs faced by human and animals and discuss IAV vaccines for animal use with those application in susceptible populations.

Coadministration of Recombinant Adenovirus Expressing GM-CSF with Inactivated H5N1 Avian Influenza Vaccine Increased the Immune Responses and Protective Efficacy Against a Wild Bird Source of H5N1 Challenge

Wild birds play a key role in the spread of avian influenza virus (AIV). There is a continual urgent requirement for AIV vaccines to address the ongoing genetic changes of AIV. In the current study, we trialed a novel AIV vaccine against the wild bird source of H5N1 type AIV with recombinant adenovirus expressing granulocyte monocyte colony-stimulating factor (GM-CSF) as an adjuvant. A total of 150-day-old commercial chicks, with AIV-maternal-derived antibody, were divided into 6 groups. The primary vaccination was performed at day 14 followed by a subsequent boosting and intramuscular challenge on day 28 and 42, respectively. Recombinant GM-CSF (rGM-CSF) expressed by adenovirus, named as rAd-GM-CSF, raised the hemagglutination inhibition (HI) titers (log₂) against AIV from 7.0 (vaccinate with inactivated vaccine alone) to 8.4 after booster immunization. Moreover, the rGM-CSF addition markedly increased the expression of interferon-γ, interleukin-4, and major histocompatibility complex-II in the lungs, compared with those immunized with inactivated vaccine alone on day 29, that is, 18 h post booster immunization. Following challenge, chicks inoculated with the inactivated AIV vaccine and rAd-GM-CSF together exhibited mild clinical signs and 62% survivals compared to 33% in the group immunized with inactivated AIV vaccine alone. Higher level of HI titers, immune related molecule expressions, and protection ratio demonstrates a good potential of rGM-CSF in improving humoral and cell mediated immune responses of inactivated AIV vaccines.

Short- and long-term protective efficacy against clade 2.3.4.4 H5N2 highly pathogenic avian influenza virus following prime-boost vaccination in turkeys

Highly pathogenic avian influenza virus (HPAIV) infections are frequently associated with systemic disease and high mortality in domestic poultry, particularly in chickens and turkeys. Clade 2.3.4.4 represents a genetic cluster within the Asian HPAIV H5 Goose/Guangdong lineage that has transmitted through migratory birds and spread throughout the world. In 2014, clade 2.3.4.4 strains entered the U.S. via the Pacific flyway, reassorted with local strains of the North American lineage, and produced novel HPAIV strains of the H5N1, H5N2, and H5N8 subtypes. By 2015, the H5N2 HPAIVs disseminated eastwards within the continental U.S. and Canada and infected commercial poultry, causing the largest animal health outbreak in recent history in the U.S. The outbreak was controlled by traditional mass depopulation methods, but the outbreak was of such magnitude that it led to the consideration of alternative control measures, including vaccination. In this regard, little information is available on the long-term protection of turkeys vaccinated against avian influenza. In this report, a vaccination study was carried out in turkeys using 3 prime-boost approaches with a combination of 2 different vaccines, an alphavirus-based replicon vaccine and an adjuvanted-inactivated reverse genetics vaccine. Vaccine efficacy was assessed at 6 and 16weeks of age following challenge with a prototypic novel clade 2.3.4.4 H5N2 HPAIV. All three vaccines protocols were protective with significantly reduced virus shedding and mortality after challenge at 6weeks of age. In contrast, significant variations were seen in 16-week old turkeys after challenge: priming with the alphavirus-based replicon followed by boost with the adjuvanted-inactivated vaccine conferred the best protection, whereas the alphavirus-based replicon vaccine given twice provided the least protection. Our study highlights the importance of studying not only different vaccine platforms but also vaccination strategies to maximize protection against HPAIV especially with regards to the longevity of vaccine-induced immune response.

Hatchery Vaccination Against Poultry Viral Diseases: Potential Mechanisms and Limitations

Commercial broiler and layer chickens are heavily vaccinated against economically important viral diseases with a view of preventing morbidity, mortality, and production impacts encountered during short production cycles. Hatchery vaccination is performed through in ovo embryo vaccination prehatch or spray and subcutaneous vaccinations performed at the day of hatch before the day-old chickens are being placed in barns with potentially contaminated environments. Commercially, multiple vaccines (e.g., live, live attenuated, and viral vectored vaccines) are available to administer through these routes within a short period (embryo day 18 prehatch to day 1 posthatch). Although the ability to mount immune response, especially the adaptive immune response, is not optimal around the hatch, it is possible that the efficacy of these vaccines depends partly on innate host responses elicited in response to replicating vaccine viruses. This review focuses on the current knowledge of hatchery vaccination in poultry and potential mechanisms of hatchery vaccine-mediated protective responses and limitations.

Newcastle disease virus vectored vaccines as bivalent or antigen delivery vaccines

Recent advances in reverse genetics techniques make it possible to manipulate the genome of RNA viruses such as Newcastle disease virus (NDV). Several NDV vaccine strains have been used as vaccine vectors in poultry, mammals, and humans to express antigens of different pathogens. The safety, immunogenicity, and protective efficacy of these NDV-vectored vaccines have been evaluated in pre-clinical and clinical studies. The vaccines are safe in mammals, humans, and poultry. Bivalent NDV-vectored vaccines against pathogens of economic importance to the poultry industry have been developed. These bivalent vaccines confer solid protective immunity against NDV and other foreign antigens. In most cases, NDV-vectored vaccines induce strong local and systemic immune responses against the target foreign antigen. This review summarizes the development of NDV-vectored vaccines and their potential use as a base for designing other effective vaccines for veterinary and human use.