Recombinant fowlpox virus vector-based vaccine completely protects chickens from H5N1 avian influenza virus

Rational approach to vaccination against highly pathogenic avian influenza in Nigeria: a scientific perspective and global best practice

Since 2006, highly pathogenic avian influenza (HPAI) subtypes H5Nx have adversely affected poultry production in Nigeria. Successive waves of infections in the last two decades have raised concerns about the ability to contain infections by biosecurity alone, and evidence of recurrent outbreaks suggests a need for adoption of additional control measures such as vaccination. Although vaccination can be used to control virus spread and reduce the morbidity and mortality caused by HPAI, no country using vaccination alone as a control measure against HPAI has been able to eliminate or prevent re-infection. To inform policy in Nigeria, we examined the intricacies of HPAI vaccination, government regulations, and scientific data regarding what kind of vaccines can be used based on subtype, whether inactivated or live attenuated should be used, when to deliver vaccine either proactively or reactively, where to apply vaccination either in disease control zones, regionally, or nationally, and how to vaccinate the targeted poultry population for optimum success. A resurgence of HPAI outbreaks in Nigeria since 2018, after the country was declared free of the epidemic following the first outbreak in 2006, has led to enhanced intervention. Controlled vaccination entails monitoring the application of vaccines, the capacity to differentiate vaccinated from infected (DIVA) flocks, and assessing seroconversion or other immune correlates of protection. Concurrent surveillance for circulating avian influenza virus (AIV) and analyzing AIV isolates obtained via surveillance efforts for genetic and/or antigenic mismatch with vaccine strains are also important. Countries with high investment in commercial poultry farms like Nigeria may identify and zone territories where vaccines can be applied. This may include ring vaccination to control HPAI in areas or production systems at risk of infection. Before adoption of vaccination as an additional control measure on commercial poultry farms, two outcomes must be considered. First, vaccination is an admission of endemicity. Secondly, vaccinated flocks may no longer be made accessible to international poultry markets in accordance with WOAH trade regulations. Vaccination must therefore be approached with utmost caution and be guided by science-based evidence throughout the implementation strategy after thorough risk assessment. Influenza vaccine research, development, and controlled application in addition to biosecurity may be a precautionary measure in the evolving HPAI scenario in Nigeria.

Spotlight on avian pathology: fowlpox virus

Fowlpox virus is the type species of an extensive and poorly-defined group of viruses isolated from more than 200 species of birds, together comprising the avipoxvirus genus of the poxvirus family. Long known as a significant poultry pathogen, vaccines developed in the early and middle years of the twentieth century led to its effective eradication as a problem to commercial production in temperate climes in developed western countries (such that vaccination there is now far less common). Transmitted mechanically by biting insects, it remains problematic, causing significant losses to all forms of production (from backyard, through extensive to intensive commercial flocks), in tropical climes where control of biting insects is difficult. In these regions, vaccination (via intradermal or subcutaneous, and increasingly in ovo, routes) remains necessary. Although there is no evidence that more than a single serotype exists, there are poorly-described reports of outbreaks in vaccinated flocks. Whether this is due to inadequate vaccination or penetrance of novel variants remains unclear. Some such outbreaks have been associated with strains carrying endogenous, infectious proviral copies of the retrovirus reticuloendotheliosis virus (REV), which might represent a pathotypic (if not newly emerging) variant in the field. Until more is known about the phylogenetic structure of the avipoxvirus genus (by more widespread genome sequencing of isolates from different species of birds) it remains difficult to ascertain the risk of novel avipoxviruses emerging from wild birds (and/or by recombination/mutation) to infect farmed poultry.

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.

Vaccines against avian influenza in poultry

The review presents the latest data about the types of vaccines against avian influenza that are used in current medical practice or are under development. Inactivated whole virion vaccines, live vector vaccines, as well as experimental vaccines developed using genetic engineering techniques (e.g. subunit vaccines, VLP vaccines, DNA vaccines) were considered. The efficiency of influenza reverse genetic technology for the development of prototype vaccine strains was noted.

Viral vector-based influenza vaccines

Antigenic drift of seasonal influenza viruses and the occasional introduction of influenza viruses of novel subtypes into the human population complicate the timely production of effective vaccines that antigenically match the virus strains that cause epidemic or pandemic outbreaks. The development of game-changing vaccines that induce broadly protective immunity against a wide variety of influenza viruses is an unmet need, in which recombinant viral vectors may provide. Use of viral vectors allows the delivery of any influenza virus antigen, or derivative thereof, to the immune system, resulting in the optimal induction of virus-specific B- and T-cell responses against this antigen of choice. This systematic review discusses results obtained with vectored influenza virus vaccines and advantages and disadvantages of the currently available viral vectors.

The evolution of poxvirus vaccines

After Edward Jenner established human vaccination over 200 years ago, attenuated poxviruses became key players to contain the deadliest virus of its own family: Variola virus (VARV), the causative agent of smallpox. Cowpox virus (CPXV) and horsepox virus (HSPV) were extensively used to this end, passaged in cattle and humans until the appearance of vaccinia virus (VACV), which was used in the final campaigns aimed to eradicate the disease, an endeavor that was accomplished by the World Health Organization (WHO) in 1980. Ever since, naturally evolved strains used for vaccination were introduced into research laboratories where VACV and other poxviruses with improved safety profiles were generated. Recombinant DNA technology along with the DNA genome features of this virus family allowed the generation of vaccines against heterologous diseases, and the specific insertion and deletion of poxvirus genes generated an even broader spectrum of modified viruses with new properties that increase their immunogenicity and safety profile as vaccine vectors. In this review, we highlight the evolution of poxvirus vaccines, from first generation to the current status, pointing out how different vaccines have emerged and approaches that are being followed up in the development of more rational vaccines against a wide range of diseases.

Avian influenza vaccines against H5N1 'bird flu'

H5N1 avian influenza viruses (AIVs) have spread widely to more than 60 countries spanning three continents. To control the disease, vaccination of poultry is implemented in many of the affected countries, especially in those where H5N1 viruses have become enzootic in poultry and wild birds. Recently, considerable progress has been made toward the development of novel avian influenza (AI) vaccines, especially recombinant virus vector vaccines and DNA vaccines. Here, we will discuss the recent advances in vaccine development and use against H5N1 AIV in poultry. Understanding the properties of the available, novel vaccines will allow for the establishment of rational vaccination protocols, which in turn will help the effective control and prevention of H5N1 AI.

Vaccination of gallinaceous poultry for H5N1 highly pathogenic avian influenza: current questions and new technology

Vaccination of poultry for avian influenza virus (AIV) is a complex topic as there are numerous technical, logistic and regulatory aspects which must be considered. Historically, control of high pathogenicity (HP) AIV infection in poultry has been accomplished by eradication and stamping out when outbreaks occur locally. Since the H5N1 HPAIV from Asia has spread and become enzootic, vaccination has been used on a long-term basis by some countries to control the virus, other countries have used it temporarily to aid eradication efforts, while others have not used it at all. Currently, H5N1 HPAIV is considered enzootic in China, Egypt, Viet Nam, India, Bangladesh and Indonesia. All but Bangladesh and India have instituted vaccination programs for poultry. Importantly, the specifics of these programs differ to accommodate different situations, resources, and industry structure in each country. The current vaccines most commonly used are inactivated whole virus vaccines, but vectored vaccine use is increasing. Numerous technical improvements to these platforms and novel vaccine platforms for H5N1 vaccines have been reported, but most are not ready to be implemented in the field.

Protection against SHIV-KB9 infection by combining rDNA and rFPV vaccines based on HIV multiepitope and p24 protein in Chinese rhesus macaques

Developing an effective vaccine against HIV infection remains an urgent goal. We used a DNA prime/fowlpox virus boost regimen to immunize Chinese rhesus macaques. The animals were challenged intramuscularly with pathogenic molecularly cloned SHIV-KB9. Immunogenicity and protective efficacy of vaccines were investigated by measuring IFN-γ levels, monitoring HIV-specific binding antibodies, examining viral load, and analyzing CD4/CD8 ratio. Results show that, upon challenge, the vaccine group can induce a strong immune response in the body, represented by increased expression of IFN-γ, slow and steady elevated antibody production, reduced peak value of acute viral load, and increase in the average CD4/CD8 ratio. The current research suggests that rapid reaction speed, appropriate response strength, and long-lasting immune response time may be key protection factors for AIDS vaccine. The present study contributes significantly to AIDS vaccine and preclinical research.

Immune responses of chickens inoculated with a recombinant fowlpox vaccine coexpressing HA of H9N2 avain influenza virus and chicken IL-18

Control of the circulation of H9N2 avian influenza virus (AIV) is a major concern for both animal and public health, and H9N2 AIV poses a major threat to the chicken industry worldwide. Here, we developed a recombinant fowlpox virus (rFPV-HA) expressing the haemagglutinin (HA) gene of the A/CH/JY/1/05 (H9N2) influenza virus and a recombinant fowlpox virus (rFPV-HA/IL18) expressing the HA gene and chicken interleukin-18 (IL-18) gene. Recombinant plasmid pSY-HA/IL18 was constructed by cloning chicken IL-18 expression cassette into recombinant plasmid pSY-HA containing the HA gene. Two rFPVs were generated by transfecting two recombinant plasmids into the chicken embryo fibroblast cells pre-infected with S-FPV-017, and assessed for their immunological efficacy on one-day-old White Leghorn specific-pathogen-free chickens challenged with the A/CH/JY/1/05 (H9N2) strain. There was a significant difference in HI antibody levels (P<0.05) elicited by either rFPV-HA or rFPV-HA/IL18. The level of splenocyte proliferation response in the rFPV-HA/IL18-vaccinated group was significantly higher (P<0.05) than that in the rFPV-HA group. After challenge with 10(6.5)ELD(50) H9N2 AIV 43days after immunization, rFPVs vaccinated groups could prevent virus shedding and replication in multiple organs in response to H9N2 AIV infection, and rFPV-HA/IL18 vaccinated group had better inhibition of viruses than rFPV-HA vaccinated group. Our results show that the protective efficacy of the rFPV-HA vaccine could be enhanced significantly by simultaneous expression of IL-18.

Assessment of route of administration and dose escalation for an adenovirus-based influenza A Virus (H5N1) vaccine in chickens

Highly pathogenic avian influenza (HPAI) virus causes one of the most economically devastating poultry diseases. An HPAI vaccine to prevent the disease in commercial and backyard birds must be effective, safe, and inexpensive. Recently, we demonstrated the efficacy of an adenovirus-based H5N1 HPAI vaccine (Ad5.HA) in chickens. To further evaluate the potential of the Ad5.HA vaccine and its cost-effectiveness, studies to determine the minimal effective dose and optimal route of administration in chickens were performed. A dose as low as 10(7) viral particles (vp) of adenovirus-based H5N1 vaccine per chicken was sufficient to generate a robust humoral immune response, which correlated with the previously reported level of protection. Several routes of administration, including intratracheal, conjunctival, subcutaneous, and in ovo routes, were evaluated for optimal vaccine administration. However, only the subcutaneous route of immunization induced a satisfactory level of influenza virus-specific antibodies. Importantly, these studies established that the vaccine-induced immunity was cross-reactive against an H5N1 strain from a different clade, emphasizing the potential of cross-protection. Our results suggest that the Ad5.HA HPAI vaccine is safe and effective, with the potential of cross-clade protection. The ease of manufacturing and cost-effectiveness make Ad5.HA an excellent avian influenza vaccine candidate with the ability to protect poultry from HPAI virus infection. Considering the limitations of the influenza vaccine technology currently used for poultry applications, any effort aimed at overcoming those limitations is highly significant.

A safety assessment of a fowlpox-vectored Mycoplasma gallisepticum vaccine in chickens

A recombinant fowlpox virus vaccine expressing key protective Mycoplasma gallisepticum antigens could facilitate in the prevention both of fowlpox virus and M. gallisepticum infections. Vectormune FP-MG vaccine, a recombinant fowlpox virus expressing both M. gallisepticum 40k and mgc genes, was assessed for its safety in 8-wk-old specific-pathogen-free White Leghorn chickens. The vaccine virus was serially passaged 5 times by wing-web inoculation. Based on the postinoculation clinical observation, gross pathological examination of air sacs and peritoneum, genetic stability evaluation, virus shedding and tissue distribution detection, horizontal transmission ability determination, and protection against fowlpox virus challenge, the Vectormune FP-MG vaccine possesses a high level of safety.

Contributions of the avian influenza virus HA, NA, and M2 surface proteins to the induction of neutralizing antibodies and protective immunity

Highly pathogenic avian influenza virus (HPAIV) subtype H5N1 causes severe disease and mortality in poultry. Increased transmission of H5N1 HPAIV from birds to humans is a serious threat to public health. We evaluated the individual contributions of each of the three HPAIV surface proteins, namely, the hemagglutinin (HA), the neuraminidase (NA), and the M2 proteins, to the induction of HPAIV-neutralizing serum antibodies and protective immunity in chickens. Using reverse genetics, three recombinant Newcastle disease viruses (rNDVs) were engineered, each expressing the HA, NA, or M2 protein of H5N1 HPAIV. Chickens were immunized with NDVs expressing a single antigen (HA, NA, and M2), two antigens (HA+NA, HA+M2, and NA+M2), or three antigens (HA+NA+M2). Immunization with HA or NA induced high titers of HPAIV-neutralizing serum antibodies, with the response to HA being greater, thus identifying HA and NA as independent neutralization antigens. M2 did not induce a detectable neutralizing serum antibody response, and inclusion of M2 with HA or NA reduced the magnitude of the response. Immunization with HA alone or in combination with NA induced complete protection against HPAIV challenge. Immunization with NA alone or in combination with M2 did not prevent death following challenge, but extended the time period before death. Immunization with M2 alone had no effect on morbidity or mortality. Thus, there was no indication that M2 is immunogenic or protective. Furthermore, inclusion of NA in addition to HA in a vaccine preparation for chickens may not enhance the high level of protection provided by HA.

Evolutionary repercussions of avian culling on host resistance and influenza virulence

BACKGROUND

Keeping pandemic influenza at bay is a global health priority. Of particular concern is the continued spread of the influenza subtype H5N1 in avian populations and the increasing frequency of transmission to humans. To decrease this threat, mass culling is the principal strategy for eradicating influenza in avian populations. Although culling has a crucial short-term epidemiological benefit, evolutionary repercussions on reservoir hosts and on the viral population have not been considered.

METHODS AND FINDINGS

To explore the epidemiological and evolutionary repercussions of mass avian culling, we combine population genetics and epidemiological influenza dynamics in a mathematical model parameterized by clinical, epidemiological, and poultry data. We model the virulence level of influenza and the selection on a dominant allele that confers resistance against influenza [1, 2] in a poultry population. Our findings indicate that culling impedes the evolution of avian host resistance against influenza. On the pathogen side of the coevolutionary race between pathogen and host, culling selects for heightened virulence and transmissibility of influenza.

CONCLUSIONS

Mass culling achieves a short-term benefit at the expense of long-term detriments: a more genetically susceptible host population, ultimately greater mortality, and elevated influenza virulence.