Location: Endemic Poultry Viral Diseases Research
2020 Annual Report
Objectives
1. Characterize the intestinal virome associated with poultry enteric diseases, including assessing the intestinal microbiome of poultry for the presence of novel enteric pathogens, and developing molecular tools to study the epidemiology, ecology, and evolution of enteric pathogens.
2. Investigate the role of the poultry gut microbiome in promoting overall health and performance gains, including defining the interactions between the gut microbiome and the host immune system that contribute to enteric diseases and performance problems and developing the microbiome as a poultry health phenotype.
3. Develop vaccine platforms that will lead to highly efficacious vaccines that have been rationally designed to control enteric diseases of poultry, including developing vaccines targeting specific enteric pathogens early during the poultry production cycle.
Approach
Viral infections of the avian gastrointestinal tract negatively impact poultry production; however, determining the complex etiologies of the viral enteric diseases in poultry has been difficult. Research in our Unit over the past five+ years has focused in part on the characterization of the poultry gut virus community and initial characterizations of novel viruses. The research proposed in Objective 1 will continue and expand upon this line of investigation. As a logical extension of our viral metagenomic work, we have further performed comparative metagenomic analyses of healthy and enteric disease-affected poultry flocks, leading to descriptions of potential disease-associated viruses such as the enteric picornaviruses. Objective 2 again continues and expands upon these investigations, proposing extensive flock comparisons using powerful next-generation sequencing techniques, pathogenesis work with viruses, and defining the immune response of poultry suffering from enteric maladies. Finally, the discovery of disease-associated genes and infectious agents in Objective 2 will directly inform the design of targeted interventions in Objective 3, which will use our established, efficacious recombinant vectored vaccine platforms to produce vaccines targeting enteric viruses early during the poultry production cycle.
Progress Report
The following research progress reports are related to Objective 3 of this ARS project:
Turkey coronavirus (TCoV) causes turkey clinical enteric disease, resulting in significant economic losses to the turkey industry in the United States and abroad. However, there is no commercial vaccine currently available to prevent the disease. ARS scientists in Athens, Georgia, established a vaccination/challenge model in the natural host, turkeys, to evaluate the TCoV vaccine candidates. One-day-old specific-pathogen-free (SPF) turkeys were infected with the TCoV SEPRL1743 isolate, and after day 4 post-infection, turkeys displayed typical TCoV clinical disease signs. This result demonstrated that the TCoV SEPRL1743 strain is pathogenic and could be used as a challenge virus to evaluate the protective efficacy of the TCoV vaccine candidates in turkeys.
In ovo vaccination (vaccination directly into the incubating egg) is an attractive immunization approach for the poultry industry. Currently available Newcastle disease virus (NDV) vaccines cannot be administered in ovo because of the reduced hatchability and embryo mortality. The codon pair deoptimization (CPD) approach has been used for efficient and rapid attenuation of a variety of RNA viruses. ARS scientists in Athens, Georgia, aimed to attenuate the NDV LaSota (LS) strain for in ovo vaccination by CPD of the fusion (F) or/and hemagglutinin-neuraminidase (HN) genes. Three NDV LS recombinants expressing codon deoptimized LS F (rLS/F-d), HN (rLS/HN-d), or both genes (rLS/F+HN-d) were generated by using reverse genetics technology. Biological assays showed that the codon deoptimized viruses maintained similar biological and pathogenetic properties in embryonated eggs as the parental rLS virus. All three codon deoptimized viruses were still lethal to 10-day-old specific-pathogen-free chicken embryos with a mean death time of fewer than 128 hours. These results suggested that the CPD of the surface glycoprotein genes of the LS strain does not sufficiently attenuate the virus for in ovo vaccination, and other virus attenuation approaches are needed to develop a safe in ovo NDV vaccine.
Accomplishments
1. Many Newcastle disease virus (NDV) strains have been developed as vectors to express a foreign gene (FG) for vaccine and cancer therapy purposes. Since the early 2000s, reverse genetics technology has been used to develop Newcastle disease virus (NDV) vaccine strains as vectors to deliver antigens from other avian pathogens as dual or multivalent vaccines. However, most of these NDV vectors express only a single or two foreign genes (FGs) from suboptimal insertion sites in the NDV genome, obtaining different FG expression or vaccine protection levels. To improve the FG expression, ARS researchers in Athens, Georgia, developed a novel NDV LaSota vaccine-based vector to express two FGs from the identified optimal insertion sites in the NDV genome. Biological assessments showed that the expression of two FGs from the optimal insertion sites was significantly more efficient than those from the suboptimal insertion sites. These results suggest that the NDV LaSota vector could efficiently express two antigens derived from an avian pathogen or two different pathogens as a dual or multivalent vaccine candidate, which will provide a broad protection against poultry infectious diseases.
2. Infectious bronchitis virus (IBV, a coronavirus) causes severe infectious bronchitis (IB) of chickens, resulting in significant economic losses to the poultry industry worldwide. Infectious bronchitis virus (IBV, a coronavirus) causes severe infectious bronchitis (IB) of chickens, resulting in significant economic losses to the poultry industry worldwide. Vaccination with serotype-specific attenuated live IBV vaccines is a common practice to control the disease. However, like most coronaviruses, the IBV vaccine viruses are constantly evolving in the vaccinated chickens. Some of the mutated vaccine subpopulations revert virulence and contribute to the IB outbreaks. Therefore, there is a need to develop a safe, genetically stable, and efficacious vaccine against IB. ARS researchers in Athens, Georgia, in collaboration with scientists at Auburn University, generated a Newcastle disease virus (NDV) LaSota vaccine-based recombinant virus as a vaccine candidate. Biological assessments demonstrated that the new recombinant virus was safe and stable. At 1 or 10 days of age, chickens were vaccinated with different doses of the vaccine and challenged with different virulent IBV Ark strains in two experiments. The results showed that single-dose vaccination provided inefficient protection against the IBV challenge. A higher single-dose or a prime-boost vaccination approach conferred significant clinical protection and reduced tracheal lesions. However, neither single-dose nor a prime-boost vaccination reduced the challenge virus shedding. Thus, further development of the vaccine compositions and vaccination approach is needed to improve the overall vaccine protective efficacy.
Review Publications
Yu, Q., Li, Y., Dimitrov, K., Afonso, C.L., Spatz, S.J., Zsak, L. 2020. Genetic stability of a Newcastle disease virus vectored infectious laryngotracheitis virus vaccine after serial passages in chicken embryos. Vaccine. 38(4):925-932. https://doi.org/10.1016/j.vaccine.2019.10.074.
He, L., Zhang, Z., Yu, Q. 2020. Expression of two foreign genes by a Newcastle disease virus vector from the optimal insertion sites through a combination of the ITU and IRES-dependent expression approaches. Frontiers in Microbiology. 11:769. https://doi.org/10.3389/fmicb.2020.00769.
Zegpi, R.A., He, L., Yu, Q., Joiner, K.S., Van Santen, V.C., Toro, H. 2020. Limited protection conferred by recombinant Newcastle disease virus expressing infectious bronchitis spike protein. Avian Diseases. 64(1):53-59. https://doi.org/10.1637/0005-2086-64.1.53.
