Location: Endemic Poultry Viral Diseases Research
2021 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
Turkey coronavirus (TCoV) causes turkey clinical enteric disease, resulting in substantial economic losses to the turkey industry globally. To date, there is no commercial vaccine currently available to prevent the disease. Like most enteric viruses, TCoV does not readily grow in cell cultures, which hampers the conventional vaccine development. To overcome this drawback, ARS researchers in Athens, Georgia, invented a new approach to develop a Newcastle disease virus (NDV) vectored TCoV vaccine. Three NDV LMV vaccine strain-based recombinants expressing a major antigenic protein (S, S1, or N) of TCoV North Carolina 2012 strain were generated using reverse genetics technology. Biological assessments showed that these recombinant viruses retained a similar growth ability in chicken embryos and an avirulent (non-virulent) pathotype in day-old chicks as their parental virus, indicating they were safe as vaccine candidates. However, vaccination of specific-pathogen-free turkeys with 106 EID50/bird of these recombinant viruses did not confer sufficient protection against TCoV challenge. Detection of vaccine virus replication in turkey intestines revealed that these LMV strain-based recombinants replicated poorly, which probably accounted for the failure to induce sufficient immune responses against TCoV challenge. Currently, ARS scientists are searching for an NDV vaccine strain that can efficiently replicate in the turkey intestines as a vector for the TCoV vaccine development.
Codon pair deoptimization (CPD) is a highly efficient virus attenuation strategy that utilizes suboptimal codon pairs to achieve attenuation of recoded viruses. To attenuate Newcastle disease virus (NDV) LaSota (LS) vaccine strain as an in ovo vaccine vector, ARS researchers in Athens, Georgia, manipulated the LS vaccine by CPD of the major surface glycoprotein genes, HN and F, using reverse genetics technology. Biological assays showed that the HN and F+HN gene CPD viruses were slightly attenuated with a lower intracerebral pathogenicity index (ICPI 0.01 and 0.00, respectively) than the LS and the F gene CDP virus (0.15 and 0.36, respectively). Western blot analysis revealed that the HN and F+HN gene CPD viruses decreased the expression of HN protein compared to the LS control. The results suggest that CPD of the HN gene could reduce the HN protein expression, resulting in attenuation of the LS virus.
Accomplishments
1. Turkey coronavirus (TCoV) can cause a highly contagious enteric disease in turkeys with severe economic losses in the global turkey industry. To date, no commercial vaccines are available for control of the disease. Many factors could obstruct the TCoV vaccine development. Undoubtedly, the lack of a TCoV disease model for the evaluation of a vaccine protective efficacy is an important one. To establish a TCoV disease model, ARS researchers in Athens, Georgia, isolated a field strain (NC1743) of TCoV and evaluated its pathogenicity in specific-pathogen-free (SPF) turkey poults. The results showed that this TCoV strain was highly pathogenic and able to reproduce a typical enteric disease in day-old turkey poults with a standard minimal infectious dose. As the age increases, turkey poults became less sensitive to TCoV infection. The overall data suggest that young turkeys infected with the TCoV NC1743 strain could be used as a TCoV disease model to study the disease pathogenesis, and the minimal infectious dose of TCoV NC1743 could be used as a challenge virus to evaluate a vaccine protective efficacy.
Review Publications
Liu, T., Zhang, Y., Cao, Y., Jiang, S., Sun, R., Yin, J., Gao, Z., Ren, G., Wang, Z., Yu, Q., Sui, G., Sun, X., Sun, W., Xiao, W., Li, D. 2020. Optimization of oncolytic effect of Newcastle disease virus Clone30 by selecting sensitive tumor host and constructing more oncolytic viruses. Gene Therapy. https://doi.org/10.1038/s41434-020-0145-9.
He, J., An, Y., Qi, J., Cui, L., Yang, K., Liu, M., Qu, B., Yan, S., Yin, J., Jing, X., Dong, H., Yu, Q., Li, D., Wu, Y. 2020. The recombinant Newcastle disease virus Anhinga strain expressing human TRAIL exhibit antitumor effects on a glioma nude mice model. Journal of Medical Virology. 93(6):3890-3898. https://doi.org/10.1002/jmv.26419.
