Location: Animal Disease Research
Project Number: 2090-32000-037-00-D
Project Type: In-House Appropriated
Start Date: Oct 1, 2016
End Date: Sep 30, 2021
Malignant catarrhal fever (MCF) is an often fatal viral disease that primarily affects ruminants. Several gammaherpesviruses in the Macavirus genus can cause MCF. These viruses are carried asymptomatically by certain animal species but can cause disease when transmitted to clinically susceptible species. Ovine herpesvirus 2 (OvHV-2) is globally distributed and the most frequent cause of MCF worldwide. In North America, OvHV-2-induced MCF is the leading cause of death in American bison, which are highly susceptible to the disease. MCF results in significant economic impact on agriculture not only due to the loss of animals but also because it imposes restrictions on multispecies grazing. The development of an effective vaccine to MCF is a top priority for the agricultural industry. However, because OvHV-2 cannot be cultured in vitro, conventional methods cannot be utilized to attenuate or modify viruses to be used as a vaccine. In this project, we propose a novel strategy to develop a vaccine against MCF using recombinant non-pathogenic gammaherpesviruses expressing key OvHV-2 glycoproteins to induce immune responses capable of protecting animals from disease. Importantly, we also plan to develop a modified virus neutralization assay to assess vaccine efficacy. Objective 1: Develop and evaluate neutralizing antibody assays for OvHV-2 using in vitro and rabbit models with the goal of assessing vaccine efficacy and protection from MCF. Subobjective 1A. Develop a recombinant AlHV-1 expressing OvHV-2 glycoproteins for an in vitro neutralization assay. Subobjective 1B. Develop and validate an in vitro neutralization assay for detection of OvHV-2 antibodies. Subobjective 1C. Evaluate interference of OvHV-2 neutralizing antibodies in the respiratory tract with virus infection and development of SA-MCF in rabbits. Objective 2: Develop novel and efficacious MCF vaccines for clinically-susceptible species using novel vaccine vector systems and platforms. Subobjective 2A. Develop a recombinant BoHV-4 expressing OvHV-2 gB and gH/gL. Subobjective 2B. Evaluate delivery platforms for immunization with the rBoHV-4/OvHV-2-gB-gH/gL in a rabbit model. Subobjective 2C. Determine whether immunization with a recombinant BoHV-4 expressing OvHV-2 gB and gH/gL prevents MCF in bison.
This proposed research addresses a fundamental gap regarding control of OvHV-2: the development of an SA-MCF vaccine. The inability to propagate OvHV-2 in vitro has been a roadblock not only to develop a vaccine for SA-MCF, but also to perform in vitro neutralization assays for antibodies that block, for example, viral entry. Our approach is to develop recombinant non-pathogenic gammaherpesviruses expressing key OvHV-2 glycoproteins to be used as a vaccine and as an in vitro tool for analysis of neutralizing antibody responses. Using recombination-mediated genetic engineering techniques, we will generate recombinant AlHV-1 (rAlHV-1) mutants that express OvHV-2 glycoproteins required for virus entry, as chimeric viruses for in vitro neutralization assays. The assays will be critical to evaluate OvHV-2 neutralizing antibody responses in vaccinated animals and also potentially useful for detecting infection with OvHV-2 and closely related MCF viruses. Moreover, we will develop a recombinant bovine herpesvirus 4 (BoHV-4) expressing OvHV-2 antigens that can stimulate neutralizing antibody responses, as a vaccine to protect clinically-susceptible species from SA-MCF. Overall the proposed research will test two hypotheses: 1) a chimeric virus expressing OvHV-2 glycoprotein(s) propagates in vitro and can be blocked by OvHV-2 neutralizing antibodies; 2) immunization with recombinant BoHV-4 expressing OvHV-2 glycoproteins will stimulate neutralizing antibodies in the respiratory tract, which will correlate with reduced initial viral loads in lung and protection against lethal OvHV-2 challenge. These hypotheses will be tested through the following objectives: 1) develop and evaluate neutralizing antibody assays for OvHV-2 using in vitro and rabbit models with the goal of assessing vaccine efficacy and protection from MCF; and 2) develop novel and efficacious MCF vaccines for clinically-susceptible species using novel vaccine vector systems and platforms.