Location: Animal Disease Research
2022 Annual Report
Objectives
Malignant catarrhal fever (MCF) is an often-fatal viral disease that affects primarily ruminants. The disease is caused by gamma herpesviruses in the MCF group of the Macavirus genus. These viruses are carried asymptomatically by certain animal species that serves as virus reservoirs but can cause disease when transmitted to other non-adapted, susceptible species. Ovine herpesvirus-2 (OvHV-2), transmitted by sheep, is globally distributed and the most frequent cause of MCF worldwide. In North America, sheep-associated MCF is a leading cause of death in American bison, which are highly susceptible to the disease. Overall, MCF results in significant economic impact to agriculture not only due to the loss of animals but also because it imposes restrictions to multispecies operations. With no treatment or vaccines available, currently the only way to control the disease is separating carrier and susceptible animals. Therefore, availability of an effective vaccine to MCF and reliable diagnostic assays are top priorities for the agricultural industry. Using rabbits as a laboratory animal model, we have recently demonstrated that protection to MCF can be achieved when using recombinant viral vectors carrying OvHV-2 genes as potential vaccines. In this project we propose to test the safety, efficacy, and duration of protection of selected vaccine candidates in relevant livestock species. We also plan to improve disease control by developing a point-of-care serological assay for detection of MCF virus reservoirs.
Objective 1: Assess the safety and efficacy of new MCF vaccine platforms and delivery systems.
Sub-objective 1.A: Evaluate the safety of immunogen formulations to deliver OvHV-2 gB as an SA-MCF vaccine in cattle and bison.
Sub-objective 1.B: Determine the efficacy of a vaccine targeting OvHV-2 gB in preventing SA-MCF in bison.
Sub-objective 1.C: Assess the risk of SA-MCF vaccinated bison to develop MCF upon exposure to OvHV-2 infected sheep.
Objective 2: Improve MCF diagnosis by developing new optimized diagnostic assays.
Approach
This project focuses on two important aspects of malignant catarrhal fever (MCF) research: Objective 1 is development of a safe and effective sheep-associated (SA)-MCF vaccine for clinically susceptible species and Objective 2 is improvement of diagnostic capabilities for detection of MCF virus reservoirs. In Sub-objective 1.A, we will test a recombinant viral vectored vaccine expressing ovine herpesvirus-2 (OvHV-2) glycoprotein B (gB) in cattle and bison to determine its safety and immunogenicity. Vaccination will be done with the viral vector in adjuvant alone or following prime immunization with DNA encoding OvHV-2 gB. Experimental animals will be monitored for potential adverse effects from immunizations and development of immune responses to the OvHV-2 antigen. Our hypothesis is that immunization with the vaccine formulations and regimes tested does not cause adverse reactions in cattle or bison. In Sub-objective 1.B, we will determine the efficacy of a vaccine in preventing SA-MCF in bison. The hypothesis for this sub-objective is that immunization with a vaccine targeting OvHV-2 gB protects bison from SA-MCF following challenge with a lethal dose of OvHV-2. Experimental animals will be challenged at different times post-vaccination to evaluate the duration of protection induced by vaccination. In Sub-objective 1.C, we will assess the risk of SA-MCF vaccinated bison to develop MCF upon exposure to OvHV-2 infected sheep. This will be a field trial to test the hypothesis that bison immunized with the SA-MCF vaccine have reduced risk of developing MCF than non-vaccinated animals when exposed to OvHV-2 infected sheep. Vaccinated and non-vaccinated control bison will be exposed to a flock of OvHV-2 infected sheep maintained at close proximity for at least 3 months. Development of disease in both groups will be used to calculate protection rates and risks. In Objective 2 we will improve MCF diagnosis by developing a point-of-care serological assay for detection of MCFV antibodies. The goal is to validate and optimize a lateral flow immunoassay using recombinant OvHV-2 gB coupled to quantum dots as antigen. This is expected to result in a rapid, simple, sensitive, and inexpensive method to identify infected animals that can serve as viral reservoirs.
Progress Report
In support of Objective 1, research was performed to 1) evaluate routes for delivery of a viral-vectored vaccine for sheep-associated malignant catarrhal fever (SA-MCF); 2) generate a new recombinant virus as vaccine candidate; and 3) optimize a neutralization assay for assessment of immune responses induced by vaccination. Briefly, an experiment was performed in the rabbit model to evaluate routes for administration of a recombinant virus (rAlHV-1/OvHV-2-gB) as a vaccine. The results of this experiment support the use of intramuscular delivery for trials of this vaccine candidate in cattle and bison. We have also prepared another recombinant virus based on BoHV-4 to deliver OvHV-2 glycoprotein B. For this construction, BoHV-4 gB was replaced by the homologous gene from OvHV-2. The virus viability and correct expression of the heterologous gB were confirmed in vitro. The recombinant virus was tested in vaccine-challenge trials in rabbits and low protection rates (28.5%) were obtained. Based on these results, this candidate will not be further evaluated as a SA-MCF vaccine. Regarding the assessment of viral neutralizing responses in animals immunized with a recombinant AlHV-1 vectored vaccine, a neutralization assay based on BoHV-4 was optimized. The assay is suitable to be used in vaccine trials in cattle and bison.
In support of Objective 2, new plasmid constructions for expression of OvHV-2 glycoprotein B (gB) in both mammalian and baculovirus systems were obtained. The new plasmids and expression systems are currently being tested and optimized for preparation of an antigen to be used in the lateral flow assay.
Substantial progress was also obtained in subordinate projects that add knowledge and complements the house project. In collaboration with researchers in Norway, field studies in Norway, Iceland, and Finland were performed to estimate the seroprevalence of several pathogens of interest in reindeer, including MCF viruses. These studies showed significant prevalence of MCF virus infected reindeer in Norway and Finland but a low prevalence in Iceland. The information is relevant to better understand the risk of different pathogens for reindeer populations in these countries and guide management strategies to prevent animal losses.
In another subordinate project in collaboration with researchers at Parana, Brazil, the presence of MCF viruses associated with lesions in lungs of cattle diagnosed with bovine respiratory disease (BRD) in Brazil was investigated. Many animals (64/120) were positive for MCF viruses. Although additional studies are necessary, the finding of MCF viruses as a single infection in cattle with pneumonia, suggests that MCF should be considered as primary agents in the development of BRD.
Accomplishments
Review Publications
Tryland, M., Sánchez Romano, J., Nymo, I.H., Breines, E.M., Ancin Murguzur, F.J., Kjenstad, O.C., Li, H., Cunha, C.W. 2021. A screening for virus infections in eight herds of semi-domesticated Eurasian tundra reindeer (Rangifer tarandus tarandus) in Norway, 2013–2018. Frontiers in Veterinary Science. 8. Article 707787. https://doi.org/10.3389/fvets.2021.707787.
Oliveira, T.E., Scuisato, G.S., Pelaquim, I.F., Cunha, C.W., Cunha, L.S., Flores, E.F., Pretto-Giordano, L.G., Lisboa, J.A., Alfieri, A.A., Saut, J.P., Cunha, P.H., Headley, S.A. 2021. The participation of a malignant catarrhal fever virus and Mycoplasma bovis in the development of single and mixed infections in beef and dairy cattle with bovine respiratory disease. Frontiers in Veterinary Science. 8. Article 691448. https://doi.org/10.3389/fvets.2021.691448.
Headley, S.A., Dall Agnol, A.M., Navolar, F.M., Frucchi, A.P., de Matos, A.M., Pereira, P.F., Xavier, A.A., Santos, V.H., Silva, L.E., Depes, V.C., Alfieri, A.F., Cunha, C.W., Alfieri, A.A. 2021. Ovine gammaherpesvirus-2 infection associated with chronic interstitial pneumonia in a sheep. Microbial Pathogenesis. 161. Article 105220. https://doi.org/10.1016/j.micpath.2021.105220.
