Abstract
An efficacious vaccine for sheep-associated malignant catarrhal fever (SA-MCF) is important for the livestock industry. Research towards SA-MCF vaccine development is hindered by the absence of culture systems to propagate the causative agent, ovine herpesvirus-2 (OvHV-2), which means its genome cannot be experimentally modified to generate an attenuated vaccine strain. Alternative approaches for vaccine development are needed to deliver OvHV-2 antigens. Bovine herpesvirus 4 (BoHV-4) has been evaluated as a vaccine vector for several viral antigens with promising results. In this study, we genetically engineered BoHV-4 to express OvHV-2 glycoprotein B (gB) and evaluated its efficacy as an SA-MCF vaccine using a rabbit model. The construction of a viable recombinant virus (BoHV-4-AΔTK-OvHV-2-gB) and confirmation of OvHV-2 gB expression were performed in vitro. The immunization of rabbits with BoHV-4-AΔTK-OvHV-2-gB elicited strong humoral responses to OvHV-2 gB, including neutralizing antibodies. Following intra-nasal challenge with a lethal dose of OvHV-2, 42.9% of the OvHV-2 gB vaccinated rabbits were protected against SA-MCF, while all rabbits in the mock-vaccinated group succumbed to SA-MCF. Overall, OvHV-2 gB delivered by the recombinant BoHV-4 was immunogenic and partly protective against SA-MCF in rabbits. These are promising results towards an SA-MCF vaccine; however, improvements are needed to increase protection rates.
Highlights
PCR resulted in the amplification of expected band sizes using the junction PCR
The sequencing of amplicons matched with the expected sequences of the inserted cassettes and their location into the Bovine herpesvirus 4 (BoHV-4) TK locus
bacterial artificial chromosome (BAC) recombineering using E. coli SW102 successfully replaced the KGK gene cassette in the pBAC-BoHV-4-A∆TK-KGK with the CMV-OvgB-V5 cassette resulting in construction of pBAC-BoHV-4-A∆TK-ovine herpesvirus-2 (OvHV-2)-glycoprotein B (gB) (Figure 1)
Summary
Ovine herpesvirus 2 (OvHV-2) causes a frequently fatal disease called sheep-associated malignant catarrhal fever (SA-MCF) in several ungulates, such as bison, cattle, pigs, and deer [1,2]. In the absence of effective treatments for the disease, vaccine development comes as an option for the livestock industry. SA-MCF can have significant economic impact, in the growing bison industry in the US and Canada, due to the high susceptibility of bison to the disease [3]. Cattle are more resistant to SA-MCF than bison, the disease remains an intermittent problem for the cattle industry as losses can on occasion be high [4]. One of the major constraints for the development of an SA-MCF vaccine is the inability to propagate OvHV-2 in cell culture. Since the virus cannot be modified or attenuated in vitro, alternative approaches for delivering OvHV-2 antigens for immunization are of utmost importance
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