Suitability of canine herpesvirus as a vector for oral bait vaccination of foxes

Abstract

Studies were conducted to evaluate the feasibility of using canine herpesvirus (CHV) as a vaccine vector for bait-delivered oral vaccination of wild foxes. To test the viability of CHV in baits, CHV was freeze-dried, incorporated into different baits, stored, and the remaining viral infectivity tested in cell culture after varying periods of time at different storage temperatures. Experimental baits (mouse carcasses) and commercial baits (FOXOFF and PROBAIT) were prepared with either liquid or freeze-dried CHV and tested in two fox trials for their capacity to induce CHV-specific antibodies following oral baiting. Freeze-drying and storage temperatures below 0 degrees C had a stabilizing effect to virus infectivity. When stored at -20 degrees C, freeze-dried CHV retained its full infectivity for up to 3 months in PROBAIT baits, the remaining infectivity in FOXOFF baits was 100-fold less. Oral baiting with CHV induced antiviral serum antibodies in all vaccinated foxes (20/20). None of the vaccinated foxes became ill or shed infectious virus into the environment although viral DNA was detected in body secretions as evaluated by PCR. The results indicate that CHV can be freeze-dried and stored over extended periods of time without loosing much of its infectivity. This is the first report of CHV being used for oral bait vaccination of foxes. It appears that CHV is well suited for use as a recombinant vector for wild canids.

Immunogenicity Studies in Carnivores Using a Rabies Virus Construct with a Site-Directed Deletion in the Phosphoprotein

“…The balance that must be attained is constructing a viral delivery system that is fully attenuated to render it safe and prevent replication and yet have sufficient viral characteristics that allow uptake into permissive cells and protein production to induce an immune response. A further important limitation of some of these recombinant constructs is the interference of preexisting immunity to the vector virus, severely compromising its efficacy [ 26 – 28 ]. Preexisting immunity to the vector virus would not be important for highly attenuated rabies virus constructs.…”

Oral immunocontraceptive vaccines: A novel approach for fertility control in wildlife

“…15,71 Canine herpesviruses are members of the alpha-herpesvirus subfamily, which are readily genetically modified, nontransmissible, relatively species-specific, and can be administered orally. 72,73 But, none of the foxes that received the first intravenous injection and two intranasal boosts produced anti-fZPC IgG antibodies. 74 In conclusion, the ultimate goal of generating an orally delivered immunocontraceptive vaccine by virus and bacteria has not been achieved because no vaccines have induced sustained contraception.…”

“…RRV would offer the best option for an oral immunocontraceptive vaccine because of its good practice characteristics as a non‐disseminating engineered virus and successful application in rabies elimination 15,71 . Canine herpesviruses are members of the alpha‐herpesvirus subfamily, which are readily genetically modified, nontransmissible, relatively species‐specific, and can be administered orally 72,73 . But, none of the foxes that received the first intravenous injection and two intranasal boosts produced anti‐fZPC IgG antibodies 74 …”

“…Finally, environmental factors may have an impact on the stability of peptide antigens or delivery systems, including temperatures, pH, light intensity, humidity, etc. The stability of vaccines should be evaluated in different commercial baits, at different storage temperatures and with several different additives 73 . In addition to the environmental challenges, regulatory and legislative requirement for implementation in wildlife must be addressed.…”

Development and validation of a real-time PCR assay for specific and sensitive detection of canid herpesvirus 1

“…Diagnosis of CHV-1 infection usually relies on virus isolation in canine cell culture. The polymerase chain reaction (PCR) has been established for detection of CHV-1 nucleic acid (Burr et al, 1996;Schulze and Baumgärtner, 1998;Miyoshi et al, 1999;Ronsse et al, 2005;Reubel et al, 2006). A real-time PCR assay has also been developed to monitor virus shedding in the ocular secretions after experimental reactivation of latent CHV-1 (Ledbetter et al, 2009b).…”