The recombinant feline herpesvirus 1 expressing feline Calicivirus VP1 protein is safe and effective in cats.

Feline herpesvirus type 1 (FHV) and feline calicivirus (FCV) are significant pathogens causing upper respiratory tract disease in cats. Existing inactivated or modified live vaccines against FCV and FHV face limitations in safety and efficacy. To overcome these challenges, a recombinant strain FHV ΔgI/gE-FCV VP1 was developed by deleting the gI/gE gene and concurrently expressing FCV VP1, using the FHV WX19 strain as the parental virus. Results indicated the presence of FCV VP1 in FHV ΔgI/gE-FCV VP1-infected CRFK cells, confirmed through protein blotting and immunofluorescence assays and virus-like particles (VLPs) of FCV were observed using transmission electron microscopy. For efficacy in cats, each animal received intranasal vaccination with 1 mL of FHV ΔgI/gE-FCV VP1 at 10⁶ TCID₅₀. Following completion of vaccination on day 28, animals were exposed to a potent FCV strain. Assessments included clinical signs, nasal shedding, virus neutralizing antibodies, cytokine expression and postmortem histological testing. All vaccinations with FHV ΔgI/gE-FCV VP1 were deemed safe, with significantly reduced clinical disease scores, pathological changes and viral nasal shedding following infection and robust immune responses were induced. These findings collectively suggest the effectiveness of FHV-based recombinant vaccines in preventing FCV infections.