Oral Administration Following Subcutaneous Administration of FCV Vaccines Enhances Vaccine Efficacy against Challenge of a Highly Virulent Vs Feline Calicivirus

Feline calicivirus (FCV) is a common cause of upper respiratory and oral disease in cats. Highly virulent systemic strains of FCV (vs FCV) have been described. These vs FCV isolates cause characteristic edema, cutaneous ulcers and other clinical signs typically associated with FCV infection. Vs FCV isolates also cause high mortality even in previously vaccinated cats. We reported previously that the FCV serum cross-neutralization profile of cat serum generated using the oralnasal route of administration is broader than with subcutaneous administration (SC), as measured with a 26-FCV viral panel (Rong et al., Virus Research 122:95-108, 2006). In this report, we tested the in vivo ef- ficacy of the FCV vaccine, in a 4-way (FCV-FHV-FPV-FCp) format, by using a highly virulent vs FCV- 33585 as the challenge virus. Vaccines were administered as 2-dose subcutaneouly (SC/SC), or subcutaneously followed by orally (SC/Oral). The mortality induced by vs FCV-33585 in unvaccinated control cats was 78% (7 out of 9 cats). The mortality decreased to 44% (4 out of 9 cats) with cats vaccinated with the 4-way vaccine given SC/SC. However, when this vaccine was given SC/Oral, the mortality decreased to 10% (1 out of 10 cats). The clinical scores, calculated based on frequency and severity of various clinical signs, correlated with mortality data. These results demonstrated that oral administration of FCV vaccines, as the second dose following the first dose of subcutaneious administration, ehances FCV efficacy against challenge of a highly virulent vs FCV. We propose that not only oral vaccination offers convenience and needle-free inoculation, it also enhances FCV vaccine efficacy.