Development and efficacy evaluation of an inactivated Bordetella bronchiseptica vaccine in cats

Bordetella bronchiseptica is a primary feline respiratory pathogen urgently requiring effective vaccines. This study characterizes a highly pathogenic Chinese isolate to establish a feline infection model and systematically evaluate a novel inactivated vaccine.

Strain E20, selected from clinical isolates, is pathogenic to healthy cats (ID₅₀ = 4.64 × 10⁸ CFU), was formulated into an inactivated vaccine (BbIV-E20) using 0.2% formaldehyde and GEL 02 adjuvant. Ten-week-old kittens received two subcutaneous immunizations 14 days apart. At 21 days post-booster, felines were intranasally challenged with 4 × 10⁹ CFU of strain E20.

BbIV-E20 exhibited an excellent in vivo safety profile. Vaccinated felines achieved 100% seroconversion (IgG titers ≥1:128) by 14 days post-primary immunization. Post-challenge, BbIV-E20 conferred complete (100%) clinical protection. Compared to PBS controls-which developed severe macroscopic and microscopic respiratory lesions-immunized cats remained asymptomatic, displaying drastically reduced bacterial shedding and significantly minimized bacterial burdens across pulmonary, cardiac, hepatic, and peripheral blood tissues.

Derived from a representative Asian isolate, BbIV-E20 is highly safe and provides robust protective immunity against feline B. bronchiseptica infection, establishing a solid foundation for the prevention and control of feline bacterial respiratory diseases.