Efficacy of vaccination strategies against intranasal challenge with Brucella abortus in BALB/c mice

Brucellosis is a zoonotic disease affecting 500,000 people worldwide annually. Inhalation of aerosol containing a pathogen is one of the major routes of disease transmission in humans. Currently there are no licensed human vaccines available. Brucella abortus strain RB51 is a USDA approved live attenuated vaccine against cattle brucellosis. In a mouse model, strain RB51 over-expressing superoxide dismutase (SOD) administered intraperitoneally (IP) has been shown to be more protective than strain RB51 against an IP challenge with B. abortus pathogenic strain 2308. However, there is lack of information on the ability of these vaccine strains to protect against intranasal challenge. With the long-term goal of developing a protective vaccine for animals and people against respiratory challenge of Brucella spp., we tested a number of different vaccination strategies against intranasal infection with strain 2308. We employed strains RB51 and RB51SOD to assess the efficacy of route, dose, and prime-boost strategies against strain 2308 challenge. Despite using multiple protocols to enhance mucosal and systemic protection, neither rough RB51 vaccine strains provided respiratory protection against intranasal pathogenic Brucella infection. However, intranasal (IN) administration of B. abortus vaccine strain 19 induced significant (p ≤ 0.05) pulmonary clearance of strain 2308 upon IN challenge infection compared to saline. Further studies are necessary to address host-pathogen interaction in the lung microenvironment and elucidate immune mechanisms to enhance protection against aerosol infection.