Brucella ovis mutant in ABC transporter protects against Brucella canis infection in mice and it is safe for dogs

Background/Objectives Vaccination is the most important tool for controlling brucellosis, but currently there is no vaccine available for canine brucellosis, which is a zoonotic disease of worldwide distribution caused by Brucella canis. This study aimed to evaluate protection and immune response induced by Brucella ovis Delta abcBA (Bo Delta abcBA) encapsulated with alginate against the challenge with Brucella canis in mice and to assess the safety of this strain for dogs. Methods Intracellular growth of the vaccine strain Bo Delta abcBA was assessed in canine and ovine macrophages. Protection induced by Bo Delta abcBA against virulent Brucella canis was evaluated in the mouse model. Safety of the vaccine strain Bo Delta abcBA was assessed in experimentally inoculated dogs. Results Wild type B. ovis and B. canis had similar internalization and intracellular multiplication profiles in both canine and ovine macrophages. The Bo Delta abcBA strain had an attenuated phenotype in both canine and ovine macrophages. Immunization of BALB/c mice with alginate-encapsulated Bo Delta abcBA (10(8) CFU) induced lymphocyte proliferation, production of IL-10 and IFN-gamma, and protected against experimental challenge with B. canis. Dogs immunized with alginate-encapsulated Bo Delta abcBA (10(9) CFU) seroconverted, and had no hematologic, biochemical or clinical changes. Furthermore, Bo Delta abcBA was not detected by isolation or PCR performed using blood, semen, urine samples or vaginal swabs at any time point over the course of this study. Bo Delta abcBA was isolated from lymph nodes near to the site of inoculation in two dogs at 22 weeks post immunization. Conclusion Encapsulated Bo Delta abcBA protected mice against experimental B. canis infection, and it is safe for dogs. Therefore, B. ovis Delta abcBA has potential as a vaccine candidate for canine brucellosis prevention.