Abstract
Ovine brucellosis caused by Brucella ovis is a major cause of reproductive failure in sheep. This study aimed to evaluate transplacental infection and pathogenicity of B.ovis wild type strain ATCC 25840 (WT B.ovis) and the candidate vaccine strain Brucella ovis ∆abcBA in pregnant mice. A total of 40 BALB/c mice were equally divided into 4 groups: (i) non immunized and uninfected control mice (3/10 mice became pregnant); (ii) non immunized and challenged with WT Brucella ovis (5/10 pregnant); (iii) inoculated only with Brucella ovis ∆abcBA (6/10 pregnant); (iv) immunized with Brucella ovis ∆abcBA and challenged with WT Brucella ovis (5/10 pregnant). Female mice bred, and five days after visualization of the vaginal plug, they were inoculated intraperitoneally (ip) with 100 μL of sterile PBS, 100 μL of 1x106 CFU of Brucella ovis ∆abcBA, or 100 μL of 1x106 CFU of Brucella ovis WT, according to each group. At the 17th day of gestation, samples ofspleen, liver, uterus, placenta, fetus and mammary gland were obtained for bacteriology, histopathology and immunohistochemistry. Non immunized mice challenged with B.ovis WT developed necrotizing placentitis as well as microgranulomas in the liver and spleen. These findings support the notion that B.ovis infection in pregnant mice induces lesions that are similar to those caused by B.abortus in the same animal model. Brucella ovis ∆abcBA was not recovered from any of the sampled organs, and it did not cause any gross or microscopic lesions, indicating that it is a safe and attenuated strain in this experimental model. In addition, Brucella ovis ∆abcBA was induced protective immunity as demonstrated by decreased numbers of B.ovis WT in the liver, uterus and fetuses of immunized mice after the challenge with B.ovis WT.
