Etiology
B. suis are gram-negative, facultative intracellular coccobacilli and therefore are capable of growing and reproducing inside of host cells, specifically phagocytic cells. They are also non-spore-forming, non-capsulated, and non-motile. Flagellar genes, however, are present in the B. suis genome, but thought to be cryptic remnants because some were truncated and others were missing crucial components of the flagellar apparatus. Interestingly, in mouse models, studies have shown that the flagellum is essential for a normal infectious cycle, where the inability to assemble a complete flagellum leads to severe attenuation of the bacteria.
Brucella suis are differentiated into five biovars (strains), where bv. 1-3 infect boars and pigs and bv.1 and 3 may cause severe diseases in humans. In contrast, bv. 2 found in wild boars in Europe show mild or no clinical signs and cannot infect healthy humans, but do infect pigs and hares.
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