FIG 1.

Cycle of Brucella abortus in the bovine host and humans. Brucella organisms infect through the mucosal membranes (1); once inside, local professional phagocytes such as Mϕs, DCs, and PMNs internalize the invading bacterium (2). From here, the bacterium moves to regional lymph nodes (3), and then it spreads to different organs of the reticuloendothelial system, such as the lungs, spleen, liver, and BM (4). In the pregnant animal, Brucella invades the placental trophoblasts, replicating extensively within these cells, causing placentitis (5) and abortion in the last trimester of pregnancy (6). The fetus becomes a source of infection for other animals (7) and humans (8). If the newly infected animal is pregnant, the abortive bacterial cycle continues (9). Humans may become infected by direct contact with secretions of animals with brucellosis or through ingestion of unpasteurized, contaminated dairy products (10).