Pathogenesis and pathobiology of brucellosis in livestock.

Brucellaspecies are facultative, intracellular, Gram-negative bacteria with marked tropism for the pregnant reproductive tract of domestic animals. All Brucella species establish persistent infection in the reticuloendothelial system of their natural hosts. The mechanisms of placenta localisation, trophoblast tropism and abortion are poorly understood. A complete picture of the molecular determinants and mechanisms of the cell internalisation process began to emerge only recently. Cyclic beta-1,2-glucan is a molecule secreted into the periplasm of Brucella and is required for intracellular Brucella to avoid fusion of the phagosome with lysosomes. The type IV secretion system translocates Brucella effector proteins into host cells and is critical for both survival and replication of Brucella in infected host cells. Some aspects of the pathogenesis and pathobiology of brucellosis in productive domestic animals are discussed in this section.

Pathological, immunohistochemical and bacteriological study of tissues and milk of cows and fetuses experimentally infected with Brucella abortus.

This report describes a pathological, immunohistochemical and bacteriological study of 42 cows and their progeny (aborted fetuses, weak premature calves, and healthy full-term calves) infected at 6-7 months of gestation by conjunctival inoculation with Brucella abortus. Samples were collected at necropsy within 48 h of abortion or parturition. The most significant lesions were necrotizing and suppurative placentitis and lymphohistiocytic mastitis in cows, and fibrinous pleuritis, fibrinous pericarditis and bronchopneumonia in aborted fetuses. B. abortus was isolated more frequently from milk samples than from mammary tissues, and milk samples from cows with mastitis were often infected. Organisms were often demonstrated immunohistochemically and by culture in tissues showing moderate to severe histological changes.