Pathogenesis of mammary gland infection in the goat (Capra hircus) inoculated with Brucella abortus

Abstract

Ferlpartum goats were Inoculated Intravenously with Brucella abortus » and tissues from mammary glands and supramammary lymph nodes were examined by light and electron microscopy. Brucella abortus was identified in tissues with immunoperoxidase staining and antibody-coated colloidal gold. Brucellae were first seen in macro­ phages and neutrophils throughout the mammary gland parenchyma, but most often in alveolar lumens. In subsequent samples, infected phago­ cytic leukocytes progressively increased in number, especially in duct and alveolar lumens, but also in adjacent epithelium, interstitium, and lymphatics. Brucella abortus was detected in phagosomes and phagolyso­ somes in macrophages and neutrophils. Extracellular brucellae were associated with degenerate and necrotic infected phagocytes. Organisms were infrequently seen in supramammary lymph nodes; when seen, they were in macrophages in subcapsular and cortical sinuses, afferent lymphatics, and throughout the parenchyma. There were no gross lesions in mammary glands. Microscopically, there was a lymphoplasmacytic and histiocytic, lobular and periductal, interstitial mastitis. Supramammary lymph nodes were enlarged, and had lymphofolllcular hyperplasia, medullary plasmacytosls, and sinus histiocytosis. This study suggests that phagocytic leukocytes: (1) transport brucellae into mammary glands; (2) provide a site for intracellular replication in mammary secretions; and (3) transport brucellae from mammary glands to supramammary lymph nodes.