Pathophysiology
Clinical meaning
Brucellosis is a zoonotic infection caused by gram-negative, facultative intracellular coccobacilli of the genus Brucella, transmitted to humans primarily through ingestion of unpasteurized dairy products, direct contact with infected animals or their tissues, or inhalation of aerosolized bacteria. It is one of the most common zoonotic infections worldwide, with an estimated 500,000 new cases annually, predominantly in the Mediterranean basin, Middle East, Central Asia, Latin America, and parts of Africa. The four species that commonly infect humans are Brucella melitensis (from goats and sheep -- most virulent and most common cause worldwide), Brucella abortus (from cattle), Brucella suis (from swine -- can be particularly aggressive), and Brucella canis (from dogs -- least common in humans). The pathogenesis of brucellosis begins with entry of Brucella organisms through mucosal surfaces (GI tract, respiratory tract, conjunctivae) or breaks in the skin. Brucella organisms are small (0.5-0.7 x 0.6-1.5 micrometers), facilitating penetration through mucosal surfaces. Once past the mucosal barrier, Brucella is phagocytosed by macrophages and dendritic cells, but rather than being destroyed within the phagolysosome (the normal fate of most ingested bacteria), Brucella...