The genus Brucella includes four medically relevant species (see tab.) which cause brucellosis (also called undulant fever or Malta fever), a classic zoonosis that primarily affects domestic animals (cattle, goats, dogs, pigs etc). Brucellae are slight, coccoid, Gram-negative rods with no flagella (see fig. Brucella abortus).Human brucellosis infections result from direct contact with diseased animals (dogs, pigs, camels and ruminants, sheep, goats, cattle, bison) or indirectly by way of contaminated foods, in particular unpasteurized milk and milk products (soft cheese etc.). The bacteria invade the body either through the mucosa of the upper intestinal and respiratory tracts or through lesions in the skin, then enter the subserosa or subcutis. From there they are transported by microphages or macrophages, in which they can survive, to the lymph nodes, where a lymphadenitis develops. The pathogens the disseminate from the affected lymph nodes, at first lymphogenously and the hematogenously, finally reaching the liver, spleen, bone, marrow, and other RES tissues, in the cells of which they can survive and even multiply. The granulomas typical of intracellular bacteria develop. From these inflammatory foci, the brucellae can enter the bloodstream intermittently, each time causing one of the typical febrile episodes, which usually occur in the evening and are accompanied by chills. The incubation period is 2-3 weeks.Brucellosis induces inconstant fever, sweating, weakness, anorexia, headaches, depression and muscular and bodily pain.Brucellosis is a zoonosis that affects animals all over the world. Infections B. melitensis occur most frequently in Mediterranean countries, in Latin America, and in Asia. The melitensis brucelloses seen in Europe are either caused by milk products imported from these countries or occur in travellers. B. abortus infections used to be frequent in central Europe.
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