Brucellosis, also called undulant fever, or Malta fever, in humans is a highly contagious zoonosis (infectious disease transmitted from animals to humans) caused by bacteria of the genus Brucella. Brucella spp. are small, gram-negative, non-motile, non-spore-forming rods. Brucella spp. are facultative intracellular parasites causing chronic disease, which usually persists for life. Brucellosis is a bacterial disease of both humans and animals recognized since the 19th century.

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