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Brucellosis, a bacterial zoonotic disease that affects humans, domesticated livestock and wildlife, is considered one of the most common and economically important zoonoses globally. Brucellosis infection in humans, also known as undulant fever, Mediterranean fever or Malta fever, is a debilitating disease that occurs from exposure to infected animals or contaminated animal products such as unpasteurized milk or dairy products. The disease is misdiagnosed often due to the resemblance with other acute febrile illnesses.

Analysis of cheese and skeletal remains from the town of Herculaneum during the Roman Empire suggest this bacterium has been affecting humans for millennia.1 However, it was not until the nineteenth century during the British occupation of the island of Malta that Sir Arthur Bruce first identified what is now known as Brucella melitensis. There were many theories as to how the disease caused by Microccocus melitensis, the name given to the bacteria by Sir Arthur Bruce, was acquired by humans. It was not until the early 1900s that by serendipity the organism was discovered in Maltese goats’ blood and milk with contaminated milk identified as the source of human infection.2 These findings led to public health campaigns banning goat milk consumption by military authorities thereby eradicating the disease from the military base. During the same period, Bernhard Bang isolated what he referred to as Bacillus abortus, from the uterus of an infected cow and was able to reproduce the disease by experimentally inoculating naïve animals. However, it was not until 1918 that Alice Evans determined that Micococcus melitensis and B. abortus were closely related.3 Since then, a number of Brucella spp. have been identified from a wide variety of animals.


Brucella spp. are classified as α-Proteobacteria, and their closest relatives are the Ochrobactrum spp. that are known to cause opportunistic infections in humans. Brucella sp. are characterized as small, facultative, nonmotile, nonspore forming Gram-negative intracellular coccobacilli. The original classification of the genus Brucella was based on phenotypic characteristics and species were named according to the animal they were first isolated from. Based on genomic analyses, the genus Brucella is considered a single population that evolved in different hosts with distinct phenotypic characteristics. Currently, there are 12 recognized Brucella spp. with a primary animal host preference and secondary hosts having a lesser role in maintenance and or transmission (Table 149-1). The most commonly known Brucella species to cause infections in humans are B. melitensis, B. abortus, B. suis, and B. canis; but human infections caused by other Brucella spp. have been identified (Table 149-1).


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