Brucellosis is a cosmopolitan infectious disease caused by small, facultative intracellular, Gram-negative coccobacilli. Brucella melitensis (goats, sheep, camels, chamois, ibex), B. abortus (cattle, buffalo, bison, zebra, impala, waterbuck, hippopotamus), B. suis (pigs) and B. canis (dogs) are the causative agents of this zoonosis, in descending order of importance. There are several biovars. For example, pigs are infected by B. suis biovars 1, 2 and 3, European wild rabbits by biovar 2. Biovar 4 is found in caribou and reindeer. Humans are accidentally infected and play no role in the survival of these organisms in nature. Animals are the only source of infection and there are no known vectors. B. ovis (sheep) and B. neotomae (desert rats) are not known to cause disease in man. Other species (Brucella pinnipediae, B. maris, B. cetaceae) infect marine mammals, such as seals, dolphins, porpoises, minke whales, etc. There have been rare cases of human infection with some of these marine strains.