Distribution and Incidence

The three main types of Brucella infection in human populations are widespread around the globe in areas dependent in one way or another on those domestic animals that are the main hosts of the respective organisms. Undulant fever caused by B. melitensis follows the distribution of goats all along the Mediterranean littoral (Malta or Mediterranean fever) as well as in parts of China, India, South Africa, and South America, although pasteurization of milk has substantially reduced its incidence during the second half of the twentieth century. The same applies to B. abortus infections. Contagious abortion of cattle, and with it the disease in humans, has been almost completely eradicated from several countries in northern Europe where the incidence is now very low. The true incidence of B. abortus is difficult to assess because it has low pathogenicity and often causes latent infections.

In the United States, brucellosis is still not uncommon, the causative organism being, in order of importance, B. abortus, B. suis, and lastly B. melitensis. Most cases occur sporadically, although occasional minor outbreaks have been reported. Also, the situation is constantly changing as a result, in part, to various eradication programs.

Bruce's discovery of the causal agent had no immediate impact on the incidence of Malta fever; only after identification of the mode of transmission was there a dramatic fall in number of cases, first in the British armed services in Malta where supplies of goats' milk to the troops were curtailed by 1906. In an island where goats are the almost exclusive source of milk, control of the disease in the civilian population was a much greater problem. It was achieved, in Malta and elsewhere, only after World War II, when pasteurization became generally accepted.

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