Brucellosis is not a sustainable disease in humans. The source of human
infection always resides in domestic or wild animal reservoirs. The routes of
infection are multiple: food-borne, occupational or recreational, linked to travel and even to bioterrorism. New Brucella strains or species may emerge and existing Brucella species adapt to changing social, cultural, travel and agricultural environment. Brucella melitensis is the most important zoonotic agent, followed by Brucella abortus and Brucella suis. This correlates with the fact that worldwide, the control of
bovine brucellosis (due to B. abortus) has been achieved to a greater extent than the control of sheep and goat
brucellosis (due to B. melitensis), these latter species being the most important domestic animals in many developing countries. The long duration and high cost of treatment of human
brucellosis reduces the efficacy of the
therapy. There is no human
vaccine for
brucellosis and the occurrence of
brucellosis is directly linked to the status of animal
brucellosis in a region. In this context, the Word Health Organization has defined the development of a human
vaccine, besides the implementation of control and eradication programs in animals, as a high priority. The pathogenicity for humans of B. suis biovars 1, 3 and 4 is well established, whereas B. suis biovar 2 seems to be less pathogenic. Indeed, although hunters and pig farmers have repeatably experienced infectious contact with B. suis biovar 2 (found in wild boar and outdoor-rearing pigs in Europe), isolation of B. suis biovar 2 from human samples have only been seldom reported. Marine mammal
brucellosis, due to two new proposed Brucella species i.e. B. cetaceae and B. pinnipediae, represents a new zoonotic threat but the pathogenicity for humans of the different Brucella species found in cetaceans and pinnipeds still has to be clearly established.