Recent advances on our understanding of the pathogenesis of Brucellosis

Brucellosis is one of the most frequent zoonotic infections in the world.  Bacteria of the genus Brucella can infect a wide range of wild and domestic animals. In small and large ruminants, brucellosis can cause abortion, decreased milk production, infertility and lameness. Infected animals can shed Brucella in their milk, which is a major source of infection for man. In man, brucellosis presents as an influenza like infection which, if not properly diagnosed and treated, can become chronic, localizing in many sites of the body. Brucella is a facultative intracellular pathogen it enters and survives and multiplies within host cells. To do this it uses a range of virulence factors. The major virulence factor is the VirB Type IV secretion system, a molecular syringe which injects ‘effector proteins’ which modulate the biology of the infected cell, turning it into a niche permissive for the bacterium to survive and replicate. Control of human brucellosis depends on controlling its source: animal disease. This requires a ‘One Health’ approach with actors in both animal and human health working together. Control measures depend on the levels of incidence of animal brucellosis; surveillance of disease in both the animal and human populations is essential. In endemic situations, mass vaccination is required; followed by vaccination of selected heards and finally test and slaughter as incidence decreases. Three Brucella species, B. melitensis , B. abortus and B. suis are generally associated with human disease. Over recent years a number of new Brucella strains have been identified, from a wide range of mammalian hosts, including cetaceans, seals, monkeys, foxes, small rodents. More recently, atypical strains have been found in amphibians, reptiles and fish.  At present little is known about the zoonotic potential of these atypical strains, however a small number of human infections have been reported. It is possible that they are more common, but are not identified as brucellosis. Brucellosis is one of the most common laboratories acquired infections.  This is generally because the isolate is not correctly identified, and is manipulated without the correct safety procedures. With the availability of new databases, Brucella , even atypical strains can be rapidly and accurately be identified by MALDI-TOF MS. Access to MALDI-TOF MS may be difficult in rural areas and under developed countries. A recently described solvent inactivation protocol allows samples to be sent safely to a central laboratory for testing. Identification to the species level can be performed by PCR.