Brucellosis in humans: why is it so elusive?

Abstract

Brucella spp. are small, slow-growing, Gram-negative coccobacilli that are responsible for brucellosis, the most common zoonotic disease worldwide. Brucellosis is a notifiable disease in most countries. Brucellosis is also considered as an occupational, laboratory and travel-acquired disease. Brucella spp. are transmitted through consumption of raw animal products (food-borne brucellosis) and animal contact. They may be spread through droplets in the air; they are traditionally classified as a class B bioterrorism agent. Brucellosis incidents have been reported in relation to domestic animals. Brucella strains have been isolated from terrestrial and marine mammals. Brucella melitensis, B. suis and B. abortus differ in host range, pathogenicity and virulence. B. canis infections have rarely been reported. Current global trends on the incidence of brucellosis are reviewed. Brucellosis is often overlooked and can mimic other conditions; it may be acute, subacute or chronic in presentation, and may involve various body sites. Recent studies on endocarditis, osteoarticular, haematological, neurological and other involvements are reviewed. Relapses in brucellosis should also be considered. Collaboration between the microbiologist and the clinician is important for diagnosis, since diagnosis of brucellosis is based on laboratory testing by serology and, ultimately by culture, in the context of clinical presentation and history of recent or past exposure. Advanced PCR-based techniques may also be used to diagnose brucellosis. Today a combination of antibiotics are recommended in treatment, whereas further therapeutic approaches are possible. New challenges posed by international travel, animal trade, animal movement, and occupational migration to/from endemic countries may increase incidence of human cases and the risk of re-emergence of brucellosis in previously brucellosis free regions such as Northern and Central Europe. Animals are considered to be lifelong carriers of Brucella spp. providing a large continuous source of human infection. A lower incidence of human brucellosis is likely to result from a decrease in incidence of animal brucellosis. Control and surveillance strategies may depend on the level of healthcare development and the prevalence of reservoir hosts in the affected region.