Brucellosis, also known as undulant fever, Malta fever, and Bang's disease, is a systemic infection characterized by an undulant (intermittent) fever pattern. While the distribution is worldwide, higher incidence is found in the Mediterranean Basin, South and Central America, Eastern Europe, Asia, Africa, the Caribbean, and the Middle East. Brucellosis is more common in countries without effective animal disease control programs.

Typically a zoonotic infection of farm animals, the disease is produced in humans by infection with the gram-negative coccobacilli of the genus Brucella. Natural infection in humans occurs by skin contact with or ingestion of infected animal tissues or fluids, or through the respiratory tract by inhalation of animal fluid aerosols.

Person-to-person transmission is rare. The species of Brucella that cause infection in humans are Brucella melitensis (sheep, goats, and camels), Brucella suis (pigs), Brucella ovis (sheep and goats), Brucella abortus (cattle), and rarely Brucella canis (dogs). Brucella suis and B melitensis are the most common cause of brucellosis in humans.

Brucellosis produces both an acute and a debilitating chronic illness. The incubation period of brucellosis is 5 days to more than 6 months (most commonly 5-60 days). Human infection is usually due to ingestion of contaminated dairy foods (including raw milk) or infected animals (eg, sheep, cattle, or goats) or through skin wounds.

Typical acute systemic symptoms are nonspecific and flu-like and include undulant fevers, chills, sweats, malaise, myalgias, arthralgias, back pain, fatigue, anorexia, headache, and irritability. Gastrointestinal symptoms are common and include nausea, vomiting, diarrhea, ileitis, colitis, and hepatitis. Other findings include bone pain due to focal infection, pleuritic chest pain, and cough. Adenopathy, pharyngitis, and rash occur more commonly in children. Infection may progress to include the liver, bone marrow, spleen, central nervous system (meningitis), or heart (endocarditis). In pregnant patients, Brucella infections can be associated with miscarriage.

Osteoarticular infections of the spine with paravertebral abscesses are common. Medium and large joints are also commonly infected. Genitourinary involvement can lead to pyelonephritis, cystitis, and epididymoorchitis. Infection with Brucella can lead to chronic painful symptoms lasting months. Mortality rates are less than 2% and are often associated with endocarditis.

Those at greatest risk are slaughterhouse workers, meat inspectors, hunters, veterinarians, tourists, laboratory workers, and those who ingest unpasteurized dairy products.

Aerosolized Brucella is highly infectious. Bioterrorism may be suspected in widespread outbreaks, as Brucella is known to have been weaponized by several countries.