Brucellosis
Basics
Description
- Systemic granulomatous bacterial infection caused by Brucella sp. resulting in febrile illness; typically from ingestion of raw milk, unpasteurized milk, infected meat, or contact with secretions from infected animals
- One of the most common worldwide zoonotic diseases
- Incubation period usually 1 to 4 weeks but highly variable and may be several months
- Often presents insidiously with many atypical or nonspecific features
- Characterized by intermittent or irregular fevers and night sweats. Symptoms can range from subclinical disease to infection of almost any organ system.
- Bone and joint involvement is common—20–40% (typically spondylodiscitis).
- Disease may be recurrent, relapsing, or progress to chronic disease.
- System(s) affected: cardiovascular, endocrine/metabolic, gastrointestinal, musculoskeletal, nervous, pulmonary, renal/urologic, skin/exocrine
- Synonym(s): undulant fever; Malta fever; Mediterranean fever; Crimean fever; Bang disease
Pediatric Considerations
- May be mild or subclinical
- Boys infected more than girls (animal handling)
- Children often present with refusal to walk or bear weight.
- Children respond better to antibiotic treatment than do adults.
Alert
High rates of spontaneous abortion (can occur in subclinical cases). Early antibiotic treatment is preventive.
High rates of spontaneous abortion (can occur in subclinical cases). Early antibiotic treatment is preventive.
Epidemiology
- Predominant age: 20 to 45 years (occupational exposure); sometimes children (milk-related outbreaks); can occur at all ages
- Predominant gender:
- Male > female (occupational exposure)
- Female ≥ male (milk exposure)
Incidence
- >500,000 new cases yearly (likely underreported)
- <100 U.S. cases reported annually to the CDC
Prevalence
- Common in developing countries; highest in Turkey, Syria, and Iran; some countries report case rates as high as 10/100,000; present in all inhabited continents
- Highest rates in the United States are among Hispanic populations along U.S.–Mexico border; also Wyoming, North Carolina, Illinois, Florida, and Iowa
- Reportable in all states
Etiology and Pathophysiology
- Brucella ingestion from raw or undercooked tissue or unpasteurized milk products; susceptible to heat and disinfectant but can survive for weeks in frozen food and weeks to months in dust, soil, or water
- Facultative intracellular parasite: gram-negative, nonmotile, non–spore-forming coccobacillus
- Four species pathogenic to humans. Most virulent disease: Brucella melitensis, Brucella suis; also Brucella canis, Brucella abortus; can enter via mucous membrane or broken skin; occasionally inhaled
- Laboratory workers at high risk of infection if specimens handled improperly
- Person-to-person transmission is rare; sexual, vertical, (possibly) breast milk; blood transfusion
- Potential airborne biologic weapon
- Affects most domesticated ungulates (goats, cattle, camels, pigs, sheep), also wild bison and elk. Marine mammals also implicated in zoonotic transmission.
- Infection increases abortion rate in animals, less so in humans.
Genetics
- Some evidence for intrauterine transmission; no reported birth defects
- Some complications may have genetic predisposition.
Risk Factors
- In the United States, occupational exposure to infected animals (cattle and sheep): veterinarians, meat processors, accidental exposure to vaccine, lab technicians, recent immigrants
- Consumer exposure to unpasteurized dairy products and cheese
- Travel to endemic countries (Mediterranean, Middle East, North and East Africa, Central Asia, India, Mexico, Central and South America)
- Chronically ill and malnourished
- Potential acceleration of HIV disease
- Iron deficiency increases susceptibility.
- Bison and elk are infected with brucellosis near Yellowstone Park.
General Prevention
- Avoid infected, unpasteurized dairy products.
- Use caution handling animal vaccines. Use protective goggles and protective gloves when handling tissue.
- Human vaccine under investigation
- Postexposure prophylaxis same as treatment
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Citation
Domino, Frank J., et al., editors. "Brucellosis." 5-Minute Clinical Consult, 33rd ed., Wolters Kluwer, 2025. Medicine Central, im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/1688814/all/Brucellosis.
Brucellosis. In: Domino FJF, Baldor RAR, Golding JJ, et al, eds. 5-Minute Clinical Consult. Wolters Kluwer; 2025. https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/1688814/all/Brucellosis. Accessed October 11, 2024.
Brucellosis. (2025). In Domino, F. J., Baldor, R. A., Golding, J., & Stephens, M. B. (Eds.), 5-Minute Clinical Consult (33rd ed.). Wolters Kluwer. https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/1688814/all/Brucellosis
Brucellosis [Internet]. In: Domino FJF, Baldor RAR, Golding JJ, Stephens MBM, editors. 5-Minute Clinical Consult. Wolters Kluwer; 2025. [cited 2024 October 11]. Available from: https://im.unboundmedicine.com/medicine/view/5-Minute-Clinical-Consult/1688814/all/Brucellosis.
* Article titles in AMA citation format should be in sentence-case
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