Brucella Species

  • Diagnosis
  • Background
  • Lab Tests
  • References
  • Related Content

Indications for Testing

  • High level of suspicion based on occupation, activities, or travel history

Laboratory Testing

  • CDC Brucellosis testing and diagnosis information
  • Initial testing
    • CBC, C-reactive protein (CRP), liver function
    • Serology – primary method of diagnosis
    • Agglutination testing – detects IgG, IgM, IgA antibodies
      • Fourfold rise in titer considered diagnostic
    • IgG and IgM by ELISA – not preferred; less sensitive than agglutination
    • Febrile antibodies (febrile agglutinins) testing – not specific for Brucella
  • Gold standard – culture of tissue, blood, or fluids
    • Variable yield
      • 40-90% in acute cases
      • 5-20% in chronic cases
    • May require several weeks because organism is very slow growing and difficult to culture

Differential Diagnosis

Brucellosis (also called undulant fever, Malta fever, Mediterranean fever) is a major bacterial zoonosis involving many mammals, including domestic cows (Brucella abortus), pigs (B. suis), goats/sheep (B. melitensis), and dogs (B. canis). The disease is also found in wild ruminant mammals such as deer, elk, and moose.


  • Incidence – 1/100,000 in U.S.
    • Most common zoonosis worldwide but relatively rare in North America and western Europe
    • Endemic in the Mediterranean, Middle East, Mongolia, Russia, Mexico, and Latin America
  • Transmission
    • Most common route is from eating or drinking infected, unpasteurized dairy products (eg, soft cheeses)
    • Inhalation (primarily from occupational exposure) and via skin wounds and abrasions
    • Vertical transmission via breast feeding


  • Brucella spp (gram-negative coccobacilli)
  • Facultative intracellular pathogens
  • Human infections are caused most frequently by B. melitensis, B. suis and B. abortus; rare infections are caused by B. canis
    • Sheep and goats are the most common reservoir

Risk Factors

  • Occupational or recreational exposure to animals
    • >70% of reported cases occur in the meat-processing and livestock industries
    • Brucella spp are able to penetrate imperceptible cuts or abrasions in the skin, leading to infections from handling infected animals
    • Among laboratory workers preparing cultures for bacterial agents, Brucella presents a higher risk of infection than other organisms

Clinical Presentation

  • Brucellosis in humans has variable incubation time, insidious or abrupt onset, and no pathognomonic symptoms or signs
  • Flu-like symptoms usually appear 1-3 weeks after exposure; during incubation (2-8 weeks), organism resides in the lymph nodes
    • Constitutional (~75% of cases) – fever, chills, headache, weakness
    • Osteoarticular (~22% of cases) – sacroiliitis, spondylitis, osteomyelitis
    • Gastrointestinal (30% of cases) – hepatomegaly (granulomatous hepatitis), splenomegaly
    • Genitourinary (5% of cases)– orchiepididymitis, glomerulonephritis, renal abscesses
    • Neurologic (6% of cases) – peripheral neuropathy, chorea, meningitis/encephalitis
    • Mucocutaneous – purpura, maculopapular lesions, Stevens-Johnson syndrome
    • Pulmonary – pneumonia, pleural effusions
    • Cardiovascular (2% of cases)– endocarditis; aortic valve most common
  • Untreated, the disease tends to become chronic and persist for years
    • Chronic symptoms may also occur up to 1 year from onset of illness and include recurrent fever, arthritis, and fatigue
  • Rarely fatal but can be severely debilitating
    • Mortality low (<1%) and almost exclusively from cardiac complications


  • Control of disease in domestic livestock
  • Avoidance of unpasteurized dairy products, including soft cheeses (especially goat cheese)

Indications for Laboratory Testing

Tests generally appear in the order most useful for common clinical situations.
Click on number for test-specific information in the ARUP Laboratory Test Directory

CBC with Platelet Count and Automated Differential 0040003
Method: Automated Cell Count/Differential

C-Reactive Protein 0050180
Method: Quantitative Immunoturbidimetry

Hepatic Function Panel 0020416
Method: Quantitative Enzymatic/Quantitative Spectrophotometry

Brucella Culture 0060159
Method: Culture/Identification


Time intensive

Because isolation of organism is difficult, serologic tests are generally used for diagnosis

Brucella Antibody (Total) by Agglutination 0050135
Method: Semi-Quantitative Agglutination


Cross-reactions may occur between Brucella and Francisella tularensis antigens and antisera; parallel tests should be run with these antigens

Additional Tests Available

Sedimentation Rate, Westergren (ESR) 0040325
Method: Visual Identification


Determine if elevated as an indicator of endocarditisa

Organism Identification by 16S rDNA Sequencing 0060720
Method: 16S rDNA Sequencing

Aerobic Organism Identification 0060115
Method: Identification. Methods may include biochemical, mass spectrometry, or sequencing.


Include warning if organism suspected to be dangerous pathogen (eg, Salmonella, Shigella, Neisseria meningitides)

For suspected agents of bioterrorism, notify state department of health and refer isolates to state laboratory for identification

Susceptibilities on agents of bioterrorism are not performed at ARUP

Febrile Antibodies Identification Panel 2010805
Method: Semi-Quantitative Agglutination/Semi-Quantitative Indirect Fluorescent Antibody/Qualitative Immunoblot


Includes Brucella Antibody (Total) by Agglutination; Rickettsia rickettsii Antibody, IgM; Rickettsia rickettsii antibody, IgG; Rickettsia typhi Antibody, IgG by IFA; Rickettsia typhi Antibody, IgM by IFA, and Salmonella typhi and paratyphi Antibodies


American Society for Clinical Pathology. Choosing Wisely - Five Things Physicians and Patients Should Question. An initiative of the ABIM Foundation. [Last revision Feb 2015; Accessed: Jan 2016]

General References

Araj G. Update on laboratory diagnosis of human brucellosis. Int J Antimicrob Agents. 2010; 36 Suppl 1: S12-7. PubMed

Franco M, Mulder M, Gilman R, Smits H. Human brucellosis. Lancet Infect Dis. 2007; 7(12): 775-86. PubMed

Mantur B, Amarnath S, Shinde R. Review of clinical and laboratory features of human brucellosis. Indian J Med Microbiol. 2007; 25(3): 188-202. PubMed

Shen M. Diagnostic and therapeutic challenges of childhood brucellosis in a nonendemic country. Pediatrics. 2008; 121(5): e1178-83. PubMed

Medical Reviewers

Last Update: January 2016