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For further information, see CMDT Part 33-23: Brucellosis

Key Features

Essentials of Diagnosis

  • History of animal exposure, ingestion of unpasteurized milk or cheese

  • Insidious onset

    • Fatigability

    • Headache

    • Arthralgia

    • Anorexia

    • Sweating

    • Irritability

  • Intermittent fever, especially at night

  • Cervical and axillary lymphadenopathy; hepatosplenomegaly

  • Lymphocytosis, positive blood culture, positive serologic test

General Considerations

  • The infection is transmitted from animals to humans. Brucella abortus (cattle), Brucella suis (hogs), and Brucella melitensis (goats) are the main agents

  • Transmission to humans occurs by

    • Contact with infected meat (slaughterhouse workers)

    • Placentas of infected animals (farmers, veterinarians)

    • Ingestion of infected unpasteurized milk or cheese

  • The incubation period varies from a few days to several weeks

  • May become chronic


  • In the United States, brucellosis is very rare except in the midwestern states (B suis) and in visitors or immigrants from countries where brucellosis is endemic (eg, Mexico, Spain, South American countries)

Clinical Findings

Symptoms and Signs

  • Insidious onset of

    • Weakness

    • Weight loss

    • Low-grade fevers

    • Sweats

    • Exhaustion with minimal activity

  • Headache

  • Abdominal or back pains with anorexia and constipation

  • Arthralgia

  • Hepatosplenomegaly

  • Lymphadenopathy

  • Chronic form

    • May assume an undulant nature, with periods of normal temperature between acute attacks

    • Symptoms may persist for years, either continuously or intermittently

Differential Diagnosis

  • Hodgkin disease

  • Tuberculosis

  • Infective endocarditis

  • Q fever

  • Enteric fever

  • Tularemia

  • Malaria

  • Infectious mononucleosis

  • Influenza

  • HIV infection

  • Disseminated fungal infection, eg, histoplasmosis, coccidioidomycosis


Laboratory Tests

  • The organism can be recovered from cultures of the

    • Blood

    • Cerebrospinal fluid

    • Urine

    • Bone marrow

  • Diagnosis is often made by serologic testing

  • Cultures are more likely to be negative in chronic cases



  • Combination regimens of two or three drugs are more effective

    • Doxycycline, 200 mg/day orally for 6 weeks plus

    • Rifampin, 600 mg/day orally for 6 weeks or

    • Streptomycin, 1 g/day intramuscularly for 2 weeks or

    • Gentamicin, 240 mg intramuscularly once daily for 7 days

  • Longer courses of therapy (eg, several months) may be required to prevent relapse of meningitis, osteomyelitis, or endocarditis



Most frequent

  • Bone and joint lesions such as spondylitis and suppurative arthritis (usually of a single joint)

  • Endocarditis

  • Meningoencephalitis

Less common

  • Pneumonitis with pleural effusion

  • Hepatitis

  • Cholecystitis


Głowacka  P  et al. Brucella—virulence factors, pathogenesis and treatment. Pol J Microbiol. 2018;67:151.
[PubMed: 30015453]  
Pereira  C  et al. Occupational exposure to Brucella spp.: a systematic review and meta-analysis. ...

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