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

Key Features

Essentials of Diagnosis

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

  • Insidious onset

    • Fatigability

    • Headache

    • Arthralgia

    • Anorexia

    • Sweating

    • Irritability

  • Intermittent fever, especially at night, which may become chronic and undulant

  • Cervical and axillary lymphadenopathy; hepatosplenomegaly

  • Lymphocytosis, positive blood culture, elevated agglutination titer

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

  • The disorder 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

  • Epididymitis occurs in 10% of cases in men

  • 50% of cases have peripheral lymph node enlargement and splenomegaly; hepatomegaly is less common

  • 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

  • Lymphoma

  • Tuberculosis

  • Infective endocarditis

  • Q fever

  • Typhoid fever

  • Tularemia

  • Malaria

  • Infectious mononucleosis

  • Influenza

  • HIV infection

  • Disseminated fungal infection, eg, histoplasmosis, coccidioidomycosis


  • Early in the course of infection, the organism can be recovered from the blood, cerebrospinal fluid, urine, and bone marrow

  • Most modern culture systems can detect growth of the organism in blood by 7 days; cultures are more likely to be negative in chronic cases

  • Diagnosis is often made by serologic testing

    • Rising serologic titers or an absolute agglutination titer of > 1:100 supports the diagnosis


  • Combination regimens of two or three drugs are more effective

  • Either doxycycline plus rifampin or streptomycin (or both) or doxycycline plus gentamicin or trimethoprim-sulfamethoxazole plus rifampin or streptomycin (or both) is effective in doses as follows

    • Doxycycline, 100 mg twice daily orally for 6 weeks

    • Trimethoprim, 320 mg/day, plus sulfamethoxazole, 1600 mg, three times weekly orally for 6 weeks

    • Rifampin, 600–1200 mg once daily orally for 6 weeks

    • Streptomycin, 500 mg twice daily intramuscularly for 2 weeks

    • Gentamicin 5 mg/kg/day in three divided doses intravenously for 5–7 days

  • Longer courses of therapy (eg, several months) may be required to cure relapses, osteomyelitis, or meningitis


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