Conditions · Infectious and tropical diseases
Brucellosis !
Brucellosis is a bacterial infection caught from livestock or raw dairy that causes waves of fever and sweats and can settle in the spine and other organs.
Updated 2026-11-01
Structures involved
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Microorganisms that cause it
Why it happens
- Granulomatous inflammation: caseating vs non-caseating, the causes to know
- Fever
- Lymph node and spleen under the microscope
What it is
A zoonotic infection by Brucella species, small gram-negative coccobacilli that live inside macrophages, causing an undulant febrile illness that can become focal (bones and joints, genital tract, heart, nervous system) or chronic.
Who gets it
One of the most common zoonoses worldwide, with highest burden in the Mediterranean, Middle East, Central Asia and parts of Latin America. In Colombia bovine brucellosis (B. abortus) persists in cattle herds and is under a national control programme; human cases are mostly occupational (ranchers, milkers, slaughterhouse workers, veterinarians) or come from raw milk and fresh unpasteurised cheese, and are probably under-diagnosed.
Causes
- Brucella melitensis (goats and sheep; the most virulent), B. abortus (cattle), B. suis (pigs) and B. canis (dogs)
- Ingestion of unpasteurised milk and fresh cheese
- Contact of broken skin or conjunctiva with blood, placentas, aborted fetuses or uterine secretions of infected animals
- Inhalation of aerosols in barns, slaughterhouses or microbiology laboratories
Risk factors
- Work with cattle, goats, sheep or pigs (farmers, milkers, butchers, veterinarians)
- Drinking raw milk or eating fresh unpasteurised cheese
- Assisting animal births or abortions without gloves or eye protection
- Laboratory work with cultures without biosafety precautions (a leading laboratory-acquired infection)
Pathophysiology
Brucella enters through mucosa or skin, is taken up by macrophages and survives inside them by blocking phagosome-lysosome fusion. It travels to regional nodes and then seeds the reticuloendothelial system (liver, spleen, bone marrow, lymph nodes), where it forms non-caseating granulomas. Intermittent release into the blood causes the undulating fever; persistence inside cells explains focal disease, relapses and the need for long combined antibiotic courses.
Classification
- Acute (under 2 months), subacute (2–12 months) and chronic (over 1 year)
- Focal forms: osteoarticular, genitourinary, neurobrucellosis, endocarditis, hepatosplenic
- Relapse: return of symptoms after treatment, usually within months
Symptoms and signs
- Fever, often evening or undulating over weeks, with heavy, sometimes malodorous sweats
- Fatigue, malaise, headache and weight loss
- Back pain and arthralgia; low back pain suggests sacroiliitis or spondylitis
- Hepatomegaly, splenomegaly and lymphadenopathy
- Testicular pain and swelling in men (epididymo-orchitis)
- Depression and poor concentration in chronic forms
Diagnosis
- Clinical
- Suspected in a person with prolonged fever, sweats and arthralgia plus animal or raw dairy exposure. The exposure history is the key clue; the laboratory must be warned because cultures are a biosafety risk.
- Tests
- Blood cultures (slow growth; bone marrow culture has the highest yield). Serology: a rapid agglutination screen (Rose Bengal) confirmed by standard tube agglutination or ELISA; PCR where available. Mild anaemia, leukopenia and raised transaminases are common.
- Imaging
- MRI of the spine for suspected spondylitis (typically lumbar, L4–L5) and sacroiliitis; echocardiography if endocarditis is suspected; abdominal ultrasound for hepatosplenic abscesses.
Differential diagnosis
- Tuberculosis, including spinal tuberculosis (Pott disease)
- Typhoid fever
- Malaria and other prolonged febrile illnesses
- Infective endocarditis from other organisms
- Lymphoma and other causes of fever of unknown origin
Goal of treatment
Clear the intracellular infection with a prolonged combination of antibiotics, treat focal disease, prevent relapse and remove the source of exposure.
Treatment
- Medical
- Combination antibiotic therapy for several weeks: a tetracycline (doxycycline) plus rifampicin or plus an aminoglycoside; monotherapy is avoided because of relapse.
- Medical
- Longer courses and triple regimens for spondylitis, neurobrucellosis and endocarditis; adapted regimens (for example trimethoprim-sulfamethoxazole or rifampicin-based) in pregnancy and young children, in whom tetracyclines are avoided.
- Surgical
- Valve replacement for endocarditis with heart failure or valve destruction; drainage of paravertebral or epidural abscesses causing compression.
- Follow-up
- Follow-up for relapse after treatment; notify the case and investigate the animal or food source; laboratory staff exposed to cultures receive prophylaxis.
Drugs for this condition
Complications
- Spondylitis and sacroiliitis (the most common focal form)
- Peripheral arthritis and osteomyelitis
- Epididymo-orchitis
- Infective endocarditis
- Meningitis, meningoencephalitis and neuropathies
- Miscarriage when acquired in pregnancy
- Chronic and relapsing disease
Prognosis
With correct combination therapy most patients recover; relapse affects about 5–15%, usually within a year. Mortality is low and comes mainly from endocarditis; chronic disease can cause prolonged disability.
Prevention
- Pasteurise milk and dairy; avoid raw milk and fresh unpasteurised cheese
- Gloves, eye protection and covering of skin wounds when handling births, abortions and carcasses
- Vaccination and testing of livestock with removal of infected animals (there is no human vaccine)
- Biosafety-level precautions when processing suspected cultures
Test yourself
Think of the answer, then tap the question to see it.
What exposure history should make you suspect brucellosis in a patient with prolonged fever?
Work with livestock (milking, assisting births, slaughter) or drinking raw milk and eating fresh unpasteurised cheese.
What is the most common focal complication of brucellosis?
Osteoarticular disease, especially sacroiliitis and lumbar spondylitis (often L4–L5).
Why is brucellosis treated with an antibiotic combination for weeks?
Brucella survives inside macrophages, so monotherapy or short courses lead to frequent relapse.
What is the main cause of death in brucellosis?
Infective endocarditis, which may need valve replacement.
Why should the laboratory be warned when brucellosis is suspected?
Brucella cultures are highly infectious by aerosol and cause laboratory-acquired infection.
Related conditions
- Vertebral osteomyelitis
- Spinal tuberculosis (Pott disease)
- Infective endocarditis
- Typhoid (enteric) fever
- Tuberculosis
- Bacterial meningitis
- Malaria
Educational information, not medical advice. For any symptom, see a health professional.
Sources: Brucellosis (World Health Organization, 2020); Brucellosis: MedlinePlus Medical Encyclopedia (MedlinePlus (U.S. National Library of Medicine), 2024).
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