Brucellosis of the Spine (Spinal Brucellosis)

Spinal brucellosis is the most common form of osteoarticular brucellosis, a zoonotic infection caused by Brucella species. It represents one of the most important causes of spondylodiscitis in endemic regions.

Causative organisms:

• Brucella melitensis (goats/sheep): Most common and most virulent for humans (responsible for greater than 90% of spinal cases)
• Brucella abortus (cattle): Milder disease
• Brucella suis (pigs): Variable severity
• Brucella canis (dogs): Rare cause of human disease

Epidemiology:

• Endemic in Mediterranean basin, Middle East, Indian subcontinent, Central Asia, Latin America
• 500,000 new cases annually worldwide
• Osteoarticular involvement: 6-12% of all brucellosis cases
• Spondylitis: Most common osteoarticular manifestation (50-60% of skeletal brucellosis)
• Males affected more than females (2:1)
• Peak incidence: 40-60 years (spinal involvement)

Brucella characteristics:

• Small, gram-negative coccobacillus
• Facultative intracellular organism (survives within macrophages)
• Slow-growing (cultures need 4-6 weeks incubation)
• Non-motile, non-spore forming
• No exotoxins or plasmids

Transmission routes:

• Ingestion: Unpasteurized milk, cheese, ice cream (most common)
• Direct contact: Through skin abrasions with infected animals/products
• Inhalation: Aerosols in laboratories, abattoirs, farms
• Rarely: Vertical transmission, sexual transmission

Pathophysiology of spinal involvement:

• Hematogenous spread from primary infection (usually intestinal)
• Brucellae lodge in vertebral metaphyseal vessels
• Initial osteomyelitis of vertebral endplate
• Spread to adjacent disc and vertebra (spondylodiscitis)
• Granulomatous inflammation with microabscess formation
• Less destruction than pyogenic infection due to granulomatous nature

Predilection for lumbar spine:

• L4-L5 most commonly affected (40-50%)
• L3-L4 second most common
• Lumbar spine involved in 70-80% of cases overall
• Cervical spine rare (less than 5%)
• Multifocal involvement in 10-20%

Systemic symptoms:

• Undulant fever (classically rises and falls - "Malta fever")
• Night sweats, malaise, fatigue
• Weight loss, anorexia
• Hepatosplenomegaly (30-50%)
• May have subacute or chronic presentation

Spinal symptoms:

• Back pain: Insidious onset, progressive, worse at night
• Localized tenderness: Over affected vertebrae
• Muscle spasm: Paravertebral muscle guarding
• Reduced range of motion: Particularly extension

Key clinical features distinguishing from TB:

• More indolent course with systemic symptoms
• Less severe destruction and deformity
• Paraspinal abscess less common and smaller
• Neurological involvement less severe
• Better response to medical treatment

Imaging Gallery

Treatment outcomes:

• Cure rate: 95% with appropriate antibiotics
• Relapse rate: 5-10% with adequate treatment (higher with monotherapy)
• Time to response: 2-4 weeks for symptom improvement
• Residual back pain: 20-30% have some long-term pain

Complications:

Prognostic factors:

• Early diagnosis improves outcomes
• Neurological involvement worsens prognosis
• Treatment delay associated with higher complication rate
• Compliance with prolonged antibiotics crucial

• Optimal regimen: Meta-analysis evidence (Skalsky, BMJ 2008) shows doxycycline-rifampicin relapses more than aminoglycoside-containing regimens, yet the all-oral doxycycline-rifampicin combination remains widely used for adherence in outpatient and limited-resource settings. The trade-off between efficacy and feasibility is unresolved for spinal disease specifically.
• Treatment duration: There is no randomised evidence defining the ideal duration for brucellar spondylitis. Practice ranges from a minimum of 3 months to 6 months or longer, individualised to clinical response, abscess and inflammatory-marker normalisation rather than a fixed endpoint.
• Role and timing of surgery: Thresholds for operating on epidural or paravertebral abscess without progressive neurology are debated; many collections resolve with antibiotics alone, but the size and response that should trigger drainage are not standardised.
• Monitoring cure and defining relapse: Serological titres can persist after microbiological cure, so distinguishing true relapse from residual antibody or non-infective mechanical back pain is difficult; the relative value of MRI, inflammatory markers and antibody assays for follow-up is not firmly established.
• Empirical therapy in dual-endemic regions: Where tuberculosis and brucellosis coexist, whether to await tissue/molecular confirmation or start empirical therapy when both are plausible remains a clinical judgement, given the very different drug regimens and durations.

Global epidemiology:

Brucellosis is the commonest bacterial zoonosis worldwide, with the heaviest burden across the Mediterranean basin, Middle East, Central Asia, the Indian subcontinent, sub-Saharan Africa and Latin America. Incidence is highly heterogeneous: many high-income countries that have eradicated bovine brucellosis (much of Western Europe, North America, Japan, Australia and New Zealand) now see almost exclusively imported cases in travellers and migrants, whereas hyperendemic regions report population incidence orders of magnitude higher. There is no implant registry for spinal infection; the relevant "registries" are national notifiable-disease surveillance systems (e.g. national public-health agencies and WHO/FAO/OIE reporting), which capture confirmed human cases and inform regional risk.

Side-by-side guidance:

Diagnostic and biosafety considerations:

Brucella is a hazard-group/risk-group 3 organism; laboratories must be alerted to the clinical suspicion so that cultures are handled in appropriate containment and incubated for the extended period required. In non-endemic settings, local laboratories may have limited experience, and serology (Rose Bengal screening with confirmatory agglutination/ELISA) plus molecular testing through reference laboratories is the mainstay. A clear travel, dietary and occupational history is the single most important step that prompts the correct test.

High- vs limited-resource practice variation:

• High-resource settings: MRI is readily available for early diagnosis and monitoring; automated blood-culture systems and PCR improve and accelerate confirmation; infectious-diseases input guides prolonged therapy and surgery is reserved for neurological deficit, instability or abscess unresponsive to antibiotics.
• Limited-resource / hyperendemic settings: Diagnosis often rests on serology and plain radiographs (Pedro Pons sign), with MRI and PCR less accessible; the doxycycline + rifampicin oral regimen is favoured for outpatient feasibility and adherence despite a higher relapse risk than aminoglycoside-containing regimens; the major public-health lever is control of animal reservoirs and pasteurisation of dairy.