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Neurobrucellosis: Comprehensive Review

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1. DEFINITION

• Goldman-Cecil Medicine, 29th Ed. (Chapter 286)
• Harrison's Principles of Internal Medicine, 22nd Ed. (Chapter 174)

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2. EPIDEMIOLOGY

Global Burden

• Brucellosis affects >500,000 people annually worldwide across 100 countries; true incidence is estimated at 10–25× reported figures due to underdiagnosis.
• Brucella melitensis (sheep, goats, camels) is the most common cause of human disease globally.
• B. abortus (cattle), B. suis (pigs), and B. canis (dogs) account for remaining cases.

Geographic Distribution

• Highest burden: Mediterranean littoral (Middle East, North Africa), Arabian Gulf, Latin America, China, Indian subcontinent, Central Asia.
• Turkey has the highest published research output on neurobrucellosis over 30 years (bibliometric analysis, PMID 39381075).
• In the United States, cases have fallen from >6,000 in 1947 to 80–120/year, concentrated in Texas, California, Arizona, and Florida — mostly occupational or food-associated.

Neurobrucellosis-Specific

• Neurological involvement occurs in approximately 1.7–10% of brucellosis cases (most sources cite ~4%).
• Can occur at any stage: acute, subacute, or chronic brucellosis.
• Children may present differently: fever, nausea, vomiting, convulsions, papilledema, and sensorineural hearing loss are significantly more prevalent in pediatric patients than adults.
• B. ceti (from dolphins/porpoises) can also cause neurobrucellosis in humans.

Risk Factors

• Consumption of unpasteurized dairy products (cheese, milk — especially from goats/sheep)
• Occupational exposure: slaughterhouse workers, farmers, veterinarians, dairy workers, laboratory workers
• Travel to endemic regions

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3. PATHOPHYSIOLOGY

Pathogen Entry & Dissemination

1. Translocates through intestinal mucosa or respiratory epithelium.
2. Is phagocytosed by macrophages and dendritic cells — forming granulomas in regional lymph nodes.
3. If host defenses are overwhelmed → bacteremia (incubation period 2–4 weeks).
4. During bacteremia, free Brucella organisms are phagocytosed by macrophages in the spleen, liver, and bone marrow, forming noncaseating granulomas that serve as persistent infection reservoirs.

Immune Evasion Mechanisms

• Its lipopolysaccharide (LPS) differs from typical Gram-negative bacteria — minimal activation of TLR4, and resistance to complement activation.
• Deploys a protein that interferes with TLR signaling.
• ~10% of phagocytosed organisms survive acidification and lysosome fusion → form an endosomal Brucella-containing vacuole (persistent reservoir).
• Replicates by intercepting endoplasmic reticulum–Golgi traffic.
• Outer membrane proteins Omp25/Omp31 mediate direct interactions with mammalian cells.
• Other virulence factors: catalase, superoxide dismutase, alkyl hydroperoxide reductase, nitric oxide reductase.

Neurological Pathogenesis

• No bacterial toxins have been identified; tissue damage is driven by the host innate immune inflammatory response.
• Brucella induces production of proinflammatory cytokines and metalloproteinases → tissue damage.
• CNS invasion likely occurs via infected monocytes/macrophages acting as a "Trojan horse" — this is why bactericidal agents with CNS penetration are critical.
• Mechanisms of neurological injury:
  • Direct invasion: meningitis, encephalitis, myelitis, abscess
  • Vascular inflammation: vasculitis → ischemic or hemorrhagic stroke, sinus thrombosis
  • Immune-mediated demyelination: similar to MS-like picture
  • Granuloma formation: in brain parenchyma or spinal cord
• Goldman-Cecil Medicine (Chapter 286)

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4. CLINICAL FEATURES

General Brucellosis Presentations (Background)

• Insidious or acute onset; classic undulant (relapsing) fever, malaise, night sweats, arthralgias, myalgias, weight loss.

Neurobrucellosis Manifestations

• Meningitis in neurobrucellosis is described as "subacute or chronic" and "accompanied by other manifestations including encephalitis, polyradiculitis, and myelitis." — Goldman-Cecil Medicine, Chapter 397 (Zoonotic Bacterial Meningitis)
• Several cases of stroke in children with neurobrucellosis are documented. — Bradley and Daroff's Neurology in Clinical Practice

Pediatric Neurobrucellosis (distinct pattern)

• More acute/less chronic course.
• Fever, nausea/vomiting, fatigue, abdominal pain more prevalent.
• Convulsions, papilledema, sensorineural hearing loss, ascites significantly more common than in adults.
• (Tajerian et al., 2024 — systematic review and meta-analysis, PMID 35930502)

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5. EXAMINATION

General Physical Examination

• Fever (may be undulant/relapsing)
• Lymphadenopathy, hepatomegaly, splenomegaly
• Musculoskeletal tenderness (sacroiliitis, spondylitis)
• Orchitis in males

Neurological Examination

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6. INVESTIGATIONS

Microbiological

• Positive in 10–30% of acute brucellosis (up to 85% with B. melitensis).
• Sensitivity decreases with disease duration.
• ⚠️ Alert the lab: Brucella is a biosafety hazard; longer incubation may be required.

• Positive in ~45% of patients with meningitis.
• Bone marrow culture more sensitive than blood culture in B. melitensis infection.

• Available from blood, CSF, and tissue.
• Higher sensitivity than culture; useful in culture-negative or partially treated cases.

Serological Testing

• Most widely used.
• Detects antibodies to B. abortus antigen (cross-reacts with B. suis, B. melitensis; NOT B. canis).
• Significant: ≥4-fold rise in titer over 2 weeks.
• Presumptive positive: titer ≥1:160 in endemic / ≥1:80 in non-endemic areas.
• False positives: Vibrio cholerae, Francisella tularensis, Yersinia enterocolitica infections; cholera vaccination.

• Brucella-specific antibodies in CSF are important for diagnosis of neurobrucellosis.

• Detects non-agglutinating antibodies (useful in chronic brucellosis where SAT may be negative).

• Modified SAT used by the U.S. CDC.

• Requires B. canis or B. ovis antigen specifically.

CSF Analysis (key for neurobrucellosis)

Neuroimaging

• May be normal in early disease.
• Findings include: white matter changes, leptomeningeal enhancement, cerebral/cerebellar lesions, periventricular demyelination, hydrocephalus, spinal cord signal changes, vascular lesions.
• Demyelinating plaques may mimic multiple sclerosis.

• Less sensitive but useful for hydrocephalus, hemorrhage, or abscess.

Diagnostic Criteria for Neurobrucellosis (Soares et al. 2023, PMID 37093043)

1. Symptoms/signs suggestive of neurological involvement
2. CSF analysis showing abnormality
3. Positive Brucella serology or culture (blood/CSF/tissue)
4. Response to specific antibiotic therapy with significant CSF improvement

Other Investigations

• CBC: leukopenia, anemia, thrombocytopenia
• LFTs: elevated transaminases (hepatic involvement)
• ESR/CRP: elevated
• Bone marrow biopsy: culture in difficult cases

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7. TREATMENT

Principles

• Penetrate intracellularly (where Brucella resides)
• Have low toxicity for prolonged courses
• Are bactericidal (essential for CNS and endocarditis)

CNS Disease — Treatment Regimens

"Focal neurologic disease due to Brucella species requires prolonged treatment (i.e., for 3–6 months), usually with ceftriaxone supplementation of a standard regimen."

• Neurobrucellosis: Doxycycline 100 mg IV/PO BD + rifampin 600–900 mg PO daily + ceftriaxone 2 g IV BD → treat until CSF normalizes.

• The benefit of corticosteroids for neurobrucellosis is unproven.
• A Jarisch-Herxheimer-like reaction may occur at treatment initiation — acute febrile response with headache and myalgias, lasting <24 hours. Monitor closely.

Evidence-Based Update (Systematic Review & Meta-Analysis, Tajerian et al. 2024, PMID 35930502)

• Meta-analysis of 448 patients from 5 studies:
• IV ceftriaxone-based regimens showed a moderate positive effect over purely oral regimens in reducing treatment duration (SMD 0.428, 95% CI −0.63 to −0.22).
• Recommendation: Initiate treatment with IV ceftriaxone in combination with oral therapy.

Standard (Non-CNS) Adult Regimen — for context:

Corticosteroids

• Adjunctive corticosteroids: role is not proven but considered in severe neurobrucellosis with cerebral edema, vasculitis, or severe inflammatory disease.
• Future research on the role of steroids is highlighted as a priority (bibliometric analysis, PMID 39381075).

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8. PROGNOSIS

• Good if treated early — the majority recover completely without sequelae.
• Prolonged treatment (3–6 months for CNS disease) is essential to prevent relapse.
• Relapse occurs in 5–10% of cases of brucellosis overall; CNS disease has higher risk with inadequate therapy.
• Potential sequelae: hearing loss, cognitive impairment, motor deficits, psychiatric disorders.
• Mortality from brucellosis is rare (<2%) but higher in endocarditis and severe neurobrucellosis.

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9. PREVENTION

• Pasteurization of dairy products
• Animal vaccination programs
• Protective equipment for occupational exposures (slaughterhouses, veterinary work)
• Avoidance of undercooked meat and raw milk products
• Laboratory biosafety precautions when handling cultures

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Key Sources