Brucella – summary

• Other names – undulant fever, Malta fever, Mediterranean fever
• Zoonosis – directly or indirectly spread

Morphology & Taxonomy

• Gram -ve
• Coccobacilli
• Non motile, non sporting
• Aerobic
• Strains – B. melitensis (most common cause in humans), B. abortus, B. suis, B. ovis

Culture

• Strict aerobes
• Some strains – capnophilic ( requires 5-10% CO2 for growth )
• Simple media – slow growth, liver infusion media
• Liquid media – uniform growth
• Solid media – trypticase soya agar – small moist glistening colonies

• Casteneda method – biphasic blood culture bottle

Epidemiology

• More in areas of domesticated animals
• True worldwide prevalence unknown

Pathogenesis

• Both humoral & cell mediated immunity
• Brucella is an intracellular bacilli
• Phagocytosed by macrophages
• Supress intracellular killing & apoptosis
• Virulence factors – smooth lipopolysaccharide (LPS), ß-cyclic glucan
• TNF-alpha, IL-12 important in immunity

Clinical features

• Incubation period – 1 wk to months
• 3 types – acute, chronic, latent
• Undulating pattern
• ½ of cases – with musculoskeletal symptoms – acute monoarthritis hip/ knee
• Non specific constitutional symptoms
• Osteomyelitis involving lower thoracic & lumbar vertebrae
• Septic arthritis
• Dry cough – ¼ of patients
• Hepatosplenomegaly – ¼ of patients
• Lymphadenopathy – 10-20% patients
• Epididymo orchitis – 10% of affected men
• Depression, lethargy, lymphocytic meningoencephalitis
• Endocarditis is rare – aorta most common if involved
• Dd – Tb, EBV, Toxoplasma, CMV, HIV

Lab diagnosis

• Blood culture – casteneda method ( +ve in 30-50% cases )
• Serological methods
  • Standard agglutination test – tube agglutination test,
    • serum mixed with antigen incubated at 37°C for 24 hrs or 50°C for 18 hrs
    • Antibodies appear in 7-10 dys
    • Blocking or non agglutinating antibodies – removed by heating
  • Complement fixation
  • ELISA
  • Rapid methods – rose Bengal, rapid dipstick methods
• Skin tests

• In animals – milk ring test, microscopy, immunofluorescence, rapid tests

Treatment

• Tb to be excluded
• Streptomycin + Doxycycline
• Rifampicin/ gentamicin/ cotrimaxazole may be used

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Check out other bacteria too :-

Staphylococcus- summary
Pneumococcus- summary
Vibrio- summary
Haemophilus- summary
Bordetella- summary