Melioidosis

Overview – Melioidosis

Melioidosis is a serious infectious disease caused by Burkholderia pseudomallei, an intracellular gram-negative bacillus found in wet soil and surface water, particularly in tropical regions during the rainy season. It commonly affects immunocompromised individuals and those with chronic lung disease. Transmission occurs via percutaneous inoculation or inhalation, and the infection often presents as pneumonia with upper lobe cavitations, closely mimicking tuberculosis. Prompt diagnosis and prolonged antibiotic therapy are essential due to its potential to cause rapid sepsis and death.

Definition

Melioidosis is an infectious disease caused by Burkholderia pseudomallei, typically acquired through environmental exposure in endemic regions, leading to pneumonia, sepsis, and abscess formation.

Aetiology

• Pathogen: Burkholderia pseudomallei
• Reservoir: Soil and fresh surface water
• Seasonality: Higher incidence during the wet season
• Transmission Routes:
  • Percutaneous inoculation
  • Inhalation
• Risk Factors:
  • Immunosuppression
  • Chronic lung disease

Morphology

Macroscopic Features

• Cavitatory lesions in upper lobes of the lungs
• Cutaneous abscesses or ulcers

Microscopic Features

• Rod-shaped, gram-negative bacilli
• Fluorescent staining can be used for identification

Pathogenesis

• Intracellular pathogen: survives and replicates inside host cells
• Requires cell-mediated immunity for control
• Humoral immunity (antibody-mediated) is ineffective

Clinical Features

Typical Presentation

• Pulmonary involvement:
  • Pneumonia with cough, sputum production, and respiratory distress
  • Upper lobe cavitations (often resemble tuberculosis)
• Systemic features:
  • Pyrexia of unknown origin (PUO)
  • Chills and rigors
• Cutaneous involvement:
  • Skin ulcers and abscesses
• Complications:
  • Sepsis, which may progress to multi-organ failure and death

Diagnosis

• Definitive test: Culture of Burkholderia pseudomallei from clinical specimens
• Fluorescence staining can aid visualisation

Management

• Organism is resistant to broad-spectrum antibiotics
• Requires long-course antibiotic therapy with agents active against B. pseudomallei
• Early recognition and aggressive treatment are vital to reduce mortality

Summary – Melioidosis

Melioidosis is a life-threatening infection caused by Burkholderia pseudomallei, typically transmitted through contact with contaminated wet soil or water. It presents most commonly as upper-lobe cavitating pneumonia but can rapidly progress to sepsis. Diagnosis is confirmed by culture, and treatment requires long-term targeted antibiotics due to innate resistance. For a broader context, see our Microbiology & Public Health Overview page.