Melioidosis

Introduction

Melioidosis and glanders are infectious diseases with similar clinical presentations, both caused by species of the bacterial genus Burkholderia. The two diseases differ in their geographical spread and ecology.

What is melioidosis?

Melioidosis is an uncommon tropical disease caused by the bacterium, Burkholderia pseudomallei (formerly Pseudomonas pseudomallei and Malleomyces pseudomallei). Melioidosis is endemic in South-East Asia and northern Australia, and cases also occur in the South Pacific, Africa, India, the Middle East, and Central and South America. It has the potential to produce fatal disease and is considered a potential biological warfare agent because it is highly infectious, especially by inhalation [1].

Melioidosis is also called Whitmore disease, Vietnamese time bomb, Nightcliff gardener's disease, morphia injector’s septicaemia, and paddy-field disease.

 

 

 

Who gets melioidosis?

Melioidosis predominantly occurs in people who have frequent contact with soil or surface water, such as workers in rice paddies, particularly during the rainy season. Travellers to rural areas in endemic countries may be at risk if they come into contact with contaminated soil or water, especially if they are immunosuppressed or have a chronic condition such as diabetes, liver or kidney disease, or chronic lung disease [1]. Historically, melioidosis has also been described as being transmitted via intravenous drug use, but this is now extremely rare.

How is melioidosis acquired?

B. pseudomallei can be acquired by humans and animals via contact with contaminated soil (especially through skin abrasions), inhalation of dust, and the ingestion or aspiration of contaminated water. Person-to-person transmission is very rare. The organism is categorised as a Hazard Group 3 biological agent, so specimens from patients with suspected melioidosis must be handled in a containment laboratory to reduce the risk of laboratory-acquired infection.

What are the clinical features of melioidosis?

Most cases of melioidosis in endemic areas are recently acquired (within a few days). However, the incubation period for melioidosis can range up to many years. The disease may develop following surgery, during intercurrent illness, or at times of stress years after exposure, as has been well documented in US servicemen who served in Vietnam [2]. The different presentations of the disease are discussed below.

Asymptomatic exposure

In healthy people, exposure to B. pseudomallei may be associated with asymptomatic seroconversion (the time period where antibodies develop and become detectable in the blood).

Localised infection

Localised infection with melioidosis results from direct inoculation through a skin abrasion.

• A nodule, ulcer, or abscess develops at the site of entry.
• The infection is associated with fever and muscle pain.
• It can progress to septicaemia (bloodstream infection), osteomyelitis, meningitis, and brain, liver, or spleen abscesses.

Pulmonary infection

Pulmonary infection is the most common presentation for melioidosis.

• Lung infection can range from mild bronchitis to severe pneumonia.
• Chest pain, cough, fever, headache, loss of appetite, and muscle pain are all common.
• The lung infection can become chronic and may be mistaken for tuberculosis.

Septicaemia

Septicaemia, or acute bloodstream infection, is the most severe form of melioidosis.

• It occurs mainly in people with underlying chronic conditions, such as liver or kidney disease.
• Symptoms are often non-specific but generally include fever, breathing difficulties, headache, diarrhoea, abscesses on the skin and throughout the body, muscle pain, and confusion.
• The onset of septicaemia is rapid and often leads to septic shock.
• The mortality rate for septicaemic melioidosis can exceed 80%.

Disseminated infection

In disseminated melioidosis, abscesses develop in various body sites, such as the skin, lymph nodes, muscle, brain, or internal organs (especially the liver, spleen, lung, and prostate).

• It can occur with acute or chronic melioidosis.
• Symptoms include fever, weight loss, abdominal pain, chest pain, muscle and joint pain, headache, and seizures.

What are the complications of melioidosis?

Melioidosis can be life-threatening. The risk is increased with:

• More extensive or severe disease
• Comorbidities such as chronic diseases (diabetes, chronic lung disease, the liver or kidney disease) or immunosuppression.

Complications of melioidosis include:

• Sepsis
• Organ failure
• Pneumothorax (collapsed thorax)
• Cardiac tamponade (fluid buildup in the pericardial area)
• Recurrence of infection.

How is melioidosis diagnosed?

Culture from blood, sputum, or other infected sites will confirm the diagnosis.

• A full screen should be sent for culture (blood, sputum, urine, throat swab, and any aspirated pus). Selective media increase the yield from non-sterile sites.
• Serology is only of benefit in patients from non-endemic areas or if seroconversion can be demonstrated.
• Laboratories must be informed of the suspected diagnosis for two reasons. Firstly, the organism may be dismissed as an environmental contaminant by the unwary, and secondly, to ensure the use of appropriate media and laboratory containment.

What is the differential diagnosis for melioidosis?

Any infectious disease causing fever, headache, muscle pain with pneumonia, abscesses, or skin involvement could be included in the differential diagnoses for melioidosis, including:

• Tuberculosis
• Staphylococcal disease with sepsis
• Invasive Klebsiella infection
• Anthrax
• Tularaemia
• Cat scratch disease
• Glanders
• Plague.

What is the treatment for melioidosis?

Antibiotics are the mainstay of treatment for melioidosis. Currently, ceftazidime is the treatment of choice during the acute phase.

• Antibiotics are given intravenously initially for the first 10–14 days.
• The intravenous antibiotics are then changed to oral treatment, usually trimethoprim–sulphamethoxazole, for 12–20 weeks.
• Continuous antibiotic treatment is required for several months in order to prevent relapse.
• Severe cases of melioidosis may require admission to an intensive care unit for supportive therapy.
• Abscesses may require surgical drainage.

Prevention of melioidosis

There is currently no effective vaccine for melioidosis. The risk of exposure to B. pseudomallei can be minimised by:

• Avoiding contact with soil and standing water in endemic areas — this especially applies to people with skin wounds or chronic health conditions
• Agricultural workers in endemic areas wearing rubber boots when working
• Appropriate use of personal protective measures by healthcare and laboratory staff.

What is the outcome of melioidosis?

The septicaemic form of melioidosis carries a very high mortality risk (90%) if not appropriately treated. There is also the potential for the disease to recur in patients many years after the initial infection, including in patients who were asymptomatic originally.

Scarring may occur from chronic skin lesions.