General Information - melioidosis

What is melioidosis?

Melioidosis is the name given to any infection with the organism Burkholderia pseudomallei. The organism is common in the environment in tropical regions, where it is found in soil, mud and water, especially that of rice paddies. Naturally occurring infection is therefore primarily a disease of the tropics. Many animal species are susceptible including mammals, birds, and even reptiles. Most human cases do not arise from animal contact however, rather from environmental exposure, and may be rapidly fatal.

What is its bioterrorism potential?

The organism is not known to have been the subject of weaponisation attempts. However, it could be a potential agent for bioterrorism as it can infect people by many diverse routes, is able to survive for long periods in the environment and can cause rapidly fatal infections. A likely route would be airborne spread.

How do you catch melioidosis?

Naturally acquired infection usually occurs by inoculation through cuts and abrasions, or sometimes by aspiration or inhalation. In endemic areas, many cases are associated with soil contact, i.e. rice farmers or other agricultural workers. Ingestion of contaminated water is also a possible route. In a deliberate release situation, the most likely route would be inhalation. Most cases occur in people with some underlying medical condition such as diabetes, chronic kidney or liver disease, or long term steroid treatment. Person-to-person spread can occur but is extremely rare.

How long can you have the infection before developing symptoms?

This is extremely variable, and ranges from two days to many years - latent intervals as long as 62 years have been reported in naturally occurring melioidosis. For many naturally-occurring cases the exact time of exposure is not known, except following obvious trauma or "near-drowning".

What are the symptoms?

Melioidosis can present in a variety of ways:

• Lung infection – mild bronchitis to severe pneumonia. Symptoms include high fever, cough, and severe chest and muscle pain.
• Bloodstream infection ('blood poisoning' or 'septicaemia') – this is a very severe form of disease which is often fatal. Symptoms generally include high fever, headache and delirium, and difficulty breathing, and later low blood pressure and failure of vital organs.
• Acute localised infection of skin and soft-tissues following trauma and inoculation.
• Chronic infection – any organ or part of the body can be infected and so symptoms are very varied; for example, joint infection, swollen lymph nodes, and abscesses in places such as the liver, spleen, and prostate gland.

How can melioidosis be treated?

Untreated severe disease is nearly always fatal, whereas localised infections have a much lower fatality rate (approximately 5%). Once the disease has been diagnosed correctly, antibiotic treatment may reduce the mortality of severe disease to approximately 40%. Antibiotic treatment must continue for prolonged periods (five to six months) to prevent the disease recurring.

How can melioidosis be prevented?

There is no vaccine. Person-to-person spread is rare but can occur, so cases need to be isolated. Prevention of disease in endemic areas is difficult because of the environmental nature of the organism. The value of prophylactic antibiotics in people who have been exposed to a deliberate release is unknown, although there is evidence of a partial protective effect in experimental animals.

How common is melioidosis?

In highly endemic areas such as the north-east of Thailand and northern Australia, melioidosis is a significant cause of disease, and in recent years it has become apparent that other areas of Asia, including the Indian sub-continent, have more disease than was previously recognised.

In temperate areas, disease is very rare and is almost always imported, i.e. acquired during travel to an endemic area. In the United Kingdom, 22 travel-associated cases were diagnosed in the decade 1997-2006, with exposures in Thailand, Viet Nam, India, and Bangladesh.

Last reviewed: 11 June 2010