Melioidosis

Melioidosis, also known as pseudoglanders and Whitmore's disease (after Capt Alfred Whitmore) is an uncommon infectious disease caused by a Gram-negative bacterium, Burkholderia pseudomallei, found in soil and water. It exists in acute and chronic forms. more...

The causative organism, Burkholderia pseudomallei, was thought to be a member of the Pseudomonas genus and was previously known as Pseudomonas pseudomallei. This organism is phylogenetically related closely to Burkholderia mallei, the organism that causes glanders. Another closely-related but less virulent bacterium is found in Thailand and is called Burkholderia thailandensis.

Melioidosis is endemic in parts of south east Asia and northern Australia. Its true extent has not been completely defined but it has been noted before in Africa, India, parts of the Middle East and Central and South America. It affects humans as well as other animals such as goats, sheep, horses and cattle. The mode of infection is usually either through an infected laceration or burn or through inhalation of aerosolized B. pseudomallei.

There has also been interest in melioidosis because it has the potential to be developed as a biological weapon.

Symptoms and signs

Patients with chronic or latent melioidosis may be symptom free for decades.

A patient with active melioidosis usually presents with fever. There may be pains in multiple sites around his/her body due to bacteremia and abscess formation. Patients with melioidosis usually have risk factors for disease, such as diabetes, thalassemia or renal disease. However, otherwise healthy patients, including children, may also get melioidosis.

If there is pulmonary involvement, there may be signs and symptoms of pneumonia.

If hepatic or splenic abscesses are present, the patient may present with abdominal pain. If there are brain abscesses present, the patient may present with neurological signs and symptoms. An encephalomyelitis syndrome is recognised in northern Australia.

Melioidosis may also cause osteomyelitis and present with bony pain.

In Thailand, parotid abscesses in children are common.

Diagnosis

A definite history of contact with soil or animals may not be elicited as melioidosis can be dormant for many years before becoming acute. Attention should be paid to a history of travel to endemic areas in returned travellers. Patients with diabetes mellitus often have a more serious presentation of melioidosis.

A definitive diagnosis can be made by growing B. pseudomallei from blood cultures or from pus aspirated from an abscess. Culture mediums may need to have additional agents added to facilitate the growth of B. pseudomallei.

There is also a serological test for melioidosis, but this is not commercially available in some countries. A high background titre may complicate diagnosis.

If clinically indicated, CT scans (or, in some cases, ultrasound scans) of the thorax and abdomen are useful to investigate for the presence of abscesses and to rule out other diseases.

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