Melioidosis: causes, symptoms, diagnosis, and treatment

Melioidosis is a special infection caused by Burkholderia pseudomallei, mainly in rodents. Occasionally, the disease can be transmitted to humans, causing infections in the lungs and other organs. Skin infections are often manifested by abscesses.


Causes

The disease occurs mostly in the rainy season. Burkholderia pseudomallei is a saprophytic parasite and is a small, polymorphic, Gram-negative, aerobic bacterium, and can be isolated in soil, vegetables, and water in endemic areas. Humans are mainly infected by inhalation or wounded skin.


Signs and Symptoms

The incubation period is as short as 3 days and as long as several years. The disease can be acute, subacute, and chronic. In acute cases, patients have high fever, pneumonia, and gastroenteritis, and often die within few days. Most cases are subacute, persisting for one to several weeks. If the primary lesion is in the skin, local abscesses are formed, lymphangiitis, lymphadenitis, and sepsis occur rapidly, and multiple abscesses occur in the subcutaneous muscle, liver, spleen, and lung. If infections are caused by inhalation, the initial symptoms are mainly in the lung, mostly fever and diffuse suppurative lesions, many miliary abscesses may be present in the internal organs, and various clinical symptoms are present. In chronic cases, pulmonary symptoms and visceral metastatic small abscesses are more common, often accompanied by fever, failure, and other systemic symptoms, and severe urticaria may be present. In Thailand, acute suppurative parotitis is a common manifestation of localized melioidosis in children. The disease may relapse after a long incubation period.


Diagnosis

In endemic areas, diagnosis can be based on a history of exposure to the infected animals, clinical symptoms, and bacteriological examination. Positive results in the indirect hemagglutination assay and complement fixation test with heat-resistant polysaccharide antigen or Burkholderia pseudomallei antigen preparations, especially the significantly elevated antibody titers, can assist in the definitive diagnosis. Positive results often appear in 1 week after acute onset, and about 90% of patients have positive results in 2 - 5 weeks.


Treatment

Systemic antibiotics are appropriate. Most of the infections respond well to tetracycline at a dose of 2 - 3g/d for 1 - 3 months until the lesions subside. Sulfonamides such as sulfamethoxazole and third-generation cephalosporin antibiotics such as ceftazidime are also effective and can be used in combination with tetracycline. Most strains are sensitive to new antibiotics such as ceftazidime, piperacillin-tazobactam, imipenem, and amoxicillin-clavulanic acid. Drug susceptibility test is recommended, and empirical therapy can be performed prior to the results of drug susceptibility test. After adequate antibiotic treatment, incision and drainage are required for the abscesses. Antibiotic treatment should persist for longer in patients with osteomyelitis and multiple abscesses.