Melioidosis

Definition

Melioidosis is an infectious disease of humans and animals caused by a gram-negative bacillus found in soil and water. It has both acute and chronic forms.

Description

Melioidosis, which is sometimes called Pseudomonas pseudomallei infection, is endemic (occurring naturally and consistently) in Southeast Asia, Australia, and parts of Africa. It was rare in the United States prior to recent immigration from Southeast Asia. Melioidosis is presently a public health concern because it is most common in AIDS patients and intravenous drug users.

Causes & symptoms

Melioidosis is caused by Pseudomonas pseudomallei, a bacillus that can cause disease in sheep, goats, pigs, horses, and other animals, as well as in humans. The organism enters the body through skin abrasions, burns, or wounds infected by contaminated soil; inhalation of dust; or by eating food contaminated with P. pseudomallei. Person-to-person transmission is unusual. Drug addicts acquire the disease from shared needles. The incubation period is two to three days.

Chronic melioidosis is characterized by osteomyelitis (inflammation of the bone) and pus-filled abscesses in the skin, lungs, or other organs. Acute melioidosis takes one of three forms: a localized skin infection that may spread to nearby lymph nodes; an infection of the lungs associated with high fever (102°F/38.9°C), headache, chest pain, and coughing; and septicemia (blood poisoning) characterized by disorientation, difficulty breathing, severe headache, and an eruption of pimples on the head or trunk. The third form is most common among drug addicts and may be rapidly fatal.

Diagnosis

Melioidosis is usually suspected based on the patient's history, especially travel, occupational exposure to infected animals, or a history of intravenous drug. Diagnosis must then be confirmed through laboratory tests. P. pseudomallei can be cultured from samples of the patient's sputum, blood, or tissue fluid from abscesses. Blood tests, including complement fixation (CF) tests and hemagglutination tests, also help to confirm the diagnosis. In acute infections, chest x rays and liver function tests are usually abnormal.

Treatment

Patients with mild or moderate infections are given a course of trimethoprim-sulfamethoxazole (TMP/SMX) and ceftazidime by mouth. Patients with acute melioidosis are given a lengthy course of ceftazidime followed by TMP/SMX. In patients with acute septicemia, a combination of antibiotics is administered intravenously, usually tetracycline, chloramphenicol, and TMP/SMX.

Prognosis

The mortality rate in acute cases of pulmonary melioidosis is about 10%; the mortality rate for the septicemic form is significantly higher (slightly above 50%). The prognosis for recovery from mild infections is excellent.

Prevention

There is no form of immunization for melioidosis. Prevention requires prompt cleansing of scrapes, burns, or other open wounds in areas where the disease is common and avoidance of needle sharing among drug addicts.

Key Terms

Osteomyelitis

An inflammation of bone or bone marrow, often caused by bacterial infections. Chronic melioidosis may cause osteomyelitis.

Septicemia

Bacterial infection of the bloodstream. One form of melioidosis is an acute septicemic infection.

Further Reading

For Your Information

Books

• "Bacterial Diseases: Melioidosis." In The Merck Manual of Diagnosis and Therapy, vol. I, edited by Robert Berkow, et al. Rahway, NJ: Merck Research Laboratories, 1992.
• "Ceftazidime." In Nurses Drug Guide 1995, edited by Billie Ann Wilson, et al. Norwalk, CT: Appleton & Lange, 1995.
• Pollock, Matthew. "Infections Due to Pseudomonas Species and Related Organisms." In Harrison's Principles of Internal Medicine, edited by Anthony S. Fauci, et al. New York: McGraw-Hill, 1998.
• "Trimethoprim-sulfamethoxazole." In Nurses Drug Guide 1995, edited by Billie Ann Wilson, et al. Norwalk, CT: Appleton & Lange, 1995.

Gale Encyclopedia of Medicine. Gale Research, 1999.