Melioidosis is an infectious disease of humans and animals resulting from infection with bacteria found in the soil and water (Burkholderia pseudomallei). Melioidosis is an important endemic disease in the hot wet tropics and sub-tropics of Southeast Asia, South Asia, and especially northern Australia. Sporadic cases are increasingly reported from other countries in Asia, Africa, and the Americas.
Pneumonia with multiple abscesses is the most common result of this infection. In resource-poor endemic countries, mortality may reach 40% but falls to 10% in countries where rapid laboratory diagnosis, appropriate antibiotics, and state-of-the-art intensive care therapy are available.
Mode of Transmission
Transmission occurs when bacteria found in infected soil or water enter the feet through small cuts or puncture wounds; it can also occur through inhalation and aspiration, especially in association with recent rainfall and severe weather events (tsunami lung) and with spray from helicopter blades. Drinking contaminated water is not an important mode of transmission.
The incubation period ranges from 1 to 21 days for acute symptoms. In 11%, defined as chronic cases, symptoms have been present for more than 2 months. In 4% of cases, reactivation of latent infection presents months or years after infection.
Epidemiology and Distribution
Melioidosis primarily affects persons who are in regular contact with soil and water. The majority of cases in Thailand are in rice farmers who work without protective footwear.
In the Top End of the Northern Territory in Australia and in northeastern Thailand, annual incidence rates reach 50 cases per 100,000 people. Melioidosis is the third-most common cause of death from infectious disease in northeastern Thailand, exceeded only by HIV infection and tuberculosis. Malaysia, Singapore, Vietnam, Cambodia, and Laos are also established regions of endemic disease. The endemic zone extends to areas of the Indian subcontinent including Bangladesh and India, and to southern China, Hong Kong, Taiwan, and various Pacific and Indian Ocean islands. Sporadic cases have been reported in the Americas (Puerto Rico, Honduras, Ecuador, Guadeloupe, Aruba, and Brazil) and in Africa (Nigeria, Gambia, Kenya, Uganda, and Madagascar), but the extent of the disease in the Americas and in Africa is uncertain.
In the major endemic areas, melioidosis is seasonal. In northern Australia and Thailand, most infections occur during the monsoon season.
Melioidosis is rare among travelers. Most cases have been associated with rural travel in known endemic Asian countries, rarely in African and American countries. Implied sources of infection include penetrating wounds in the foot from a thorn or a nail, camping in the rainy season in northern Australia, working barefoot on a farm in the Philippines, and walking in mud in Martinique during heavy rains that followed Hurricane Tomas. In most cases, however, the source of infection was unknown. Most had known predisposing personal risk factors for melioidosis. With the prevalence of diabetes projected to increase dramatically in many countries, numbers of imported cases of melioidosis may increase.
Environmental risk factors for melioidosis include exposure to soil and ground water, especially in the monsoon season and during severe weather events.
Predisposing personal risk factors for melioidosis (risk groups) include people with diabetes, heavy alcohol use, chronic pulmonary disease, chronic renal disease, thalassemia, glucocorticoid therapy, and cancer. Individuals in these risk groups are at greater risk of acquiring meliodosis and of death. HIV infection does not seem to be a risk factor.
The symptoms can range from a localized lesion at an inoculation site with no systemic manifestations to overwhelming sepsis and death. Clinical patterns differ between endemic areas. Host risk factors are thought to be important in determining the severity of the infection.
- Typical presentation: Pneumonia with fever, cough, sputum, and shortness of breath is the most common presentation in adults with acute or chronic melioidosis. High fever and prostration without respiratory symptoms suggest septicemia, which may be rapidly fatal.
- Other common presentations, often in association with pneumonia, include septic or ulcerative skin lesions, abscesses in the parotid gland, prostate gland, or other internal organs, arthritis and osteomyelitis, and encephalomyelitis with muscular weakness and cranial nerve palsies.
Travelers with personal risk factors who intend travel to the major endemic areas should be advised to wear thorn-proof footwear when walking in rural areas or in mud, especially in the rainy season. There is no vaccine.
Some authorities recommend that residents of endemic countries who are in a risk group should stay indoors during periods of heavy wind and rain, when aerosolization of B. pseudomallei is possible. In the great majority of travelers who acquired melioidosis, the source and routes of infection are unknown, so it is uncertain how relevant this advice would be, unless perhaps for a traveler who chose to adopt a rural life style.
Need for Medical Assistance
Any traveler with typical or suggestive symptoms and with a risk factor for exposure to melioidosis should seek medical assistance immediately. This is especially important for a traveler who falls into one of the risk groups for whom early diagnosis and prompt treatment may be vital. Advise the health care provider of the travel itinerary, activities, and the possibility of melioidosis.
Fatal melioidosis is extremely unlikely in a previously healthy person, provided the diagnosis is made early, an appropriate combination of antibiotics is commenced, and intensive care therapy is available.