What is melioidosis and the Causes of melioidosis?

Melioidosis is a tropical infectious disease endemic to Southeast Asia and northern Australia caused by a bacterium, affecting several organs and whose treatment is complex.

Melioidosis is an infectious tropical disease in Southeast Asia and northern Australia produced by a bacterium called Burkholderia pseudomallei. This disease was first described in heroin injectors in 1912 Burma (now Myanmar) by Whitmore and Krishnashwami. Hence it is also known as Whitmore’s disease. 

Melioidosis, fatal in 50-70% of cases, can cause multiple organ diseases, the most common being pneumonia, and skin involvement. The symptoms may depend on the person’s age and even the geographical area in which the infection has occurred. Sepsis is the most severe form and has a high mortality, and the central nervous systems like involvement. It is estimated that about 90,000 people die annually from this cause, similar figures to the victims caused by dengue.

This disease has also been called the ‘Vietnam time bomb’ due to its geographical extension and incubation time, which can sometimes be very long. However, it is usually 1 to 21 days. Sometimes the bacteria can persist latently in the body for decades and not produce clinically relevant disease until years after acquiring it if the person’s defenses are diminished by processes such as diabetes or other chronic diseases.

This bacterium is transmitted by direct contact with the ground (primarily through abrasions on the skin) or by inhalation of dust or water containing the bacteria or ingesting water contaminated with it. It is more typical of rainy seasons and tropical climates and can affect thousands of affected countries. Melioidosis is more common in people between the ages of 40 and 60, especially men. It occurs more frequently in patients suffering from certain chronic diseases that cause an alteration in the body’s defense capacity against the bacteria.

One of the problems with this pathology is that its symptoms are easily confused with other diseases, so it is underdiagnosed. The number of affected could be much higher than the official figures. For the diagnosis of melioidosis, the bacteria must be identified in a culture of samples from the affected organs. After the diagnosis, it is necessary to carry out a prolonged two-phase antibiotic treatment for months. Something that is not usually easy since this bacterium is resistant to a large number of antibiotics. In cases where there is no septicemia, the prognosis is relatively good, although relapses can occur in up to 10% of cases.

In recent months, vaccines have been tested in mice with promising results, but more studies are still required to verify their level of protection in humans.

Causes of melioidosis

Melioidosis is a tropical disease caused by the bacterium Burkholderia pseudomallei (formerly called Pseudomonas pseudomallei). It is a Gram-negative type bacteria that can live both inside and outside of cells. This disease is endemic to Southeast Asia and North Australia, China, and South Asia (including India). Most cases are in Thailand, Malaysia, Singapore, and northern Australia. Isolated cases have been described outside these areas, such as Papua, Sri Lanka, parts of Africa, and the Middle East, but they have usually been travelers to endemic areas. However, a case has ever been described in people who have not traveled to these areas (such as six cases in Puerto Rico between 1982 and 2012). Similarly, some patients have been reported in the Americas, specifically in Mexico, Panama, Ecuador, Peru, El Salvador, Guyana, Brazil, Martinique, and Guadeloupe.

The bacterium is widely found in these countries in the soil and surface waters, such as in rice fields. It is more common for the disease to appear in the rainy season: 75-85% of cases are concentrated. There are about 20 annual cases per 100,000 inhabitants (more than 13,000 affected per year), as in northern Australia, although in the wettest years with many cyclones, 42 cases per 100,000 inhabitants have been described annually. Today it is the third leading cause of death from infectious disease in Thailand, after HIV and tuberculosis. Also, there may be an undetermined number of undiagnosed cases.

The bacteria are not transmitted between people or from animals to people (except in very exceptional cases). Infection is more common among paddy field workers by direct percutaneous inoculation. Water immersion or aspiration can also cause infection, as happened in the 2004 tsunami floods.

Other ways of becoming infected are inhalation or contaminated water, whether it is potable or not. Transmission by breastfeeding (from infected mother to nursing child), handling laboratory samples, or by sexual transmission is extremely rare.

Melioidosis can affect anyone, even previously healthy. Still, it is more frequent and more severe in patients with the following risk factors: diabetes, excessive alcohol consumption, chronic lung diseases (such as cystic fibrosis, especially), kidney failure chronic, nephrolithiasis (kidney stones), thalassemia (an alteration of hemoglobin) and kava (a plant that is chewed for its psychotropic properties).