Melioidosis is an infectious disease resulting from contact with Burkholderia pseudomallei, a bacterium that thrives in soil and water, particularly in tropical climates. While many people exposed to the bacterium never develop symptoms, it can cause a range of illnesses in others. The disease is also known as Whitmore’s disease, named after Captain Alfred Whitmore, who first identified the causative bacteria.
Transmission and Geographic Distribution
The primary route of infection involves direct contact with contaminated soil and water. The B. pseudomallei bacterium enters the body through breaks in the skin, such as cuts or scrapes. Inhalation of contaminated dust or water droplets is another significant mode of transmission, especially during and after heavy rainfall or storms which can aerosolize the bacteria. Ingesting contaminated water is a less common but recognized pathway for infection.
The disease is most prevalent in specific regions, with Southeast Asia (particularly Thailand, Malaysia, and Singapore) and northern Australia considered endemic areas. Cases have also been identified in other parts of Asia, the Pacific, the Americas, and the Middle East. Person-to-person transmission is exceedingly rare.
Signs and Symptoms of Infection
Melioidosis is often called “the great mimicker” because its symptoms are incredibly diverse and can resemble those of other common illnesses like tuberculosis. The presentation of the disease depends on the location of the infection within the body, and it can manifest in either acute or chronic forms. Symptoms appear one to four weeks after exposure, but in some cases, the bacterium can remain dormant for years before causing illness.
A localized infection may appear as a nodule, ulcer, or abscess on the skin at the point of entry, often accompanied by fever, swelling, and muscle aches in the affected area. When the infection is concentrated in the lungs, a condition known as pulmonary melioidosis, it can cause a cough, chest pain, high fever, headache, and a loss of appetite. This is the most common form of the disease and can range from mild bronchitis to severe pneumonia.
If the bacteria enter the bloodstream, it can lead to septicemia. Symptoms of a bloodstream infection are often severe and include high fever, headache, fatigue, difficulty breathing, and abdominal or joint pain. Patients may also experience disorientation and confusion. In some instances, the infection can spread throughout the body, a state referred to as disseminated infection, causing abscesses to form in various internal organs. This form may present with fever, weight loss, and pain in the muscles, joints, chest, or stomach.
Underlying Risk Factors
While anyone exposed to B. pseudomallei can become ill, certain underlying health conditions increase an individual’s susceptibility to developing a severe infection. The most significant risk factor is diabetes mellitus, which is present in a large percentage of patients.
Other predisposing conditions include chronic organ diseases, such as liver disease, chronic kidney disease, and chronic lung diseases like COPD. The blood disorder thalassemia is also a recognized risk factor. Conditions that weaken the immune system, including cancer or heavy alcohol use, also make a person more vulnerable to a severe infection.
Diagnosis and Treatment
A definitive diagnosis requires laboratory testing to isolate and identify B. pseudomallei from clinical samples like blood, urine, sputum, or pus from a lesion. Because of the risks in handling the bacterium, laboratory personnel must be properly trained and may use specialized culture media to grow the organism.
Treatment for melioidosis occurs in two distinct stages to ensure the complete removal of the bacteria and prevent a relapse. The first stage is the intensive phase, which involves administering intravenous (IV) antibiotics for a minimum of two weeks, though it can extend to eight weeks or more for severe cases. Commonly used IV antibiotics include ceftazidime or meropenem.
Following the intensive phase, patients move to an eradication phase, which involves taking oral antibiotics for three to six months. The standard medication for this phase is often trimethoprim-sulfamethoxazole. Completing the full course of oral antibiotics is necessary to prevent the disease from recurring, as relapses can happen if treatment is cut short.
Prevention Strategies
Preventing melioidosis involves avoiding direct contact with contaminated soil and water, especially in endemic regions. Individuals, particularly those with underlying health conditions that make them more susceptible, can reduce their risk by taking the following precautions:
- Wear waterproof boots and gloves during activities that involve contact with soil, such as farming or gardening.
- Protect any open wounds, cuts, or scrapes on the skin with waterproof dressings to prevent bacteria from entering the body.
- Avoid exposure to dust and stay indoors during heavy rains or storms when the bacteria are more likely to be in the air.
- Drink boiled or properly chlorinated water to prevent ingestion-related transmission.