is an infectious disease caused by a gram-negative bacterium called Burkholderia pseudomallei. Most people exposed to B. pseudomallei experience no symptoms, but complications can range from fever and skin changes to pneumonia, abscesses, and septic shock, which can be fatal.
Approximately 10% of people with melioidosis develop symptoms that last longer than two months, termed “chronic melioidosis”.
Melioidosis is a serious and often underdiagnosed infectious disease caused by the environmental bacterium Burkholderia pseudomallei.
It’s sometimes called “Whitmore’s disease” and is endemic to tropical and subtropical regions, especially Southeast Asia, northern Australia, and increasingly parts of India.
Melioidosis—caused by Burkholderia pseudomallei—has seen a surge of research interest recently, especially due to its expanding global footprint and potential as a biothreat.
Recent advances:
Emerging infections with Melioidosis—caused by Burkholderia pseudomallei—has seen a surge of research interest recently, especially due to its expanding global footprint and potential as a biothreat. —a highly pathogenic, Gram-negative β-proteobacterium.
B. pseudomallei is a saprophyte found in soil, groundwater, stagnant streams, rice paddies, and ponds.
Although melioidosis is mainly endemic in Southeast Asia and northern Australia, it is also increasingly reported in regions outside the Asia-Pacific region including India, Mauritius, the Americas, and Africa.
Melioidosis can present as an acute, subacute, or chronic process.
Disease manifestations
include subclinical infections, localized abscesses, severe pneumonia, and fulminant sepsis.
Case fatality rates ranged from 19 to 36% in endemic areas. Although the epidemiology and routes of transmission are not yet fully understood, it is believed that melioidosis is acquired through contact with contaminated soil and water by percutaneous inoculation, inhalation of aerosols, and ingestion.
The incubation period of melioidosis varies widely from two days to 62 years. Human cases are often spatially and temporally clustered, following heavy rains and winds with resultant human exposure to soil and water B. pseudomallei also causes melioidosis in a wide range of animals in endemic areas. In Hong Kong, melioidosis is an endemic disease not only in humans but also in captive marine mammals and birds, including bottlenose dolphins,
California sea lions, pilot whales, and zebra
Transmission & Risk Factors.
B. pseudomallei thrives in soil and surface water. Infection typically occurs through:• Inhalation of contaminated dust or water droplets• Ingestion of contaminated water or food• Direct contact with contaminated soil or water via skin abrasions or woundsHigh-risk groups include:• People with diabetes, chronic kidney or lung disease, cancer, or alcohol use disorder• Farmers, construction workers, and others exposed to muddy soil or floodwaters
Clinical Manifestations
Melioidosis is known for its wide spectrum of presentations:• Localized infection: Skin ulcers, abscesses• Pulmonary infection: Cough, chest pain, high fever—often mistaken for TB-Tuberculosis & Chest Diseases
Localized Skin Infections. Swelling, redness, and ulceration around a woundAbscess formationPulmonary (Lung) InfectionCough, often with mucus or phlegm. Chest pain. Fever. Difficulty breathing
Septicemia (Blood Infection)
High fever and chills.
Abdominal discomfort.
Confusion or dizziness.
Muscle or joint pain
Disseminated Infection
Abscesses in multiple organs (liver, spleen, lungs).
Weight loss and fatigueMuscle aches and joint pain.
Disseminated infection: Sepsis, organ abscesses (liver, spleen, prostate), joint and bone involvement, neurological symptoms.
Symptoms may appear within 1–3 weeks, but latent infections can emerge months or even years later.
Predisposing factors:
Diabetes mellitus is one of the most important risk factors in developing melioidosis.
The disease should be considered in anyone who has spent time in endemic areas who develops a fever, pneumonia, or abscesses in their liver, spleen, prostate, or parotid gland. Latent infections as pseudomallei can remain latent in the human body for up to 29 years until it is reactivated during human immunosuppression or stress response. However, the site of bacteria during latent infection and the mechanism by which they avoid immune recognition for years are both unclear.
Amongst mechanisms suggested are: residing in the nucleus of the cell to prevent being digested, entering a stage of slower growth, antibiotic resistance, and genetic adaption to the host environment.
Granulomas (containing neutrophils, macrophages, lymphocytes, and multinucleated giant cells) formed at the infection site in melioidosis have been associated with latent infection in humans.
Diagnosis & Treatment
Diagnosis: Blood or abscess fluid cultures are the gold standard.
Misdiagnosis is common.
Culture Microscopy. By microscopy,
B. pseudomallei is seen as gram-negative and rod-shaped, with bipolar staining similar in appearance to a safety pin.
Bacteria can sometimes be seen directly in clinical samples from infected people; however, identification by light microscopy is neither specific nor sensitive. Immunofluorescence microscopy is highly specific for detecting bacteria directly from clinical specimens, but has less than 50% sensitivity. Imaging
Various imaging modalities can also help with the diagnosis of melioidosis.
In acute melioidosis with the spreading of the bacteria through the bloodstream, the chest X-ray shows multifocal nodular lesions.
It may also show merging nodules or cavitations.
For those with acute melioidosis without the spread to the bloodstream, chest X-ray most commonly shows upper lobe consolidation or cavitations. In chronic melioidosis, the slow progression of upper lobe consolidation of the lungs resembles tuberculosis.
For abscesses located in other parts of the body apart from the lungs, especially in the liver and spleen, CT scan has higher sensitivity when compared with an ultrasound scan. In liver and splenic abscesses, an ultrasound scan shows “target-like” lesions while a CT scan shows “honeycomb sign” (abscess with loculations separated by thin septa) in liver abscesses.
For melioidosis involving the brain, MRI has higher sensitivity than a CT scan in diagnosing the lesion. MRI shows ring-enhancing lesions for brain melioidosis
Prevention
Bacterial culture has 60% sensitivity in diagnosing melioidosis.
B. pseudomallei is never part of human flora. Therefore, any growth of the bacteria is diagnostic of melioidosis.
Other samples such as throat, rectal swabs, pus from abscesses, and sputum can also be used for culture. However, culture from CSF is difficult because in one case series, only 29% of the neuromelioidosis cases are culture-positive. When bacteria do not grow from people strongly suspected of having melioidosis, repeated cultures should be taken as subsequent cultures can become positive B. pseudomallei can be grown on any blood agar, MacConkey agar, and agar containing antibiotics such as Ashdown’s medium (containing gentamicin)nand Ashdown’s broth (containing colistin for better isolation of B. pseudomallei from other types of bacteria. Agar plates for melioidosis should be incubated at 37 °C (98.6 °F) in air and inspected daily for four days. On the agar plates, B. pseudomallei forms creamy, non-haemolytic, colonies after 2 days of incubation. After 4 days of incubation, colonies appear dry and wrinkled. Colonies ofB. pseudomallei that are grown on Franci’s medium (a modification of Ashdown medium with gentamicin concentration increased to 8 mg/L and neutral red indicator replaced with 0.2% bromocresol purple) are yellowed to symptom overlap with TB and other infections.
Treatment:
Intensive phase: IV antibiotics (e.g., ceftazidime or meropenem) for 2–8 weeks
Eradication phase: Oral antibiotics (e.g., trimethoprim-sulfamethoxazole) for 3–6 months to prevent relapseDelayed diagnosis and treatment can lead to mortality rates as high as 90% in severe cases. doves.
Treatment of melioidosis can be difficult, as B. pseudomallei is often resistant to multiple antibiotics, and a prolonged course of antibiotics is required to prevent disease relapse. Due to the severity of melioidosis and aerosol transmissibility of the infectious agent, B. pseudomallei has been classified as a category B bioterrorism and Tier 1 select agent by the Center for Disease Control, USA.
Prevention – Efforts to prevent melioidosis include: wearing protective gear while handling contaminated water or soil, practicing hand hygiene, drinking boiled water, and avoiding direct contact with soil, water, or heavy rain.
There is little evidence to support the use of melioidosis prophylaxis in humans.
The antibiotic co-trimoxazole is used as a preventative only for individuals at high risk of getting the disease after being exposed to the bacteria in laboratory settings.
Public Health Implications. Melioidosis is increasingly recognized as a neglected tropical disease.
Its burden is underestimated, especially in resource-limited settings.
Climate change, extreme weather events, and expanding endemic zones (including parts of India) are raising global concern.
Vaccine Development Breakthroughs.
Researchers are actively pursuing vaccines to combat melioidosis,
with several promising candidates emerging: Over the years, numerous different strategies have been explored to develop melioidosis vaccines. Based on the choice of protective antigens, many of the resulting candidates would also be predicted to provide some level of protection against Burkholderia mallei, the etiologic agent of glanders. Using these approaches, several promising melioidosis and glanders candidates have been identified with pre-clinical animal studies providing valuable insights into the immunogenic and protective capacities of these potential vaccines. Collectively, this review summarizes recent advancements in melioidosis vaccine research and highlights critical findings that will help guide a path toward the development of a safe, effective and affordable vaccine to combat disease caused by B. pseudomallei.- Subunit vaccinesusing protective antigens from B. pseudomallei have shown strong immunogenicity in preclinical modelsYet there are no vaccines available for humans
Hand and Skin Hygiene.
Wash hands thoroughly with soap and clean water after handling soil or water in affected areas, particularly before eating or drinking.
