• Epidemiology is the research into how illnesses impact people’s health and the illness of populations. Burkholderia pseudomallei is a type of bacteria that can cause melioidosis, a severe infection affecting various body parts. The epidemiology of Burkholderia pseudomallei is essential to comprehend the potential for environmental exposure to this virus and to prevent its spread.
• The web search results show that some of the main points about the epidemiology of Burkholderia pseudomallei are:
• Burkholderia pseudomallei is an environmental bacterium that lives in soil and water, especially in tropical and subtropical regions. It can endure challenging circumstances like high temperatures, pH changes, and nutrient deprivation.
• Melioidosis is endemic in many countries in Southeast Asia, northern Australia, South Asia, China, and some parts of Africa and South America. The highest incidence rates are reported in northeastern Thailand and northern Australia, where melioidosis is a significant cause of sepsis and death.
• Melioidosis can be acquired by direct contact with contaminated soil or water, ingestion, inhalation, or injection through skin abrasions or wounds. The risk factors for exposure include occupational or recreational activities that involve contact with soil or water, such as farming, gardening, construction, mining, fishing, and swimming. Other risk factors include diabetes mellitus, chronic kidney disease, chronic lung disease, alcoholism, and immunosuppression.
• The clinical manifestations of melioidosis vary widely depending on the infection route, the bacteria dose, and the host immune response. Melioidosis can present as an acute or chronic infection, with symptoms ranging from mild skin ulcers or abscesses to severe pneumonia, septicemia, osteomyelitis, or meningitis. The mortality rate of melioidosis is high, especially in cases of septic shock or disseminated disease.
• According to a retrospective cohort study in Singapore from 2003 to 2014, the overall prevalence rate of melioidosis was 4.65 cases per 100,000 population per year. The annual decline in the overall death rate, 18.4%, was 12.3%. Annual B. pseudomallei bacteremia cases among melioidosis patients had a marginally decreasing trend (absolute risk reduction of 1.1%).
• According to a review and revision of the Darwin melioidosis treatment guideline in Australia from 2012 to 2017, the overall mortality rate of melioidosis was 6.8%. The recrudescence rate (reappearance of symptoms after initial improvement) was 2.8%, and the recurrence rate (relapse or new infection after completion of therapy) was 4.7%. Recrudescence and relapse were mostly caused by osteomyelitis that required surgery and continued to do so.

• Kingdom: Bacteria
• Phylum: Proteobacteria
• Class: Betaproteobacteria
• Order: Burkholderiales
• Family: Burkholderiaceae
• Genus: Burkholderia
• Species: Burkholderia pseudomallei
• Cell Wall Composition: Burkholderia pseudomallei possesses a Gram-negative A cell wall’s outer membrane makes up the cell wall, a peptidoglycan layer, and an inner membrane. The outer membrane contains lipopolysaccharides (LPS) that contribute to its virulence and interaction with the host immune system.
• Flagella: The bacterium is motile due to the presence of multiple flagella. These whip-like structures extend from the cell surface, enabling the bacterium to move in liquid environments. It may facilitate its spread within the host’s body or environment.
• Capsule: Burkholderia pseudomallei is known to produce a capsular polysaccharide layer that surrounds the bacterial cell. This capsule helps the bacterium evade host immune responses, making it more difficult for immune cells to recognize and eliminate the pathogen.
• Pili: Pili, also known as fimbriae, are hair-like appendages on the bacterial surface that play a role in adhesion to host cells and surfaces. Burkholderia pseudomallei pili are involved in initial attachment to host cells and can contribute to establishing infection.
• Intracellular Survival: Burkholderia pseudomallei can survive and replicate within host cells, such as macrophages. Its ability to invade and persist within these cells is critical to the bacterium’s ability to cause chronic and recurring infections in the host.

• Four antigenic types of  Burkholderia pseudomallei are based on the lipopolysaccharide (LPS) O-antigen, a component of the bacterial outer membrane and a virulence factor. The four types are:
• Type A: This is the most common type and has a typical LPS ladder pattern on SDS-PAGE. It is highly prevalent in strains from Thailand and other countries in Southeast Asia.
• Type B: This is an atypical type with a different LPS ladder pattern on SDS-PAGE. It is most often detected in Australian strains (about 13.8%).
• Type B2: This novel type has a derivative of the atypical LPS ladder pattern on SDS-PAGE. It is associated with an uncommon O-antigen biosynthesis gene cluster found in only a small subpopulation of B. pseudomallei.
• Rough type: This type lacks the repeating unit of the O-antigen and has no visible LPS ladder pattern on SDS-PAGE. Natural mutations in the O-antigen biosynthesis genes cause it.
• LPS diversity may be correlated with varying immunopathogenicity & virulence among various species B. pseudomallei strains.
• The O-antigen types also show some sero-crossreactivity with other Burkholderia species, which may complicate the diagnosis and vaccine development for melioidosis.

Pathogenesis is the process by which a microorganism causes disease in a host. Melioidosis is a severe infection involving numerous body regions that can be brought on by a kind of bacteria called Burkholderia pseudomallei. The pathogenesis of Burkholderia pseudomallei involves several steps, such as:

• Transmission: Burkholderia pseudomallei is an environmental bacterium that lives in soil and water, especially in tropical and subtropical regions. It can infect humans and animals through direct contact with contaminated sources, such as inhalation, ingestion, or injection through skin abrasions or wounds.
• Attachment: Burkholderia pseudomallei can attach to the epithelial cells of the lungs or skin, possibly using bacterial components such as the capsule and type IV pili. The capsule is a polysaccharide layer that protects the bacteria from phagocytosis and complement-mediated killing. The Type IV pili are hair-like structures that mediate adhesion, motility, and biofilm formation.
• Invasion: Burkholderia pseudomallei can invade the host cells by inducing its uptake through actin rearrangement or by exploiting the endocytic pathways of the cells. The bacteria can also escape from the endosomes into the cytoplasm by secreting enzymes that degrade the endosomal membrane.
• Survival: Burkholderia pseudomallei can survive and replicate within the host cells by evading or modulating the host immune response. The bacteria can use several mechanisms, such as:
• Type III secretion system (T3SS): This needle-like apparatus injects bacterial proteins into the host cells. These proteins can interfere with cellular functions, such as signal transduction, cytoskeleton dynamics, apoptosis, and inflammation.
• Toxins: These molecules can damage or kill the host cells or tissues. Some examples of toxins Burkholderia pseudomallei produce are BPSL1549, BPSL1629, and BPSL1631.
• Enzymes: These molecules can catalyze biochemical reactions and modify the host environment. Some examples of enzymes Burkholderia pseudomallei produces are Catalase, Superoxide dismutase, and Penicillin-binding proteins.
• Dissemination: Burkholderia pseudomallei can spread from the primary infection source to nearby organs or tissues using actin-based motility or forming biofilms on abiotic surfaces or within blood vessels. The bacteria can also form dormant forms called persister cells that can survive antibiotic treatment and reactivate later to cause relapse or chronic infection.

• Host defenses are the mechanisms by which the host organism protects itself from pathogens, such as bacteria, viruses, fungi, and parasites. Burkholderia pseudomallei is a type of bacteria that can cause melioidosis, a severe infection affecting various body parts. The host defenses of Burkholderia pseudomallei involve innate and adaptive immunity, the two main branches of the immune system.

Innate Immunity:

• Phagocytosis: The immune cells, such as macrophages and neutrophils, attempt to engulf and destroy Burkholderia pseudomallei. The bacterium can resist phagocytosis by producing a capsule that prevents opsonization and secreting enzymes that degrade the phagosome membrane.
• Extracellular Traps: Neutrophils or macrophages release extracellular traps to capture and kill bacteria. Burkholderia pseudomallei can evade these traps by producing nucleases or expressing type IV pili for motility and detachment.
• Inflammasome Activation: The bacterium can activate the inflammasome through various mechanisms, but it can also modulate this activation using structural variations or secreting effectors that interfere with signaling pathways.

Adaptive Immunity:

• T Cell-Mediated Immunity: T cells, particularly CD8+ cytotoxic T cells and CD4+ T helper cells, are crucial in targeting intracellular bacteria like Burkholderia pseudomallei. CD4+ T cells activate macrophages and enhance B cell antibody production, while CD8+ T cells directly kill infected cells.
• Antibody-Mediated Immunity: B cells produce antibodies that bind to antigens on the bacterium’s surface, neutralizing or marking it for destruction by phagocytes or complement proteins. Antibodies can also trigger antibody-dependent cellular cytotoxicity (ADCC), leading to the destruction of bacteria by natural killer cells.

• Burkholderia pseudomallei is a type of bacteria that can cause a severe melioidosis infection. This infection can affect various body parts, such as the skin, lungs, bones, joints, and brain. The clinical manifestations of Burkholderia pseudomallei depend on how the bacteria enter the body and how severe the infection is. Several warning signs and symptoms include:
• Sweating, chills, and fever
• Headache, sore throat, and cough
• Shortness of breath and chest pain
• Abdominal pain and diarrhea
• joint discomfort and aching muscles
• Skin ulcers, abscesses, or nodules
• Confusion, seizures, or coma
• Melioidosis can be a life-threatening condition that requires prompt diagnosis and treatment. The diagnosis is usually confirmed by growing the bacteria from a sample of blood, sputum, urine, or pus. The treatment involves many antibiotics, sometimes combined with surgery to drain, or remove infected tissue.

• The isolation and identification of Burkholderia pseudomallei is difficult because of the limited sensitivity of culture methods, the phenotypic similarity of Burkholderia pseudomallei to other Burkholderia species, and the need for more awareness and laboratory capacity.
• Some of the laboratory methods that can be used to diagnose Burkholderia pseudomallei are:
• Culture: This traditional method involves growing Burkholderia pseudomallei on culture media, such as blood agar, MacConkey agar, or Ashdown’s agar. The characteristic cornflower head morphology of colonies helps identify the bacterium. Biochemical tests further confirm its identity, including oxidase, catalase, nitrate reduction, and arabinose assimilation. Culture can take 2 to 7 days and is reliable but time-consuming.
• Molecular Methods: These modern techniques detect the genetic material of Burkholderia pseudomallei. Polymerase chain reaction (PCR) amplifies specific DNA segments for identification. The MALDI-TOF MS, or matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, is used for rapid identification by comparing the protein profiles of the bacterium. These methods are faster, more sensitive, and more specific than culture.
• Antigen Detection: This method detects Burkholderia pseudomallei antigens using immunological assays like enzyme-linked immunosorbent assay (ELISA) or latex agglutination test (LAT). Specific antibodies bind to the antigens, providing a quick diagnosis. However, this approach may have limitations in endemic areas due to availability and potential cross-reactivity.
• Serology: Serological methods identify antibodies produced in response to Burkholderia pseudomallei infection using assays like indirect hemagglutination assay (IHA), indirect immunofluorescence assay (IFA), or ELISA. These tests measure antibody levels in the serum, offering a supportive diagnosis. However, cross-reactivity with other bacteria or previous exposure to related species can affect sensitivity and specificity, particularly in endemic regions.

The controls and precautions for working with Burkholderia pseudomallei include:

• Laboratory Biosafety Level (BSL): Burkholderia pseudomallei is classified as a BSL-3 pathogen, requiring containment facilities with enhanced precautions to prevent accidental exposure. Researchers and laboratory staff must be trained and follow strict protocols when working with this bacterium.
• Personal Protective Equipment (PPE): Individuals working with Burkholderia pseudomallei must wear appropriate PPE, including gloves, laboratory coats, eye protection (safety goggles or face shields), and respiratory protection (N95 masks or higher).
• Engineering Controls: Laboratories working with Burkholderia pseudomallei must have proper engineering controls in place, such as biological safety cabinets (BSCs) or other containment equipment, to prevent the release of the bacterium into the environment.
• Access Restrictions: Access to the laboratory should only be restricted to authorized personnel. Entry and exit procedures must be followed to minimize the risk of contamination.
• Decontamination: Surfaces and equipment that meet Burkholderia pseudomallei must be regularly decontaminated using appropriate disinfectants.

Melioidosis: Epidemiology, clinical manifestations, and diagnosis – UpToDate

Decoding Burkholderia Pseudomallei for the Laboratory | NETEC