Melioidosis in Vietnam: Recently Improved Recognition but still an Uncertain Disease Burden after Almost a Century of Reporting

Clinical presentation and treatment of 2 patients with infection caused by Chromobacterium violaceum in Vietnam

Chromobacterium violaceum is a rare but severe and often fatal cause of disease in humans. We present 2 clinical cases of sepsis and skin abscesses / cellulitis caused by C. violaceum seen in a referral hospital for infectious diseases in Vietnam. Both patients survived, but appropriate antibiotic treatment was only installed after culture of the organism. We reviewed and summarised the characteristics of C. violaceum infection and treatment.

Newly detected paediatric melioidosis cases in a single referral children's hospital in Ho Chi Minh City indicate the probable underrecognition of melioidosis in South Vietnam

BACKGROUND

The epidemiology of melioidosis in Vietnam, a disease caused by the soil bacterium Burkholderia pseudomallei, remains unclear. This study aimed to detect paediatric melioidosis in South Vietnam and describe clinical features and the geographic distribution.

METHODS

We introduced a simple laboratory algorithm for detecting B. pseudomallei from clinical samples at Children's Hospital 2 in Ho Chi Minh City in July 2015. A retrospective observational study of children <16 y of age with culture-confirmed melioidosis between July 2015 and August 2019 was undertaken.

RESULTS

Thirty-five paediatric cases of melioidosis were detected, with cases originating from 13 of 32 provinces and cities in South Vietnam. The number of paediatric melioidosis cases detected from a certain region correlated with the overall number of inpatients originating from the respective geographic area. Suppurative parotitis (n=15 [42.8%]) was the most common clinical presentation, followed by lung infection (n=10 [28.6%]) and septicaemia (n=7 [20%]). Fourteen (40%) children had disseminated disease, including all cases of lung infection, four cases with central nervous system symptoms and four (11.4%) deaths.

CONCLUSIONS

The patients' origin indicates a wide distribution of melioidosis in South Vietnam. It seems probable that cases not only in children, but also in adults, remain grossly undiagnosed. Further awareness raising and laboratory capacity strengthening are needed in this part of the country.

A Graphical Overview of the Histopathology of Human Melioidosis: A Case Series

Background

Melioidosis, caused by the Gram-negative bacterium Burkholderia pseudomallei, has a major global health impact and a wide range of different disease manifestations. Histopathological descriptions of melioidosis remain limited. Granulomatous inflammation with multinucleated giant cells are considered classic features. We aim to present a graphical overview of histopathological manifestations of melioidosis, serving as an aid in diagnosing this disease.

Methods

We performed a retrospective international multicenter laboratory-based analysis of formalin-fixed paraffin-embedded (FFPE) tissue from culture-confirmed melioidosis autopsy and biopsy cases. Available FFPE tissue was stained with hematoxylin and eosin and immunostainings including a monoclonal antibody targeting the capsular polysaccharide (CPS) of B pseudomallei. Tissue with site-specific cultures and/or positive CPS staining were included in the graphical histopathological overview.

Results

We identified tissue of 8 autopsy and 5 biopsy cases. Pneumonia and soft tissue abscesses were the leading foci of disease displaying mainly necrosis and suppuration. Infrequent disease manifestations included involvement of bone marrow and adrenal glands in an autopsy case and biopsied mediastinal tissue, the latter being the only case in which we identified multinucleated giant cells. Using the CPS staining, we demonstrated granulomata as part of rare gastric tissue involvement.

Conclusions

We found fatal melioidosis to be a necrotizing and suppurative inflammation, usually without multinucleated giant cell formation. Gastric and mediastinal involvement points to ingestion and inhalation as possible routes of infection. The CPS staining proved beneficial as an aid to establish a histopathological diagnosis. Our graphical overview can be used by infectious diseases specialists, microbiologists, and pathologists.

Hcp1-loaded staphylococcal membrane vesicle vaccine protects against acute melioidosis

Burkholderia pseudomallei is the causal agent of melioidosis, a deadly tropical infectious disease that lacks a vaccine. On the basis of the attenuated Staphylococcus aureus RN4220-Δagr (RN), we engineered the RN4220-Δagr/pdhB-hcp1 strain (RN-Hcp1) to generate B. pseudomallei hemolysin-coregulated protein 1 (Hcp1)-loaded membrane vesicles (^hcp1MVs). The immunization of BALB/c mice with ^hcp1MVs mixed with adjuvant by a three-dose regimen increased the serum specific IgG production. The serum levels of inflammatory factors, including TNF-α and IL-6, in ^hcp1MV-vaccinated mice were comparable with those in PBS-challenged mice. The partial adjuvant effect of staphylococcal MVs was observed with the elevation of specific antibody titer in ^hcp1MV-vaccinated mice relative to those that received the recombinant Hcp1 protein (rHcp1) or MVs derived from RN strain (^ΔagrMVs). The ^hcp1MVs/adjuvant vaccine protected 70% of mice from lethal B. pseudomallei challenge. Immunization with ^hcp1MVs only protected 60% of mice, whereas vaccination with rHcp1 or ^ΔagrMVs conferred no protection. Moreover, mice that received ^hcp1MVs/adjuvant and ^hcp1MVs immunization had low serum TNF-α and IL-6 levels and no inflammatory infiltration in comparison with other groups. In addition, all surviving mice in ^hcp1MVs/adjuvant and ^hcp1MVs groups exhibited no culturable bacteria in their lungs, livers, and spleens five days postinfection. Overall, our data highlighted a new strategy for developing B. pseudomallei vaccine and showed that Hcp1-incorporated staphylococcal MV is a promising candidate for the prevention of acute melioidosis.

Burden and Risk Factors of Melioidosis in Southeast Asia: A Scoping Review

This scoping review aims to provide a comprehensive overview of human melioidosis in Southeast Asia as well as to highlight knowledge gaps in the prevalence and risk factors of this life-threatening disease using available evidence-based data for better diagnosis and treatment. Preferred Reporting Items for Systematic Review and Meta-Analyses Extension for Scoping Reviews (PRISMA-ScR) was used as the guideline for this review. The literature search was conducted on 23 March 2022 through two electronic databases (PubMed and Scopus) using lists of keywords referring to the Medical Subject Headings (MeSH) thesaurus. A total of 38 articles related to human melioidosis were included from 645 screened articles. These studies were carried out between 1986 and 2019 in six Southeast Asian countries: Thailand, Cambodia, Malaysia, Myanmar, Singapore, and Vietnam. Melioidosis has been reported with a high disease prevalence among high-risk populations. Studies in Thailand (48.0%) and Cambodia (74.4%) revealed disease prevalence in patients with septic arthritis and children with suppurative parotitis, respectively. Other studies in Thailand (63.5%) and Malaysia (54.4% and 65.7%) showed a high seroprevalence of melioidosis among Tsunami survivors and military personnel, respectively. Additionally, this review documented soil and water exposure, diabetes mellitus, chronic renal failure, thalassemia, and children under the age of 15 as the main risk factors for melioidosis. Human melioidosis is currently under-reported in Southeast Asia and its true prevalence is unknown.

Aetiologies and clinical presentation of central nervous system infections in Vietnamese patients: a prospective study

Knowledge of the clinical presentation of central nervous system (CNS) infections and the causative pathogens is crucial for appropriate diagnosis and rapid initiation of appropriate treatment to prevent severe neurological sequelae. The aim of this study is to understand the aetiology of CNS infections based on the clinical presentation of Vietnamese patients. A prospective hospital-based cohort study was conducted between May 2014 and May 2017. We screened 137 patients with clinically suspected CNS infection for fungal, bacterial and viral pathogens using their cerebrospinal fluid (CSF) and blood cultures. In addition, DNA or RNA extracted from CSF samples were subjected to nucleic acid testing (NAT) with a selective panel of bacterial, viral and fungal pathogens. At least one pathogen could be detected in 41% (n = 56) of the patients. The main pathogens causing CNS infections were Streptococcus suis (n = 16; 12%) and Neisseria meningitidis (n = 9; 7%), followed by Herpes simplex virus 1/2 (n = 4; 3%) and Klebsiella pneumoniae (n = 4; 3%). Other pathogens were only identified in a few cases. Patients with bacterial CNS infections were significantly older, had a worse outcome, a lower Glasgow Coma Scale (GCS), a higher rate of speech impairment and neck stiffness than patients with viral or tuberculous CNS infections. In northern Vietnam, adults are mostly affected by bacterial CNS infections, which have a severe clinical course and worse outcomes compared to viral or tuberculous CNS infections. Clinicians should be aware of the regional occurrence of pathogens to initiate rapid and appropriate diagnosis and treatment.

Child Melioidosis Deaths Caused by Burkholderia pseudomallei-Contaminated Borehole Water, Vietnam, 2019

Within 8 months, 3 children from 1 family in northern Vietnam died from melioidosis. Burkholderia pseudomallei of the same sequence type, 541, was isolated from clinical samples, borehole water, and garden and rice field soil. Boreholes should be properly constructed and maintained to avoid B. pseudomallei contamination.

Thermal and gastric stability of antimicrobial activity of juices and aqueous extracts prepared from common eligible herbs and traditional medicinal plants against Burkholderia pseudomallei and other enteric bacteria

Background

Burkholderia pseudomallei is a causative agent of melioidosis, a fatal infectious disease highly prevalent in the tropics where traditional medicinal plants are widely used for the treatment of various human ailments. In this study, we aimed to evaluate the in vitro antibacterial activity of common eligible herbs and medicinal plants against B. pseudomallei. Thermal and gastric stability, antibacterial spectrum, bactericidal activity, and cell cytotoxicity were also tested to verify the possible usage of these plants in the treatment of melioidosis.

Results

Eighteen eligible herbs and twenty-one medicinal plants were collected. Herb juices and aqueous plant samples extracted at different temperatures were prepared for antibacterial testing. A higher proportion of aqueous plant extracts (17/21; 80.9%) against B. pseudomallei was observed, in comparison with that of herb juices (8/18; 44.5%). Two herb juices and twelve aqueous plant extracts were selected for further tests. The juices of A. sativum and A. tuberosum decreased their antimicrobial activity when treated at higher temperatures whereas the aqueous plant extracts increased their antimicrobial activity when prepared at 70 and 100 °C. The herb juices showed a broader spectrum of antimicrobial activity than the aqueous plant extracts. All samples showed less cytotoxicity on the HT29, HepG2, and HEK293 cell lines. At the 2× minimal inhibitory concentration (MIC), aqueous extracts of Blechnum orientale, Breynia fruticose, Psidium guajava, Rhodomyrtus tomentosa, Rosa odorata, and Schima wallichii showed similar bactericidal activity to that of amoxicillin clavulanic acid. The antimicrobial activity of Mangifera indica, Punica granatum, and R. tomentosa remained under the stimulated gastric conditions.

Conclusion

Our data indicate that traditional medicinal plants prepared by decoction could be effectively used to treat melioidosis via the oral route. Further in vivo investigations are needed to explore other alternative therapies for the prevention and treatment of tested pathogenic bacterial species.

Melioidosis in Africa: Time to Raise Awareness and Build Capacity for Its Detection, Diagnosis, and Treatment

Melioidosis is a tropical infectious disease caused by the soil-dwelling bacterium Burkholderia pseudomallei with a mortality of up to 50% in low resource settings. Only a few cases have been reported from African countries. However, studies on the global burden of melioidosis showed that Africa holds a significant unrecognized disease burden, with Nigeria being at the top of the list. The first World Health Organization African Melioidosis Workshop was organized in Lagos, Nigeria, with representatives of health authorities, microbiology laboratories, and clinical centers from across the continent. Dedicated hands-on training was given on laboratory diagnostics of B. pseudomallei. This report summarises the meeting objectives, including raising awareness of melioidosis and building capacity for the detection, diagnosis, biosafety, treatment, and prevention across Africa. Further, collaboration with regional and international experts provided a platform for sharing ideas on best practices.

Burkholderia pseudomallei triggers canonical inflammasome activation in a human primary macrophage-based infection model

Most of the current knowledge on Burkholderia pseudomallei-induced inflammasome activation and cell death in macrophages is derived from murine systems. Little is known about the involved bacterial structures and mechanisms in primary human macrophages. This is of particular relevance since murine and human macrophages as well as primary cells and cell lines differ in many aspects of inflammasome activation, including the proteins involved in the recognition of bacterial patterns. In this study, we therefore aimed (i) to establish an in vitro B. pseudomallei infection model with human monocyte-derived primary macrophages from single donors as these cells more closely resemble macrophages in the human host and (ii) to analyze B. pseudomallei-triggered cell death and bacterial elimination in those cells. Our results show that B. pseudomallei-infected primary human macrophages not only release the inflammasome-independent pro-inflammatory cytokines IL-8 and TNF-α, but are also engaged in canonical inflammasome activation as evidenced by caspase-1 and gasdermin D processing. Absence of the B. pseudomallei T3SS-3 needle protein BsaL, a potent activator of the canonical inflammasome, abolished lytic cell death, reduced IL-1β release, and caspase-1 and gasdermin D processing. IFN-γ, known to promote non-canonical inflammasome activation, did not influence pyroptosis induction or IL-1β release from infected primary human macrophages. Nevertheless, it reduced intracellular B. pseudomallei loads, an effect which was partially antagonist by the inhibition of NADPH oxidase. Overall, our data implicate T3SS-3 dependent inflammasome activation and IFN-γ induced immune mechanisms as critical defense mechanisms of human macrophages against B. pseudomallei. In addition, our infection model provides a versatile tool to study human host-pathogen interactions and has the potential to elucidate the role of human individual genetic variations in B. pseudomallei infections.

Considering the constantly emerging antibiotic resistance of pathogens, comprehensive analyses of immune response mechanisms against infections are urgently needed to provide the basis for novel therapeutic strategies. Studies based on primary murine cells and cell lines of murine and human origin led to advances in the understanding of immune defense mechanisms against bacterial infections including B. pseudomallei. Nevertheless, results relying on these cell types are not always transferrable to primary human cells due to e.g. pathway alterations. We established and validated a macrophage-based model system derived from human peripheral blood monocytes, which yields high amounts of genetically identical cells more closely resembling cells found in the human host. This model system provides the basis for studying the pathogenesis of B. pseudomallei in primary human macrophages and for developing new human host directed therapies avoiding pitfalls from cell lines. Using our newly established model we demonstrate, that restriction of B. pseudomallei by primary human macrophages is mediated by T3SS-3 dependent canonical inflammasome activation and IFN-γ induced intracellular bacterial restriction.

Distribution of Serological Response to Burkholderia pseudomallei in Swine from Three Provinces of Vietnam

(1) Background: Burkholderia pseudomallei is an environmentally mediated saprophytic pathogen that can cause severe disease in humans. It is well known that B. pseudomallei survives in tropical moist soil environments worldwide, but melioidosis is gaining recognition as a public and veterinary health issue in Vietnam. The contribution of animals to human disease is unknown, necessitating further investigation. (2) Methods: Swine sera were collected from two populations, one grazing and one commercially farmed, from three provinces in Vietnam. ELISAs utilizing B. pseudomallei capsular polysaccharide (CPS), outer polysaccharide (OPS), and Hcp1 protein were used to screen serum samples. Positive samples were mapped to the commune level. Seroprevalence calculations and pig population estimates were used to approximate number of swine exposures per commune. (3) Results: Grazing pigs from Hoa Binh had significantly higher seropositivity levels (11.4%, 95% CI: 9.7–13.1) compared to farmed pigs from Ha Tinh and Nghe An (4%, 95% CI: 3.3–4.7). Average swine seropositivity rates were ~6.3% (95% CI: 5–7.9), higher than previously identified in Vietnam (~0.88%). (4) Conclusions: Initial serological sampling identified a significant number of seropositive and potential melioidosis infections occurring in swine in Vietnam. This work is a critical step in understanding the role swine may play in the epidemiology of human melioidosis in Vietnam.

Melioidosis DS rapid test: A standardized serological dipstick assay with increased sensitivity and reliability due to multiplex detection

BACKGROUND

Melioidosis, caused by Burkholderia pseudomallei, is a severe infectious disease with high mortality rates, but is under-recognized worldwide. In endemic areas, there is a great need for simple, low-cost and rapid diagnostic tools. In a previous study we showed, that a protein multiplex array with 20 B. pseudomallei-specific antigens detects antibodies in melioidosis patients with high sensitivity and specificity. In a subsequent study the high potential of anti-B. pseudomallei antibody detection was confirmed using a rapid Hcp1 single protein-based assay. Our protein array also showed that the antibody profile varies between patients, possibly due to a combination of host factors but also antigen variations in the infecting B. pseudomallei strains. The aim of this study was to develop a rapid test, combining Hcp1 and the best performing antigens BPSL2096, BPSL2697 and BPSS0477 from our previous study, to take advantage of simultaneous antibody detection.

METHODS AND PRINCIPAL FINDINGS

The 4-plex dipstick was validated with sera from 75 patients on admission plus control groups, achieving 92% sensitivity and 97-100% specificity. We then re-evaluated melioidosis sera with the 4-plex assay that were previously misclassified by the monoplex Hcp1 rapid test. 12 out of 55 (21.8%) false-negative samples were positive in our new dipstick assay. Among those, 4 sera (7.3%) were Hcp1 positive, whereas 8 (14.5%) sera remained Hcp1 negative but gave a positive reaction with our additional antigens.

CONCLUSIONS

Our dipstick rapid test represents an inexpensive, standardized and simple diagnostic tool with an improved serodiagnostic performance due to multiplex detection. Each additional band on the test strip makes a false-positive result more unlikely, contributing to its reliability. Future prospective studies will seek to validate the gain in sensitivity and specificity of our multiplex rapid test approach in different melioidosis patient cohorts.

Burkholderia pseudomallei Detection among Hospitalized Patients, Sarawak

Burkholderia pseudomallei infections are prevalent in Southeast Asia and northern Australia and often misdiagnosed. Diagnostics are often neither sensitive nor rapid, contributing up to 50% mortality rate. In this 2018 pilot study, we enrolled 100 patients aged 6 months-79 years from Kapit Hospital in Sarawak, Malaysia, with symptoms of B. pseudomallei infection. We used three different methods for the detection of B. pseudomallei: a real-time polymerase chain reaction (PCR) assay, a rapid lateral flow immunoassay, and the standard-of-care bacterial culture-the gold standard. Among the 100 participants, 24 (24%) were positive for B. pseudomallei by one or more of the detection methods. Comparing the two individual diagnostic methods against the gold standard-bacterial culture-of any positive test, there was low sensitivity for each test (25-44%) but high specificity (93-98%). It seems clear that more sensitive diagnostics or a sensitive screening diagnostic followed by specific confirmatory diagnostic is needed for this disease.

Human Melioidosis

The causative agent of melioidosis, Burkholderia pseudomallei, a tier 1 select agent, is endemic in Southeast Asia and northern Australia, with increased incidence associated with high levels of rainfall. Increasing reports of this condition have occurred worldwide, with estimates of up to 165,000 cases and 89,000 deaths per year. The ecological niche of the organism has yet to be clearly defined, although the organism is associated with soil and water. The culture of appropriate clinical material remains the mainstay of laboratory diagnosis. Identification is best done by phenotypic methods, although mass spectrometric methods have been described. Serology has a limited diagnostic role. Direct molecular and antigen detection methods have limited availability and sensitivity. Clinical presentations of melioidosis range from acute bacteremic pneumonia to disseminated visceral abscesses and localized infections. Transmission is by direct inoculation, inhalation, or ingestion. Risk factors for melioidosis include male sex, diabetes mellitus, alcohol abuse, and immunosuppression. The organism is well adapted to intracellular survival, with numerous virulence mechanisms. Immunity likely requires innate and adaptive responses. The principles of management of this condition are drainage and debridement of infected material and appropriate antimicrobial therapy. Global mortality rates vary between 9% and 70%. Research into vaccine development is ongoing.

Erythritol as a single carbon source improves cultural isolation of Burkholderia pseudomallei from rice paddy soils

BACKGROUND

Isolation of the soil bacterium Burkholderia pseudomallei from tropical environments is important to generate a global risk map for man and animals to acquire the infectious disease melioidosis. There is increasing evidence, that the currently recommended soil culture protocol using threonine-basal salt solution with colistin (TBSS-C50) for enrichment of B. pseudomallei and Ashdown agar for subsequent subculture lacks sensitivity. We therefore investigated, if the otherwise rarely encountered erythritol catabolism of B. pseudomallei might be exploited to improve isolation of this bacterium from soil.

METHODOLOGY/PRINCIPAL FINDINGS

Based on TBSS-C50, we designed a new colistin-containing medium with erythritol as the single carbon source (EM). This medium was validated in various culture protocols by analyzing 80 soil samples from 16 different rice fields in Vietnam. B. pseudomallei enrichment was determined in all culture supernatants by a specific quantitative PCR (qPCR) targeting the type three secretion system 1. 51 out of 80 (63.8%) soil samples gave a positive qPCR signal in at least one of the culture conditions. We observed a significantly higher enrichment shown by lower median cycle threshold values for B. pseudomallei in a two-step culture with TBSS-C50 for 48 h followed by EM for 96h compared to single cultures in TBSS-C50 for either 48h or 144h (p<0.0001, respectively). Accordingly, B. pseudomallei could be isolated on Ashdown agar in 58.8% (30/51) of samples after subcultures from our novel two-step enrichment culture compared to only 9.8% (5/51) after standard enrichment with TBSS-C50 for 48h (p<0.0001) or 25.5% (13/51; p<0.01) after TBSS-C50 for 144h.

CONCLUSIONS/SIGNIFICANCE

In the present study, we show that specific exploitation of B. pseudomallei metabolic capabilities in enrichment protocols leads to a significantly improved isolation rate of this pathogen from soil compared to established standard procedures. Our new culture method might help to facilitate the creation of environmental risk maps for melioidosis in the future.

Endemic Melioidosis in Southern China: Past and Present

Melioidosis is a severe tropical infectious disease caused by the soil-dwelling bacterium Burkholderia pseudomallei, predominantly endemic to Southeast Asia and northern Australia. Between the 1970s and the 1990s, the presence of B. pseudomallei causing melioidosis in humans and other animals was demonstrated in four coastal provinces in southern China: Hainan, Guangdong, Guangxi, and Fujian, although indigenous cases were rare and the disease failed to raise concern amongst local and national health authorities. In recent years, there has been a rise in the number of melioidosis cases witnessed in the region, particularly in Hainan. Meanwhile, although China has established and maintained an effective communicable disease surveillance system, it has not yet been utilized for melioidosis. Thus, the overall incidence, social burden and epidemiological features of the disease in China remain unclear. In this context, we present a comprehensive overview of both historical and current information on melioidosis in Southern China, highlighting the re-emergence of the disease in Hainan. Surveillance and management strategies for melioidosis should be promoted in mainland China, and more research should be conducted to provide further insights into the present situation.