The epidemiology of melioidosis in the Balimo region of Papua New Guinea

Tropical fever in remote tropics: tuberculosis or melioidosis, it depends on the lab

Diagnostics tests used to identify the cause of infection using proteomics and genomics have revolutionised microbiology laboratories in recent times. However, approaches to build the capacity of clinical microbiology services in the rural tropics by simply transplanting these approaches have proven difficult to sustain. Tropical fever in the remote tropics is, by definition, a clinical diagnosis where the aetiology of fever is not known, treatment is empirical, guided by clinical suspicion with treatment failure often attributed to incorrect diagnosis or antimicrobial resistance. Tuberculosis (TB) in rural Papua New Guinea (PNG) is mostly diagnosed clinically, perhaps supported by microscopy. In fact, a ‘tuberculosis patient’ in rural PNG is included in the TB register upon commencement of TB treatment with or without any laboratory-based evidence of infection. The roll-out of GeneXpert is continuing to transform TB diagnostic certainty in TB endemic communities. Melioidosis is endemic in tropical regions and is increasingly reported to mimic TB. Isolation and identification of the causative agent Burkholderia pseudomallei remains the gold standard. Here, we discuss the increasing divide between rural and urban approaches to laboratory-based infection diagnosis using these two enigmatic tropical infectious diseases, in rural PNG, as examples.

Burkholderia pseudomallei pathogenesis and survival in different niches

Burkholderia pseudomallei (Bp) is the causative agent of melioidosis, a disease of the tropics with high clinical mortality rates. To date, no vaccines are approved for melioidosis and current treatment relies on antibiotics. Conversely, common misdiagnosis and high pathogenicity of Bp hamper efforts to fight melioidosis. This bacterium can be isolated from a wide range of niches such as waterlogged fields, stagnant water bodies, salt water bodies and from human and animal clinical specimens. Although extensive studies have been undertaken to elucidate pathogenesis mechanisms of Bp, little is known about how a harmless soil bacterium adapts to different environmental conditions, in particular, the shift to a human host to become a highly virulent pathogen. The bacterium has a large genome encoding an armory of factors that assist the pathogen in surviving under stressful conditions and assuming its role as a deadly intracellular pathogen. This review presents an overview of what is currently known about how the pathogen adapts to different environments. With in-depth understanding of Bp adaptation and survival, more effective therapies for melioidosis can be developed by targeting related genes or proteins that play a major role in the bacteria's survival.

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.

Prevalence and genetic diversity of Burkholderia pseudomallei isolates in the environment near a patient's residence in Northeast Thailand

BACKGROUND

Burkholderia pseudomallei is the causative agent of melioidosis, a severe infectious disease in tropical regions. It is necessary to understand the risk of acquiring this infection from the environment.

METHODOLOGY /PRINCIPAL FINDINGS

The prevalence, concentration and genetic diversity of B. pseudomallei isolates collected from two sites in Buriram, Northeast Thailand were investigated. Forty-four environmental samples (18 from soil, 14 from rice rhizosphere, and 12 from water) were collected; of those 44 samples, 19 were collected from near a patient's residence and 25 from suspected exposure sites and compared with 10 clinical isolates of the patient. Quantitative culture was performed, and B. pseudomallei was identified using the latex agglutination test and matrix-laser absorption ionisation mass spectrometry. Genotyping was performed in 162 colonies from clinical (N = 10) and environmental samples (N = 152) using pulse-field gel electrophoresis (PFGE) followed by multi-locus sequence typing (MLST) of the clinical strain. B. pseudomallei was detected in 11 of the 44 environmental samples (1 from soil, 4 from rice rhizosphere, and 6 from water). The bacterial count in the positive soil sample was 115 CFU/g. The mean concentrations ± SDs of B. pseudomallei in the positive water and rhizosphere samples were 5.1 ± 5.5 CFU/ml and 80 ± 49 CFU/g, respectively. Six water samples with positive results were collected from a pond and water sources for drinking and daily use. All colonies isolated from the patient shared the same PFGE type (PT) indicating monoclonal infection of ST99. Although the 152 colonies from environmental isolates exhibited 25 PTs, none were identical to the patient's isolates. PT5 and PT7 were most common genotype among the environmental samples.

CONCLUSIONS/SIGNIFICANCE

Diverse genotypes of B. pseudomallei were prevalent in the environment. However, the patient may have been infected with a low-density genotype. Intervention strategies for preventing B. pseudomallei infection are required.

Burkholderia pseudomallei distribution in Australasia is linked to paleogeographic and anthropogenic history

Burkholderia pseudomallei is the environmental bacillus that causes melioidosis; a disease clinically significant in Australia and Southeast Asia but emerging in tropical and sub-tropical regions around the globe. Previous studies have placed the ancestral population of the organism in Australia with a single lineage disseminated to Southeast Asia. We have previously characterized B. pseudomallei isolates from New Guinea and the Torres Strait archipelago; remote regions that share paleogeographic ties with Australia. These studies identified regional biogeographical boundaries. In this study, we utilize whole-genome sequencing to reconstruct ancient evolutionary relationships and ascertain correlations between paleogeography and present-day distribution of this bacterium in Australasia. Our results indicate that B. pseudomallei from New Guinea fall into a single clade within the Australian population. Furthermore, clades from New Guinea are region-specific; an observation possibly linked to limited recent anthropogenic influence in comparison to mainland Australia and Southeast Asia. Isolates from the Torres Strait archipelago were distinct yet scattered among those from mainland Australia. These results provide evidence that the New Guinean and Torres Strait lineages may be remnants of an ancient portion of the Australian population. Rising sea levels isolated New Guinea and the Torres Strait Islands from each other and the Australian mainland, and may have allowed long-term isolated evolution of these lineages, providing support for a theory of microbial biogeography congruent with that of macro flora and fauna. Moreover, these findings indicate that contemporary microbial biogeography theories should consider recent and ongoing impacts of globalisation and human activity.

Rivers as carriers and potential sentinels for Burkholderia pseudomallei in Laos

Burkholderia pseudomallei, causative agent of the often fatal disease melioidosis, dwells in tropical soils and has been found in freshwater bodies. To investigate whether rivers are potential habitats or carriers for B. pseudomallei and to assess its geographical distribution in Laos, we studied 23 rivers including the Mekong, applying culture-based detection methods and PCR to water filters and streambed sediments. B. pseudomallei was present in 9% of the rivers in the dry season and in 57% in the rainy season. We found the pathogen exclusively in Southern and Central Laos, and mainly in turbid river water, while sediments were positive in 35% of the B. pseudomallei-positive sites. Our results provide evidence for a heterogeneous temporal and spatial distribution of B. pseudomallei in rivers in Laos with a clear north-south contrast. The seasonal dynamics and predominant occurrence of B. pseudomallei in particle-rich water suggest that this pathogen is washed out with eroded soil during periods of heavy rainfall and transported by rivers, while river sediments do not seem to be permanent habitats for B. pseudomallei. Rivers may thus be useful to assess the distribution and aquatic dispersal of B. pseudomallei and other environmental pathogens in their catchment area and beyond.

Melioidosis in Papua New Guinea and Oceania

Melioidosis has only been sporadically reported throughout Melanesia and the Pacific region since the first report from Guam in 1946; therefore, its contribution to the disease burden in this region is largely unknown. However, the outcome of a small number of active surveillance programs, serological surveys, and presumptive imported cases identified elsewhere provide an insight into its epidemiology and potential significance throughout the region. Both clinical cases and environmental reservoirs have been described from the rural district of Balimo in the Western Province of Papua New Guinea and from the Northern Province of New Caledonia. In both these locations the incidence of disease is similar to that described in tropical Australia and Burkholderia pseudomallei isolates are also phylogenetically linked to Australian isolates. Serological evidence and presumptive imported cases identified elsewhere suggest that melioidosis exists in other countries throughout the Pacific. However, the lack of laboratory facilities and clinical awareness, and the burden of other infections of public health importance such as tuberculosis, contribute to the under-recognition of melioidosis in this region.

Presence of B. thailandensis and B. thailandensis expressing B. pseudomallei-like capsular polysaccharide in Thailand, and their associations with serological response to B. pseudomallei

BACKGROUND

Burkholderia pseudomallei is an environmental Gram-negative bacillus and the cause of melioidosis. B. thailandensis, some strains of which express a B. pseudomallei-like capsular polysaccharide (BTCV), is also commonly found in the environment in Southeast Asia but is considered non-pathogenic. The aim of the study was to determine the distribution of B. thailandensis and its capsular variant in Thailand and investigate whether its presence is associated with a serological response to B. pseudomallei.

METHODOLOGY/PRINCIPAL FINDINGS

We evaluated the presence of B. pseudomallei and B. thailandensis in 61 rice fields in Northeast (n = 21), East (n = 19) and Central (n = 21) Thailand. We found BTCV in rice fields in East and Central but not Northeast Thailand. Fourteen fields were culture positive for B. pseudomallei alone, 8 for B. thailandensis alone, 11 for both B. pseudomallei and B. thailandensis, 6 for both B. thailandensis and BTCV, and 5 for B. pseudomallei, B. thailandensis and BTCV. Serological testing using the indirect hemagglutination assay (IHA) of 96 farmers who worked in the study fields demonstrated that farmers who worked in B. pseudomallei-positive fields had higher IHA titers than those who worked in B. pseudomallei-negative fields (median 1:40 [range: <1:10-1:640] vs. <1:10 [range: <1:10-1:320], p = 0.002). In a multivariable ordered logistic regression model, IHA titers were significantly associated with the presence of B. pseudomallei (aOR = 3.7; 95% CI 1.8-7.8, p = 0.001) but were not associated with presence of B. thailandensis (p = 0.32) or BTCV (p = 0.32). One sequence type (696) was identified for the 27 BTCV isolates tested.

CONCLUSIONS/SIGNIFICANCE

This is the first report of BTCV in Thailand. The presence of B. pseudomallei and B. thailandensis in the same field was not uncommon. Our findings suggest that IHA positivity of healthy rice farmers in Thailand is associated with the presence of B. pseudomallei in rice fields rather than B. thailandensis or BTCV.

Phylogeographic, genomic, and meropenem susceptibility analysis of Burkholderia ubonensis

The bacterium Burkholderia ubonensis is commonly co-isolated from environmental specimens harbouring the melioidosis pathogen, Burkholderia pseudomallei. B. ubonensis has been reported in northern Australia and Thailand but not North America, suggesting similar geographic distribution to B. pseudomallei. Unlike most other Burkholderia cepacia complex (Bcc) species, B. ubonensis is considered non-pathogenic, although its virulence potential has not been tested. Antibiotic resistance in B. ubonensis, particularly towards drugs used to treat the most severe B. pseudomallei infections, has also been poorly characterised. This study examined the population biology of B. ubonensis, and includes the first reported isolates from the Caribbean. Phylogenomic analysis of 264 B. ubonensis genomes identified distinct clades that corresponded with geographic origin, similar to B. pseudomallei. A small proportion (4%) of strains lacked the 920kb chromosome III replicon, with discordance of presence/absence amongst genetically highly related strains, demonstrating that the third chromosome of B. ubonensis, like other Bcc species, probably encodes for a nonessential pC3 megaplasmid. Multilocus sequence typing using the B. pseudomallei scheme revealed that one-third of strains lack the "housekeeping" narK locus. In comparison, all strains could be genotyped using the Bcc scheme. Several strains possessed high-level meropenem resistance (≥32 μg/mL), a concern due to potential transmission of this phenotype to B. pseudomallei. In silico analysis uncovered a high degree of heterogeneity among the lipopolysaccharide O-antigen cluster loci, with at least 35 different variants identified. Finally, we show that Asian B. ubonensis isolate RF23-BP41 is avirulent in the BALB/c mouse model via a subcutaneous route of infection. Our results provide several new insights into the biology of this understudied species.

Pediatric melioidosis in Sarawak, Malaysia: Epidemiological, clinical and microbiological characteristics

Background

Melioidosis is a serious, and potentially fatal community-acquired infection endemic to northern Australia and Southeast Asia, including Sarawak, Malaysia. The disease, caused by the usually intrinsically aminoglycoside-resistant Burkholderia pseudomallei, most commonly affects adults with predisposing risk factors. There are limited data on pediatric melioidosis in Sarawak.

Methods

A part prospective, part retrospective study of children aged <15 years with culture-confirmed melioidosis was conducted in the 3 major public hospitals in Central Sarawak between 2009 and 2014. We examined epidemiological, clinical and microbiological characteristics.

Findings

Forty-two patients were recruited during the 6-year study period. The overall annual incidence was estimated to be 4.1 per 100,000 children <15 years, with marked variation between districts. No children had pre-existing medical conditions. Twenty-three (55%) had disseminated disease, 10 (43%) of whom died. The commonest site of infection was the lungs, which occurred in 21 (50%) children. Other important sites of infection included lymph nodes, spleen, joints and lacrimal glands. Seven (17%) children had bacteremia with no overt focus of infection. Delays in diagnosis and in melioidosis-appropriate antibiotic treatment were observed in nearly 90% of children. Of the clinical isolates tested, 35/36 (97%) were susceptible to gentamicin. Of these, all 11 isolates that were genotyped were of a single multi-locus sequence type, ST881, and possessed the putative B. pseudomallei virulence determinants bimA_Bp, fhaB3, and the YLF gene cluster.

Conclusions

Central Sarawak has a very high incidence of pediatric melioidosis, caused predominantly by gentamicin-susceptible B. pseudomallei strains. Children frequently presented with disseminated disease and had an alarmingly high death rate, despite the absence of any apparent predisposing risk factor.

Melioidosis is a serious, and often fatal community-acquired infection endemic to Southeast Asia and northern Australia. It is caused by the environmental saprophyte Burkholderia pseudomallei, a bacterium that is intrinsically resistant to many commonly used antibiotics. Its presence in Sarawak, Malaysian Borneo, has been documented, and recently, a novel gentamicin-susceptible strain discovered. However, there are limited data on the burden and clinical characteristics of melioidosis in Sarawak, both in adults and in children. In this study, we comprehensively investigated all pediatric melioidosis cases in Central Sarawak over a 6-year period. We found that this region has a very high incidence of pediatric melioidosis, and that children frequently presented with disseminated disease and had high fatality rates, despite the absence of any predisposing risk factor. We confirmed that these infections were caused predominantly by gentamicin-susceptible B. pseudomallei strains. We also highlighted other undescribed epidemiological, clinical and microbiological features, which may help in the overall understanding of B. pseudomallei infections. We emphasized the importance of improving the awareness and recognition of melioidosis in children, both in Sarawak and in other endemic regions.

Melioidosis acquired by a traveler from Papua New Guinea

Melioidosis is an infectious disease caused by Burkholderia pseudomallei. Melioidosis is of public health importance in endemic areas, particularly in tropical and sub-tropical areas. We describe a case of melioidosis contracted by a man with diabetes from Papua New Guinea that was evaluated using multi-locus sequence typing and whole genome sequencing.

Human melioidosis reported by ProMED

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ProMED would be used to assess the reliability of the data of emerging infectious diseases, such as melioidosis.

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The study evaluated the effectiveness of ProMED as a source of epidemiological data by focusing on melioidosis.

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This work identified 4630 cases of melioidosis with an overall case fatality rate of 11%, mainly reported from Australia, Thailand, Singapore, Vietnam, and Malaysia.

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Although certain areas need to be improved, ProMED provided good information about melioidosis.

Objective

There are limited sources describing the global burden of emerging diseases. A review of human melioidosis reported by ProMED was performed and the reliability of the data retrieved assessed in comparison to published reports. The effectiveness of ProMED was evaluated as a source of epidemiological data by focusing on melioidosis.

Methods

Using the keyword ‘melioidosis’ in the ProMED search engine, all of the information from the reports and collected data was reviewed using a structured form, including the year, country, gender, occupation, number of infected individuals, and number of fatal cases.

Results

One hundred and twenty-four entries reported between January 1995 and October 2014 were identified. A total of 4630 cases were reported, with death reported in 505 cases, suggesting a misleadingly low overall case fatality rate (CFR) of 11%. Of 20 cases for which the gender was reported, 12 (60%) were male. Most of the cases were reported from Australia, Thailand, Singapore, Vietnam, and Malaysia, with sporadic reports from other countries.

Conclusions

Internet-based reporting systems such as ProMED are useful to gather information and synthesize knowledge on emerging infections. Although certain areas need to be improved, ProMED provided good information about melioidosis.

Seroepidemiology of melioidosis in children from a remote region of Papua New Guinea

BACKGROUND

The Balimo region in Papua New Guinea has previously been identified as melioidosis-endemic with a predilection for children. Where health resources are scarce, seroepidemiology can be used to assess exposure to Burkholderia pseudomallei and therefore risk of acquiring melioidosis.

METHODS

Logistic regression was used to determine associations between indirect haemagglutination assay (IHA) seroreactivity with environmental and demographic/cultural factors to aid in determining risk factors associated with exposure to B. pseudomallei in children.

RESULTS

Of the 968 participants, 92.9% (899/968) were children, representing the majority of the community school population in the immediate Balimo region. Of these, 24.6% (221/899) were seropositive. Bathing in the lagoon (OR=2.679), drinking from the well or lagoon (OR=1.474), and being a member of the Siboko (OR=1.914) or Wagumisi (OR=1.942) clans were significantly associated with seropositivity. In the multivariate analysis, drinking from a well or lagoon (OR=1.713), and the Siboko (OR=2.341) and Wabadala (OR=2.022) clans were associated with seropositivity.

CONCLUSIONS

This study in children supports observations that interactions with groundwater in this region are risk factors in acquiring melioidosis. Public health measures intended to limit this exposure may help reduce the risk of acquiring melioidosis in this remote community. Associations with clan structure may provide more cultural specific insights, however this requires further elucidation.

Clinical presentation and medical management of melioidosis in children: a 24-year prospective study in the Northern Territory of Australia and review of the literature

BACKGROUND

Melioidosis is less common in children than adults. The clinical spectrum of disease varies greatly between the 2 groups. Treatment guidelines are currently based on adult studies, and revision of existing guidelines is necessary to instruct specific pediatric management.

METHODS

Culture-confirmed cases of melioidosis in the Northern Territory between 1989 and 2013 were identified from the Prospective Melioidosis Study. The epidemiology and clinical spectrum of disease for children aged ≤ 16 years were analyzed and compared with the adult data.

RESULTS

Forty-five pediatric patients were identified, representing 5% of the total 820 melioidosis cases over 24 years. Most children (84%) had no recognized risk factors for melioidosis, and 80% presented during the wet season. Primary cutaneous melioidosis was the commonest presentation in children (60% vs 13%; P < .001), whereas pneumonia predominated in adults (54% vs 20%; P < .001). Bacteremia was less common in children than in adults (16% vs 59%; P < .001). Brainstem encephalitis occurred in 3 children without risk factors. Children were more likely to report an inoculating event (42%; P < .001). There was no difference in mortality between the groups (P = .178), with 3 children dying (7%); all had identifiable risk factors. Four children with cutaneous melioidosis were successfully treated with oral therapy alone, while 2 had skin lesions that resolved spontaneously.

CONCLUSIONS

Pediatric melioidosis commonly manifests as localized cutaneous disease in immunocompetent hosts. The disease can be fatal, especially in individuals with risk factors for disease. Melioidosis with encephalomyelitis can result in severe residual disability. Prompt diagnosis requires a high index of clinical suspicion in endemic areas.

Burkholderia pseudomallei isolates from Sarawak, Malaysian Borneo, are predominantly susceptible to aminoglycosides and macrolides

Melioidosis is a potentially fatal disease caused by the saprophytic bacterium Burkholderia pseudomallei. Resistance to gentamicin is generally a hallmark of B. pseudomallei, and gentamicin is a selective agent in media used for diagnosis of melioidosis. In this study, we determined the prevalence and mechanism of gentamicin susceptibility found in B. pseudomallei isolates from Sarawak, Malaysian Borneo. We performed multilocus sequence typing and antibiotic susceptibility testing on 44 B. pseudomallei clinical isolates from melioidosis patients in Sarawak district hospitals. Whole-genome sequencing was used to identify the mechanism of gentamicin susceptibility. A novel allelic-specific PCR was designed to differentiate gentamicin-sensitive isolates from wild-type B. pseudomallei. A reversion assay was performed to confirm the involvement of this mechanism in gentamicin susceptibility. A substantial proportion (86%) of B. pseudomallei clinical isolates in Sarawak, Malaysian Borneo, were found to be susceptible to the aminoglycoside gentamicin, a rare occurrence in other regions where B. pseudomallei is endemic. Gentamicin sensitivity was restricted to genetically related strains belonging to sequence type 881 or its single-locus variant, sequence type 997. Whole-genome sequencing identified a novel nonsynonymous mutation within amrB, encoding an essential component of the AmrAB-OprA multidrug efflux pump. We confirmed the role of this mutation in conferring aminoglycoside and macrolide sensitivity by reversion of this mutation to the wild-type sequence. Our study demonstrates that alternative B. pseudomallei selective media without gentamicin are needed for accurate melioidosis laboratory diagnosis in Sarawak. This finding may also have implications for environmental sampling of other locations to test for B. pseudomallei endemicity.

Biogeography of Burkholderia pseudomallei in the Torres Strait Islands of Northern Australia

It has been hypothesized that biogeographical boundaries are a feature of Burkholderia pseudomallei ecology, and they impact the epidemiology of melioidosis on a global scale. This study examined the relatedness of B. pseudomallei sourced from islands in the Torres Strait of Northern Australia to determine if the geography of isolated island communities is a determinant of the organisms' dispersal. Environmental sampling on Badu Island in the Near Western Island cluster recovered a single clone. An additional 32 clinical isolates from the region were sourced. Isolates were characterized using multilocus sequence typing and a multiplex PCR targeting the flagellum gene cluster. Gene cluster analysis determined that 69% of the isolates from the region encoded the ancestral Burkholderia thailandensis-like flagellum and chemotaxis gene cluster, a proportion significantly lower than that reported from mainland Australia and consistent with observations of isolates from southern Papua New Guinea. A goodness-of-fit test indicated that there was geographic localization of sequence types throughout the archipelago, with the exception of Thursday Island, the economic and cultural hub of the region. Sequence types common to mainland Australia and Papua New Guinea were identified. These findings demonstrate for the first time an environmental reservoir for B. pseudomallei in the Torres Strait, and multilocus sequence typing suggests that the organism is not randomly distributed throughout this region and that seawater may provide a barrier to dispersal of the organism. Moreover, these findings support an anthropogenic dispersal hypothesis for the spread of B. pseudomallei throughout this region.

Systematic review and consensus guidelines for environmental sampling of Burkholderia pseudomallei

Background

Burkholderia pseudomallei, a Tier 1 Select Agent and the cause of melioidosis, is a Gram-negative bacillus present in the environment in many tropical countries. Defining the global pattern of B. pseudomallei distribution underpins efforts to prevent infection, and is dependent upon robust environmental sampling methodology. Our objective was to review the literature on the detection of environmental B. pseudomallei, update the risk map for melioidosis, and propose international consensus guidelines for soil sampling.

Methods/Principal Findings

An international working party (Detection of Environmental Burkholderia pseudomallei Working Party (DEBWorP)) was formed during the VIth World Melioidosis Congress in 2010. PubMed (January 1912 to December 2011) was searched using the following MeSH terms: pseudomallei or melioidosis. Bibliographies were hand-searched for secondary references. The reported geographical distribution of B. pseudomallei in the environment was mapped and categorized as definite, probable, or possible. The methodology used for detecting environmental B. pseudomallei was extracted and collated. We found that global coverage was patchy, with a lack of studies in many areas where melioidosis is suspected to occur. The sampling strategies and bacterial identification methods used were highly variable, and not all were robust. We developed consensus guidelines with the goals of reducing the probability of false-negative results, and the provision of affordable and ‘low-tech’ methodology that is applicable in both developed and developing countries.

Conclusions/Significance

The proposed consensus guidelines provide the basis for the development of an accurate and comprehensive global map of environmental B. pseudomallei.

Melioidosis is a serious infectious disease caused by the Tier 1 selected agent and Gram-negative environmental saprophyte, Burkholderia pseudomallei. The organism is commonly found in soil and water in melioidosis endemic areas. Infection in humans occurs following bacterial inoculation, inhalation or ingestion. There is a striking lack of accurate information on the global risk of melioidosis, something that could be determined from the global distribution of environmental B. pseudomallei. Soil sampling to detect the presence of B. pseudomallei has been ad hoc, poorly standardized, and the available information poorly collated. Negative studies are almost never reported, and there is no published review on this topic. We responded to this problem during the VI^th World Melioidosis Congress held in Townsville, Australia in December 2010 by forming the ‘Detection of Environmental Burkholderia pseudomallei Working Party (DEBWorP)’. We have since worked together to undertake a systematic review, map the available information, and reach a consensus on low cost methods for the detection of environmental B. pseudomallei. Our goal is to promote the use of these consensus methods and encourage people worldwide to participate in an effort to produce a comprehensive global map of environmental B. pseudomallei.

The global distribution of Burkholderia pseudomallei and melioidosis: an update

While Southeast Asia and northern Australia are well recognized as the major endemic regions for melioidosis, recent reports have expanded the endemic zone. Severe weather events and environmental disasters such as the 2004 Asian tsunami have unmasked locations of sporadic cases and have reconfirmed endemicity in Indonesia. The endemic region now includes the majority of the Indian subcontinent, southern China, Hong Kong and Taiwan. Sporadic cases have occurred in Brazil and elsewhere in the Americas and in island communities such as New Caledonia, in the Pacific Ocean, and Mauritius in the Indian Ocean. Some of the factors that are critical to further elucidating the global distribution of Burkholderia pseudomallei and melioidosis include improved access to diagnostic laboratory facilities and formal confirmation of the identity of bacterial isolates from suspected cases.

Strategies toward vaccines against Burkholderia mallei and Burkholderia pseudomallei

Burkholderia mallei and Burkholderia pseudomallei are Gram-negative, rod-shaped bacteria, and are the causative agents of the diseases glanders and melioidosis, respectively. These bacteria have been recognized as important pathogens for over 100 years, yet a relative dearth of available information exists regarding their virulence determinants and immunopathology. Infection with either of these bacteria presents with nonspecific symptoms and can be either acute or chronic, impeding rapid diagnosis. The lack of a vaccine for either bacterium also makes them potential candidates for bioweaponization. Together with their high rate of infectivity via aerosols and resistance to many common antibiotics, both bacteria have been classified as category B priority pathogens by the US NIH and US CDC, which has spurred a dramatic increase in interest in these microorganisms. Attempts have been made to develop vaccines for these infections, which would not only benefit military personnel, a group most likely to be targeted in an intentional release, but also individuals who may come in contact with glanders-infected animals or live in areas where melioidosis is endemic. This review highlights some recent attempts of vaccine development for these infections and the strategies used to improve the efficacy of vaccine approaches.