Dry-season outbreak of melioidosis in Western Australia

Natural infection of leptospirosis and melioidosis in long-tailed macaques (Macaca fascicularis) in Thailand

This study aimed to determine the incidence of leptospirosis and melioidosis in long-tailed macaques (Macaca fascicularis) in Thailand. Serum samples from 223 monkeys were subjected to the Lepto Latex Test and indirect hemagglutination (IHA) test to detect antibodies against Leptospira spp. and Burkholderia pseudomallei. The microagglutination test (MAT) was used to identify serovars of Leptospira spp. Conventional PCR for the LipL32 gene of L. interogans and the BPSS0120 and btfc-orf18 genes of B. pseudomallei was used for molecular detection. The overall seroprevalence of leptospirosis and melioidosis was 2.69% (95% CI: 0.99-5.76%) and 14.35% (95% CI: 10.03-19.65%), respectively. Six samples that showed positive MAT results were also positive for IHA. The serovars of Leptospira were Ranarum (5/6), Shermani (6/6), and both (5/6). Conventional PCR for the LipL32 gene of Leptospira spp. was positive in 10.31% of the samples (95% CI: 5.56-13.51%). However, there were no positive results for BPSS0120 and btfc-orf18 in B. pseudomallei. Active infection was detected only for leptospirosis; however, it can be assumed that pathogen exposure occurred in this group of animals because immunity could be detected. The routes of infection and elimination pathways of both bacteria remain unclear, and the mechanism of protection in non-human primates needs to be elucidated in further studies. Moreover, this health issue should be considered to prevent human infections in monkeys and their environment.

Screening High-Risk Groups and the General Population for SARS-CoV-2 Nucleic Acids in a Mobile Biosafety Laboratory

The Severe Acute Respiratory Syndrome coronavirus 2 (SARS-CoV-2) pandemic has challenged public health systems worldwide. Therefore, large-scale testing capacity is extremely important diagnosis and exclusion diagnosis. However, fixed laboratories are limited or far away from remote areas. Fortunately, MBS-Lab is characterized by high mobility and rapid on-site detection of SARS-CoV-2 nucleic acid. MBS-Lab was first used in northern Australia during a melioidosis outbreak in 1997. The MBS-Lab and a well-trained diagnostic team were dispatched to Dongchang District, Tonghua City, Jilin Province, China to assist the SARS-CoV-2 virus screening and diagnosis on January 17, 2021. Altogether, 93,952 oropharyngeal swabs samples were collected and tested among the high-risk groups and the general population in Dongchang District. Two single samples were identified as positive in the second turn screening. In the second turn screening, 3 mixed samples (10 in 1) were identified as positive; 10 mixed samples were identified as positive in the third turn screening. By resampling again, one and four cases were identified as positive, respectively. The positive cases were properly isolated and treated in hospital and avoided to visit family members, friends, colleagues and any other persons. Through this way of large-scale screening, human-human spread of SARS-CoV-2 can be effectively avoided. In addition, all staff members strictly executed multiple safety precautions and reduce exposure risks. In the end, none of the staffs was infected with SARS-CoV-2 virus or other pathogens. As an emergency facility for infectious disease control, the MBS-Lab satisfies the requirements of ports and other remote areas far from fixed laboratories and supplements the capabilities of fixed laboratories.

Challenges and perspectives on the use of mobile laboratories during outbreaks and their use for vaccine evaluation

Mobile laboratories provide diagnostic capabilities for routine surveillance and patient identification during an outbreak. In either situation, they face many challenges including identification of the appropriate assay(s) to employ, logistical arrangements, and providing for the health and safety of the laboratory staff. Great strides have been made over the last decade in the development of mobile laboratories with assays that require minimal infrastructure and technical experience. This knowledge and expertise have been developed in partnership with many researchers and public health officials who live in regions prone to infectious disease outbreaks. Mobile laboratories should now also be used in the evaluation of novel vaccines and therapeutics in remote locations. Clinical mobile laboratories will include similar diagnostic capabilities as outbreak response mobile labs, but will also include additional point-of-care instruments operated under Good Clinical Practice guidelines. They will also operate rigorous data management plans so that the data collected will satisfy regulatory agencies during the licensure process. Failure to deploy an adequate clinical mobile laboratory when administering a novel biological product in a remote location is a significant limitation to any collected scientific data that could ultimately undermine clinical development and availability of life-saving interventions.

An improved selective culture medium enhances the isolation of Burkholderia pseudomallei from contaminated specimens

Burkholderia pseudomallei is a Gram-negative environmental bacterium found in tropical climates that causes melioidosis. Culture remains the diagnostic gold standard, but isolation of B. pseudomallei from heavily contaminated sites, such as fecal specimens, can be difficult. We recently reported that B. pseudomallei is capable of infecting the gastrointestinal tract of mice and suggested that the same may be true in humans. Thus, there is a strong need for new culture techniques to allow for efficient detection of B. pseudomallei in fecal and other specimens. We found that the addition of norfloxacin, ampicillin, and polymyxin B to Ashdown's medium (NAP-A) resulted in increased specificity without affecting the growth of 25 B. pseudomallei strains. Furthermore, recovery of B. pseudomallei from human clinical specimens was not affected by the three additional antibiotics. Therefore, we conclude that NAP-A medium provides a new tool for more sensitive isolation of B. pseudomallei from heavily contaminated sites.

The lab without walls: a deployable approach to tropical infectious diseases

The Laboratory Without Walls is a modular field application of molecular biology that provides clinical laboratory support in resource-limited, remote locations. The current repertoire arose from early attempts to deliver clinical pathology and public health investigative services in remote parts of tropical Australia, to address the shortcomings of conventional methods when faced with emerging infectious diseases. Advances in equipment platforms and reagent chemistry have enabling rapid progress, but also ensure the Laboratory Without Walls is subject to continual improvement. Although new molecular biology methods may lead to more easily deployable clinical laboratory capability, logistic and technical governance issues continue to act as important constraints on wider implementation.

Persistent gastric colonization with Burkholderia pseudomallei and dissemination from the gastrointestinal tract following mucosal inoculation of mice

Melioidosis is a disease of humans caused by opportunistic infection with the soil and water bacterium Burkholderia pseudomallei. Melioidosis can manifest as an acute, overwhelming infection or as a chronic, recurrent infection. At present, it is not clear where B. pseudomallei resides in the mammalian host during the chronic, recurrent phase of infection. To address this question, we developed a mouse low-dose mucosal challenge model of chronic B. pseudomallei infection and investigated sites of bacterial persistence over 60 days. Sensitive culture techniques and selective media were used to quantitate bacterial burden in major organs, including the gastrointestinal (GI) tract. We found that the GI tract was the primary site of bacterial persistence during the chronic infection phase, and was the only site from which the organism could be consistently cultured during a 60-day infection period. The organism could be repeatedly recovered from all levels of the GI tract, and chronic infection was accompanied by sustained low-level fecal shedding. The stomach was identified as the primary site of GI colonization as determined by fluorescent in situ hybridization. Organisms in the stomach were associated with the gastric mucosal surface, and the propensity to colonize the gastric mucosa was observed with 4 different B. pseudomallei isolates. In contrast, B. pseudomallei organisms were present at low numbers within luminal contents in the small and large intestine and cecum relative to the stomach. Notably, inflammatory lesions were not detected in any GI tissue examined in chronically-infected mice. Only low-dose oral or intranasal inoculation led to GI colonization and development of chronic infection of the spleen and liver. Thus, we concluded that in a mouse model of melioidosis B. pseudomallei preferentially colonizes the stomach following oral inoculation, and that the chronically colonized GI tract likely serves as a reservoir for dissemination of infection to extra-intestinal sites.

The aftermath of the Western Australian melioidosis outbreak

Melioidosis became a notifiable disease in Western Australia (WA) 2 years after the West Kimberley melioidosis outbreak. Two cases of melioidosis caused by the outbreak genotype of Burkholderia pseudomallei (National Collection of Type Cultures [NCTC] 13177) occurred in 1998 and 1999 in persons who visited the outbreak location at the time. No other infections caused by the outbreak strain have been recorded in WA since that time, despite an average of four culture-positive cases per year. Sporadic cases of melioidosis often follow tropical storms and cyclones during summer, and they have been detected outside the endemic area when cyclones travel far inland. In 2007, environmental isolates resembling NCTC 13177 were found 500 km east of the outbreak location after unusually severe weather. Recent whole-genome analysis places NCTC 13177 genetically close to other Australian isolates. Additional biogeographic and ecological studies are needed to establish the relative importance of environmental cofactors in disease pathogenesis.

Pathogenicity of high-dose enteral inoculation of Burkholderia pseudomallei to mice

Melioidosis is a frequently lethal tropical infection caused by the environmental saprophyte Burkholderia pseudomallei. Although transcutaneous inoculation and inhalation are considered the primary routes of infection, suggestive clinical evidence implicates ingestion as a possible alternative route. We show that in BALB/c and C57BL/6 mice, direct gastric inoculation of high doses of B. pseudomallei causes systemic infection that may be lethal or cause chronic disseminated infection. Mice may shed bacteria in the stool for weeks after infection, and high titers of B. pseudomallei-specific IgG are detectable. This report of enteric murine melioidosis supports further consideration of this route of infection.

High-redundancy draft sequencing of 15 clinical and environmental Burkholderia strains

The Gram-negative Burkholderia genus includes several species of intracellular bacterial pathogens that pose substantial risk to humans. In this study, we have generated draft genome sequences of 15 strains of B. oklahomensis, B. pseudomallei, B. thailandensis, and B. ubonensis to an average sequence read coverage of 25- to 40-fold.

The survival of Burkholderia pseudomallei in liquid media

We studied the effect of environmental parameters on the survival of Burkholderia pseudomallei. There was a small increase in bacterial count for up to 28 days in sterilized distilled water or rain water, in water at 20 degrees C or 40 degrees C, and in buffered solutions of pH 4 or higher. Counts of culturable B. pseudomallei declined at pH 3, in the presence of seawater or water with concentrations of 4% salt or higher, and under refrigeration. The morphological appearances of B. pseudomallei changed under conditions that maintained culturable numbers from bacilli to coccoid cells and spiral forms under pH or salt stress. These observations indicate that B. pseudomallei can endure nutrient-depleted environments as well as a wide range of pH, salt concentrations, and temperatures for periods of up to 28 days. The relative stability of B. pseudomallei under these conditions underlines the tenacity of this species and its potential for natural dispersal in water: in surface water collections, in managed water distribution systems, and through rainfall. These survival properties help explain the recent expansion of the known melioidosis endemic zone in Australia and may have played a part in recent melioidosis outbreaks.

Inactivation of virulent Burkholderia pseudomallei by sunlight

The goal of this study was to determine the sensitivity of virulent Burkholderia pseudomallei to natural sunlight. We describe solar dosimetry calibrated to integrate radiation between 295 and 305 nm and an exposure system that minimizes thermal effects on bacterial cells. Burkholderia pseudomallei cells were either exposed to sunlight in UV transparent dishes or maintained in the dark covered by opaque foil. The cells maintained in the dark remained at constant levels for the duration of all experiments. The exposed cells nearby were killed with a kinetic studied through 5 Log10 inactivation. We found that cells in stationary phase of growth were nearly two-fold more resistant to sunlight than cells in lag or exponential growth. A virulent strain of B. pseudomallei that produced mucoid colonies showed sensitivity to sunlight similar to both a virulent strain that produced nonmucoid colonies and a strain of B. thailandensis. The inactivation of B. pseudomallei by sunlight in different types of water of environmental relevance or inside amoebae was investigated. The sensitivity of virulent B. pseudomallei was calculated and its comparison with previous studies employing monochromatic germicidal light (254 nm) is discussed. This may be the first report in the open literature of the inactivation of a virulent biological threat agent by natural sunlight. These data should assist in estimating the risk for contracting melioidosis and in predicting the time period during which B. pseudomallei remains infectious after an accidental or intentional release in the environment.

Principia ætiologica: taking causality beyond Koch's postulates

There is no single accepted method to establish a causal relationship between an infective agent and its corresponding infectious disease. Different biomedical disciplines use a patchwork of distinct but overlapping approaches. To a greater or lesser extent these are based on criteria known as the Koch–Henle postulates, or ‘Koch's postulates' for short. Deficiencies in Koch's postulates were recognized by their principal author shortly after their formulation. Now, over a century later, a more rigorous method to test causality has still to be finalized. One contender is a method that uses molecular methods to establish a causal relationship (‘molecular Koch's postulates'). Recognizing the wider range of contemporary approaches used to build an argument for a causal relationship, the use of a more inclusive approach to establish proof of causality is proposed. This method uses an argument built from a series of assertions. Assertion 1: congruence or reproducible correlation of a taxonomically defined life form with the clinico-pathological and epidemiological features of infection. Assertion 2: consistency of the demonstrable biological response in the subject to an encounter with the prospective infective agent. Assertion 3: progressive or cumulative dissonance as an explanation for pathophysiological processes at every known level of biological organization in the subject. Assertion 4: curtailment of that pathophysiological process on the deliberate introduction of a specified biomedical intervention. Evidence to implicate the candidate biological entity as an initiator of or primer for cumulative dissonance places it in a subcategory of micro-organisms to be known as ‘priobes’. A priobe is the sufficient and necessary antecedent cause of a pathophysiological process evident as an infectious disease.

Melioidosis in New Caledonia

Recognized melioidosis-endemic areas are widening. In the South Pacific, melioidosis is endemic in New Caledonia, northern Australia, and Papua New Guinea. We report the first 4 documented cases of human melioidosis from New Caledonia. Molecular typing of 2 Burkholderia pseudomallei isolates suggests a link to Australian strains.

Cellular fatty acid profile distinguishes Burkholderia pseudomallei from avirulent Burkholderia thailandensis

Burkholderia pseudomallei, the cause of melioidosis, can be distinguished from the closely related but nonpathogenic Burkholderia thailandensis by gas chromatography (GC) analysis of fatty acid derivatives. A 2-hydroxymyristic acid derivative (14:0 2OH) was present in 95% of B. pseudomallei isolates and no B. thailandensis isolates. GC mass spectrophotometry confirmed that 2-hydroxymyristic acid was present in B. pseudomallei. GC-fatty acid methyl ester analysis may be useful in distinguishing these two closely related species.

Novel selective medium for isolation of Burkholderia pseudomallei

Isolation of Burkholderia pseudomallei currently relies on the use of Ashdown's selective agar (ASA). We designed a new selective agar (Burkholderia pseudomallei selective agar [BPSA]) to improve recovery of the more easily inhibited strains of B. pseudomallei. B. pseudomallei, Burkholderia cepacia, and Pseudomonas aeruginosa were used to determine the selectivity and sensitivity of BPSA. BPSA was more inhibitory to P. aeruginosa and B. cepacia and should make recognition of Burkholderia species easier due to distinctive colony morphology. BPSA also inhibited Enterococcus, Escherichia, Staphylococcus, and Streptococcus: These results indicate that BPSA is a potential replacement for ASA.

Ecology of Burkholderia pseudomallei and the interactions between environmental Burkholderia spp. and human-animal hosts

Early workers thought that melioidosis was a zoonosis with a reservoir in rodents, but we now know that Burkholderia pseudomallei is a widely distributed environmental saprophyte. In northeast Thailand, two thirds of paddy fields yield the organism, and 80% of children have antibodies by the time they are 4 years old. However, interpretation of these results has been complicated by the recent recognition of avirulent, antigenically cross-reacting environmental organisms for which the name B. thailandensis has been proposed. We still know very little about the climatic, physical, chemical and biological factors which control the proliferation and survival of Burkholderia spp. in the environment, although epidemiological studies show space-time clustering of melioidosis. It is assumed that most human and animal melioidosis arises through exposure to contaminated soil or muddy water, although only 6% of human cases have a clear history of inoculation, and a further 0.5% of cases follow near-drowning. Laboratory animals have also been infected by ingestion, inhalation and insect bites, but evidence of infection acquired naturally by these routes remains anecdotal. Sporadic cases have resulted from iatrogenic inoculation, laboratory accidents, and person-to-person or animal-to-person spread. Whether exposure to B. pseudomallei will result in disease probably depends on the balance between the virulence of the strain, the immune status of the host (e.g. diabetes mellitus) and the size of the inoculum.

The epidemiology of melioidosis in Australia and Papua New Guinea

Melioidosis was first described in Australia in an outbreak in sheep in 1949 in north Queensland (22 degrees S). Human melioidosis was first described from Townsville (19 degrees S) in 1950. Melioidosis is hyperendemic in the Top End of the Northern Territory (NT) and as in parts of northeastern Thailand it is the commonest cause of fatal community-acquired septicemic pneumonia. In the 9 years since 1989 the prospective NT melioidosis study at Royal Darwin Hospital (12 degrees S) has documented 206 culture confirmed cases of melioidosis, with an average annual incidence of 16.5/100,000. Melioidosis is also seen in the north of Western Australia and north Queensland, including the Torres Strait Islands, but is uncommon in adjacent Papua New Guinea. Serological studies suggest that infection is rare in the Port Moresby region, but there is emerging evidence of melioidosis from Western Province. The NT study has documented inoculating events in 52 (25%) of cases, with an incubation period of 1-21 days (mean 9 days); 84% of cases had acute disease from presumed recent acquisition and 13% had chronic disease (sick, > 2 months). In 4% there was evidence of possible reactivation from a latent focus; 28 of 153 (18%) males had prostatic abscesses. The overall mortality was 21% (43 cases), with a mortality rate in septicemic cases (95) of 39% and in non-septicemic cases (103) of 4%. Pneumonia was the commonest presentation in both groups and, in addition, eight patients (two deaths) presented with melioidosis encephalomyelitis. Melioidosis clusters in temperate Australia are attributed to animals imported from the north. Molecular typing of Burkholderia pseudomallei isolates from temperate southwest Western Australia showed clonality over 25 years. In this outbreak and in studies from the NT, some soil isolates are molecularly identical to epidemiologically related animal and human isolates. Molecular typing has implicated the water supply in two clonal outbreaks in remote aboriginal communities in northern Australia. Further prospective collaborative studies are required to evaluate whether there are truly regional differences in clinical features of melioidosis and to better understand how B. pseudomallei is acquired from the environment.