Recrudescent melioidosis: a southeast asian legacy

Cohort profile: a migratory cohort study of US Marines who train in Australia

PURPOSE

In 2012, US Marines and Sailors began annual deployments to Australia to participate in joint training exercises with the Australian Defence Force and other partners in the region. During their training, US service members are exposed to a variety of infectious disease threats not normally encountered by American citizens. This paper describes a cohort of US Marines and Sailors enrolled during five rotations to Australia between 2016 and 2020.

PARTICIPANTS

Study participation is strictly voluntary. Group informational sessions are held prior to deployment to describe the study structure and goals, as well as the infectious disease threats that participants may encounter while in Australia. All participants provided written informed consent. Consented participants complete a pre-deployment questionnaire to collect data including basic demographic information, military occupational specialty, travel history, family history, basic health status and personal habits such as alcohol consumption. Blood is collected for serum, plasma and peripheral blood mononuclear cells (PBMC) processing. Data and specimen collection is repeated up to three times: before, during and after deployment.

FINDINGS TO DATE

From the five rotations that comprised the 2016-2020 Marine Rotational Force-Darwin, we enrolled 1289 volunteers. Enrolments during this period were overwhelmingly white male under the age of 24 years. Most of the enrollees were junior enlisted and non-commissioned officers, with a smaller number of staff non-commissioned officers and commissioned officers, and minimal warrant officers. Over half of the enrollees had occupational specialty designations for infantry.

FUTURE PLANS

In the future, we will screen samples for serological evidence of infection with Burkholderia pseudomallei, Coxiella burnetii, Ross River virus, SARS-CoV-2 and other operationally relevant pathogens endemic in Australia. Antigenic stimulation assays will be performed on PBMCs collected from seropositive individuals to characterise the immune response to these infections in this healthy American population.

Indirect Detection of Burkholderia pseudomallei Infection in a US Marine After Training in Australia

In 2012, the United States Marine Corps began annual deployments around Australia, including highly endemic areas for Burkholderia pseudomallei. B. pseudomallei infection, or melioidosis, is difficult to diagnose, and culture remains the gold standard. Accurate and timely diagnosis is essential, however, to ensuring appropriate therapy. Ten days after returning from Australia, a Marine presented to a community hospital with massive cervical lymphadenopathy, fever, and cough. Computed tomography demonstrated scattered pulmonary infiltrates with small cavitations; lymphadenopathy involving the cervical, supraclavicular, and mediastinal nodes; and splenomegaly. Sputum and blood cultures were negative. Empiric antimicrobial therapy with ceftazidime was initiated for suspected melioidosis. Retrospectively, a prototype iSTAT cartridge modified to detect B. pseudomallei capsular polysaccharide antigen was used to test a specimen of the patient's blood and was determined to be positive. Over the course of therapy, B. pseudomallei capsular antigen levels in blood declined as the patient improved. The leveraging of an existing point-of-care (POC) analyzer to create a rapid diagnostic assay for melioidosis provides a template for rapid POC diagnostics that could significantly improve the ability of clinicians to deliver timely and appropriate therapy for serious infections.

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

The first cases of human melioidosis were described in Vietnam in the 1920s, almost a century ago. It was in Vietnam in the thirties that the saprophytic nature of B. pseudomallei was first recognized. Although a significant number of French and U.S. soldiers acquired the disease during the Vietnam wars, indigenous cases in the Vietnamese population were only sporadically reported over many decades. After reunification in 1975, only two retrospective studies reported relatively small numbers of indigenous cases from single tertiary care hospitals located in the biggest cities in the South and the North, respectively. Studies from provincial hospitals throughout the country were missing until the Research Network on Melioidosis and Burkholderia pseudomallei (RENOMAB) project started in 2014. From then on seminars, workshops, and national scientific conferences on melioidosis have been conducted to raise awareness among physicians and clinical laboratory staff. This led to the recognition of a significant number of cases in at least 36 hospitals in 26 provinces and cities throughout Vietnam. Although a widespread distribution of melioidosis has now been documented, there are still challenges to understand the true epidemiology of the disease. Establishment of national guidelines for diagnosis, management, and reporting of the disease together with more investigations on animal melioidosis, genomic diversity of B. pseudomallei and its environmental distribution are required.

Splenic abscesses in a returning traveler

Burkholderia, an aerobic gram-negative rod, is the causative organism behind melioidosis and is a common soil and water organism found predominantly in South-East Asia. We report the case of a 68 year-old man returning from an extended trip to the Philippines, with splenic hypodense lesions on abdominal computer tomography scan, later confirmed to be culture-positive for Burkholderia pseudomallei. The patient was treated with a course of intravenous ceftazidime followed by eradication therapy with oral doxycycline and trimethoprim-sulfamethoxazole. He recovered with complete resolution of symptoms at follow up. In a returning traveler from an endemic area, melioidosis should be considered as part of the differential for any febrile illness with abscesses.

Spectrum of imaging findings in melioidosis

This pictorial review aims to highlight the clinical and imaging features of melioidosis in various organ systems. The patients were from two centres: one in Thailand and one in Singapore. The annual average incidence of melioidosis is estimated to be 4.4 in 100 000 in north-eastern Thailand and 1.7 in 100 000 in Singapore. Melioidosis affects many different organs and produces a spectrum of imaging features. The lung is the most frequently involved organ and, on radiographs and computed tomography, melioidosis may manifest as acute pulmonary consolidation, multiple nodules and abscesses. The finding of multiple small discrete abscesses in both the liver and the spleen is highly suggestive of visceral melioidosis and is best diagnosed on ultrasonography and computed tomography. Bone and soft tissue musculoskeletal involvement is usually part of disseminated melioidosis, with changes being seen on radiographs and MRI. Although imaging findings of melioidosis are not specific, this infection requires a high index of clinical suspicion, particularly in patients with pre-disposing comorbidities, such as diabetes mellitus, chronic renal failure, alcoholism or malignancy, those who are immunosuppressed as the result of either diseases or drug treatment, and those living in or with a history of travel to endemic areas.

Clinical guideline for diagnosis and management of melioidosis

Melioidosis is an emerging infection in Brazil and neighbouring South American countries. The wide range of clinical presentations include severe community-acquired pneumonia, septicaemia, central nervous system infection and less severe soft tissue infection. Diagnosis depends heavily on the clinical microbiology laboratory for culture. Burkholderia pseudomallei, the bacterial cause of melioidosis, is easily cultured from blood, sputum and other clinical samples. However, B. pseudomallei can be difficult to identify reliably, and can be confused with closely related bacteria, some of which may be dismissed as insignificant culture contaminants. Serological tests can help to support a diagnosis of melioidosis, but by themselves do not provide a definitive diagnosis. The use of a laboratory discovery pathway can help reduce the risk of missing atypical B. pseudomallei isolates. Recommended antibiotic treatment for severe infection is either intravenous Ceftazidime or Meropenem for several weeks, followed by up to 20 weeks oral treatment with a combination of trimethoprim-sulphamethoxazole and doxycycline. Consistent use of diagnostic microbiology to confirm the diagnosis, and rigorous treatment of severe infection with the correct antibiotics in two stages; acute and eradication, will contribute to a reduction in mortality from melioidosis.

Mélioïdose

Melioidosis is an emerging zoonosis, due to Burkholderia pseudomallei, which is a highly invasive, resistant, and resilient soil bacteria, transmitted by cutaneous or airborne route, and is a potential weapon for bioterrorism. Although the agent has been identified all over the world, the human disease is endemic only in SE Asia and Northern Australia, and gained recent interest after the December 2004 tsunami. Human infection can be a very severe systemic disease (mortality 20 to 80%), with protean expression, but the lung is the most affected organ (50%). Pathophysiology remains unclear. Diabetes mellitus is a major risk factor, and is present in half the Asian patients with melioidosis. Recommended antibiotic regimens are expensive, and in severe disease should be prolonged to 20 weeks to reduce the risk of relapse. Prospects for prevention are limited, and no vaccine is available yet.

Genomic plasticity of the causative agent of melioidosis, Burkholderia pseudomallei

Burkholderia pseudomallei is a recognized biothreat agent and the causative agent of melioidosis. This Gram-negative bacterium exists as a soil saprophyte in melioidosis-endemic areas of the world and accounts for 20% of community-acquired septicaemias in northeastern Thailand where half of those affected die. Here we report the complete genome of B. pseudomallei, which is composed of two chromosomes of 4.07 megabase pairs and 3.17 megabase pairs, showing significant functional partitioning of genes between them. The large chromosome encodes many of the core functions associated with central metabolism and cell growth, whereas the small chromosome carries more accessory functions associated with adaptation and survival in different niches. Genomic comparisons with closely and more distantly related bacteria revealed a greater level of gene order conservation and a greater number of orthologous genes on the large chromosome, suggesting that the two replicons have distinct evolutionary origins. A striking feature of the genome was the presence of 16 genomic islands (GIs) that together made up 6.1% of the genome. Further analysis revealed these islands to be variably present in a collection of invasive and soil isolates but entirely absent from the clonally related organism B. mallei. We propose that variable horizontal gene acquisition by B. pseudomallei is an important feature of recent genetic evolution and that this has resulted in a genetically diverse pathogenic species.

Melioidotic septic arthritis and its risk factors

BACKGROUND

Melioidotic septic arthritis is an infection caused by the gram-negative bacillus Burkholderia pseudomallei. It is commonly found in Northeast Thailand. The goal of our study was to identify specific characteristics of patients with melioidotic septic arthritis by comparing them with patients with non-melioidotic septic arthritis and to describe the results of treatment of melioidotic septic arthritis.

METHODS

We conducted a retrospective study of seventy-seven patients with septic arthritis who were treated in our hospital over a period of four years. Twenty-five of the patients had melioidotic septic arthritis, and fifty-two had non-melioidotic septic arthritis. Univariate and multivariate analyses were conducted to identify the risk factors for melioidotic septic arthritis, and the clinical course of the twenty-five patients with melioidotic septic arthritis was followed until the infection resolved.

RESULTS

Patients with melioidotic septic arthritis differed significantly (p = 0.002 ) from those with non-melioidotic septic arthritis with regard to the frequency of diabetes mellitus and of involvement of an upper-extremity joint. The odds ratio that melioidosis was the cause of the infection was 15.7 (95% confidence interval, 4.5 to 55.6) in a patient with diabetes mellitus and 4.51 (95% confidence interval, 1.04 to 19.65) in a patient with involvement of an upper-extremity joint. Twenty-two of the twenty-five patients with melioidotic septic arthritis responded to treatment, which consisted of six months of antibiotic therapy combined with needle aspiration, as well as surgical drainage of the affected joint when necessary (sixteen patients).

CONCLUSIONS

A diagnosis of melioidotic septic arthritis should be considered when septic arthritis is seen in an individual who is indigenous to or has recently visited Southeast Asia. The infection is more likely to be melioidotic septic arthritis if it involves an upper-extremity joint and if the patient has diabetes mellitus.

Melioidosis

Melioidosis, which is infection with the gram-negative bacterium Burkholderia pseudomallei, is an important cause of sepsis in east Asia and northern Australia. In northeastern Thailand, melioidosis accounts for 20% of all community-acquired septicaemias, and causes death in 40% of treated patients. B pseudomallei is an environmental saprophyte found in wet soils. It mostly infects adults with an underlying predisposing condition, mainly diabetes mellitus. Melioidosis is characterised by formation of abscesses, especially in the lungs, liver, spleen, skeletal muscle, and prostate. In a third of paediatric cases in southeast Asia, the disease presents as parotid abscess. In northern Australia, 4% of patients present with brain stem encephalitis. Ceftazidime is the treatment of choice for severe melioidosis, but response to high dose parenteral treatment is slow (median time to abatement of fever 9 days). Maintenance antibiotic treatment is with a four-drug regimen of chloramphenicol, doxycycline, and trimethoprim-sulfamethoxazole, or with amoxicillin-clavulanate in children and pregnant women. However, even with 20 weeks' antibiotic treatment, 10% of patients relapse. With improvements in health care and diagnostic microbiology in endemic areas of Asia, and increased travel, melioidosis will probably be recognised increasingly during the next decade.

Interaction between Burkholderia pseudomallei and Acanthamoeba species results in coiling phagocytosis, endamebic bacterial survival, and escape

Burkholderia pseudomallei causes melioidosis, a potentially fatal disease whose clinical outcomes include rapid-onset septicemia and relapsing and delayed-onset infections. Like other facultative intracellular bacterial pathogens, B. pseudomallei is capable of survival in human phagocytic cells, but unlike mycobacteria, Listeria monocytogenes, and Salmonella serovar Typhimurium, the species has not been reported to survive as an endosymbiont in free-living amebae. We investigated the consequences of exposing Acanthamoeba astronyxis, A. castellani, and A. polyphaga to B. pseudomallei NCTC 10276 in a series of coculture experiments. Bacterial endocytosis was observed in all three Acanthamoeba species. A more extensive range of cellular interactions including bacterial adhesion, incorporation into amebic vacuoles, and separation was observed with A. astronyxis in timed coculture experiments. Amebic trophozoites containing motile intravacuolar bacilli were found throughout 72 h of coculture. Confocal microscopy was used to confirm the intracellular location of endamebic B. pseudomallei cells. Transmission electron microscopy of coculture preparations revealed clusters of intact bacilli in membrane-lined vesicles inside the trophozoite cytoplasm; 5 x 10(2) CFU of bacteria per ml were recovered from lysed amebic trophozoites after 60 min of coculture. Demonstration of an interaction between B. pseudomallei and free-living acanthamebae in vitro raises the possibility that a similar interaction in vivo might affect environmental survival of B. pseudomallei and subsequent human exposure. Endamebic passage of B. pseudomallei warrants further investigation as a potential in vitro model of intracellular B. pseudomallei infection.

Detection of Burkholderia pseudomallei in blood samples using polymerase chain reaction

A highly sensitive, specific, rapid and simple method to detect Burkholderia pseudomallei in blood samples was developed. Two 22-base oligonucleotide primers, based on sequences from a specific DNA probe, were used for amplification of bacterial DNA by the polymerase chain reaction (PCR). Amplification with these primers yielded a 178-base pair product in 100 clinical isolates of B. pseudomallei. As little as 0.5 fg of B. pseudomallei DNA was detectable by this method. Experiments involving inoculation of the organism into uninfected blood samples showed that the method could be used to detect as few as 1 bacterial cell ml-1 of whole blood. Non-specific amplification of other bacterial DNAs from 18 samples of bacteria was not observed. Blood samples from seven patients proven to have melioidosis by haemoculture were positive using these primers. The total time required for sample processing, amplification and visualization was approximately 3.5 h. The high sensitivity, rapidity and simplicity of this method should make it valuable for diagnosis, monitoring of drug treatment and for epidemiological studies of the melioidosis.

Pulmonary melioidosis

Melioidosis is the name given to all diseases caused by the bacterium Pseudomonas pseudomallei. Melioidosis is a tropical disease and prevails in parts of Southeast Asia, northern Australia, and Central and South America. However, in recent years, cases of melioidosis have been reported in the United States and other areas. The organism can infect any organ system, although the lung is the most common organ affected. Pulmonary melioidosis presents either as an acute fulminant pneumonia or as an indolent cavitary disease. In northeastern Thailand, the incidence of P pseudomallei infection is extremely high with significant mortality. One of the key problems with treating melioidosis is its recalcitrance to therapy and high relapse rate. In addition, this Gram-negative rod is resistant to aminoglycosides. In nonendemic regions, patients with melioidosis more typically present with reactivation disease occurring months to years after initial exposure to the organism. The pulmonary disease is mainly in the apices and resembles tuberculosis. With the increasing mobility of people throughout the world and the influx of immigrants from endemic to nonendemic areas, it is important that clinicians be aware of this disease. This article will review the epidemiology, clinical presentations, diagnosis, and treatment of pulmonary melioidosis.

Prevalence of antibodies to Pseudomonas pseudomallei exotoxin and whole cell antigens in military personnel in Sabah and Sarawak, Malaysia

Sera from 420 military personnel serving in Sabah and Sarawk, Malaysia, were tested for antibodies to Pseudomonas pseudomallei exotoxin and whole cell antigens by enzyme-linked immunosorbent assay procedure (ELISA). Data showed that 54.4% of serum samples were positive for antibodies to P. pseudomallei exotoxin and 65.7% were positive for antibodies to the whole cell antigens. Samples gave much lower titers for anti-exotoxin antibodies compared to titers against crude whole cell antigens. The incidence of antibody to exotoxin was highest in the age groups ranging from 26 to 32 years, where the positive rates were higher than 40% and 30% for military personnel serving in Sarawak and Sabah, respectively.

Melioidosis: the tip of the iceberg?

For nearly 80 years clinical melioidosis has been considered a rare disease. This bacterial infection is caused by Pseudomonas pseudomallei, a saprophyte found in soil and surface water of endemic areas. Consequently, those who have most contact with soil, the rural poor, are likely to be at greatest risk of infection. Since the diversity of clinical manifestations necessitates the isolation and identification of the causative organism for a definitive diagnosis of melioidosis and the population at greatest risk within endemic areas rarely have access to an appropriate level of health care, the disease has probably been underrecognized. Melioidosis is now known to be an important cause of human morbidity and mortality in Thailand, and this may be true throughout Southeast Asia, which is usually regarded as the main endemic area for the disease. In Australia, melioidosis causes a smaller number of human infections, while disease among livestock has important economic and possible public health implications. Sporadic reports of the infection indicate its presence in several other tropical regions: in the Indian subcontinent, Africa, and Central and South America. Clinical melioidosis may be highly prevalent in these areas, but underdiagnosed as a result of a lack of awareness of the clinical and microbiological features of the disease, or simply because of a lack of health care facilities. Furthermore, during the last two decades the importation and transmission of melioidosis within nontropical zones have been documented. The causative organism is not difficult to grow, and modern antibiotics have improved disease prognosis. Further studies are needed to determine the true worldwide distribution and prevalence of melioidosis so that improved therapeutic and preventive measures can be developed and applied.

Inhibition of macromolecular synthesis in cultured macrophages by Pseudomonas pseudomallei exotoxin

Pseudomonas pseudomallei exotoxin was found to be a potent inhibitor of protein and DNA synthesis in cultured macrophages. Inhibition of DNA synthesis occurred at toxin concentrations as low as 1-2 micrograms/ml and inhibition of 3H-thymidine uptake was almost complete at concentrations of 8 micrograms/ml or more. A close correlation between cell damage and inhibition by DNA synthesis was observed. For protein synthesis, inhibition was obtained at much lower doses (0.06-2.0 micrograms/ml) of the toxin. At similar toxin concentrations, DNA synthesis was marginally affected. Further, it was shown that protein synthesis inhibition occurred almost immediately after incubation, reaching its maximal inhibitory effect of 70% after 6 hr. DNA synthesis, however, was minimally affected by a similar toxin concentration even after 10 hr of incubation. The inhibition of macromolecular synthesis in macrophages by P. pseudomallei exotoxin may be relevant to its modulatory effect on the host defense mechanism.

Melioidosis: a reminder

Recrudescent pulmonary melioidosis developed in two patients 12 and 16 years after their last travels to an endemic area. In one, a clinically silent prostatic abscess may have been the focus; and in both, the diagnosis was difficult to make even when the laboratory was notified of the possibility of infection with Pseudomonas pseudomallei. Recrudescent melioidosis should be considered in febrile patients who have been in endemic areas regardless of the interval from last exposure to the development of disease.

A retrospective serological suvey of Royal Marines previously exposed to Pseudomonas pseudomallei in South East Asia

Following the suggestion that it was possible that cases of melioidosis amongst those who had been exposed abroad in the past, might be escaping notice, 487 Royal Marines were examined by indirect haemagglutination studies. Four hundred and eleven of these subjects had served for variable times in areas where melioidosis has been known to occur in Indonesia and Malaya, between 1960 and 1974, occupied in activities in the jungle and paddy fields during which exposure to the disease was to be expected. No evidence of residual subclinical melioidosis was found and it seems unlikely that recrudescent disease will prove to be a problem in the future for English servicemen who have been in South East Asia.

Melioidosis: recrudescence associated with bronchogenic carcinoma twenty-six years following initial geographic exposure

Melioidosis was diagnosed in association with lung cancer in a World War 2 veteran 26 years after geographic exposure. The case history illustrates the prolonged latency, difficult diagnosis, and resistance to therapy of chronic melioidosis. Implications are that chronic forms of the disease will continue to surface in veterans of Southeast Asian conflicts for decades.