Glanders-A Re-emerging Zoonotic Disease: A Review

Protein Microarray-Guided Development of a Highly Sensitive and Specific Dipstick Assay for Glanders Serodiagnostics

Burkholderia mallei, the causative agent of glanders, is a clonal descendant of Burkholderia pseudomallei, the causative agent of melioidosis, which has lost its environmental reservoir and has a restricted host range. Despite limitations in terms of sensitivity and specificity, complement fixation is still the official diagnostic test for glanders. Therefore, new tools are needed for diagnostics and to study the B. mallei epidemiology. We recently developed a highly sensitive serodiagnostic microarray test for human melioidosis based on the multiplex detection of B. pseudomallei proteins. In this study, we modified our array tests by using anti-horse IgG conjugate and tested sera from B. mallei-infected horses (n = 30), negative controls (n = 39), and horses infected with other pathogens (n = 14). Our array results show a sensitivity of 96.7% (confidence interval [CI] 85.5 to 99.6%) and a specificity of 100.0% (CI, 95.4 to 100.0%). The reactivity pattern of the positive sera on our array test allowed us to identify a set of 12 highly reactive proteins of interest for glanders diagnosis. The B. mallei variants of the three best protein candidates were selected for the development of a novel dipstick assay. Our point-of-care test detected glanders cases in less than 15 min with a sensitivity of 90.0% (CI, 75.7 to 97.1%) and a specificity of 100.0% (CI, 95.4 to 100.0%). The microarray and dipstick can easily be adopted for the diagnosis of both B. mallei and B. pseudomallei infections in different animals. Future studies will show whether multiplex serological testing has the potential to differentiate between these pathogens.

Expression of virulence and antimicrobial related proteins in Burkholderia mallei and Burkholderia pseudomallei

BACKGROUND

Burkholderia mallei and Burkholderia pseudomallei are both potential biological threat agents. Melioidosis caused by B. pseudomallei is endemic in Southeast Asia and Northern Australia, while glanders caused by B. mallei infections are rare. Here we studied the proteomes of different B. mallei and B. pseudomallei isolates to determine species specific characteristics.

METHODS

The expressed proteins of 5 B. mallei and 6 B. pseudomallei strains were characterized using liquid chromatography high-resolution tandem mass spectrometry (LC-HRMS/MS). Subsequently, expression of potential resistance and virulence related characteristics were analyzed and compared.

RESULTS

Proteome analysis can be used for the identification of B. mallei and B. pseudomallei. Both species were identified based on >60 discriminative peptides. Expression of proteins potentially involved in antimicrobial resistance, AmrAB-OprA, BpeAB-OprB, BpeEF-OprC, PenA as well as several other efflux pump related proteins and putative β-lactamases was demonstrated. Despite, the fact that efflux pump BpeAB-OprB was expressed in all isolates, no clear correlation with an antimicrobial phenotype and the efflux-pump could be established. Also consistent with the phenotypes, no amino acid mutations in PenA known to result in β-lactam resistance could be identified. In all studied isolates, the expression of virulence (related) factors Capsule-1 and T2SS was demonstrated. The expression of T6SS-1 was demonstrated in all 6 B. pseudomallei isolates and in 2 of the 5 B. mallei isolates. In all, except one B. pseudomallei isolate, poly-beta-1,6 N-acetyl-D-glucosamine export porin (Pga), important for biofilm formation, was detected, which were absent in the proteomes of B. mallei. Siderophores, iron binding proteins, malleobactin and malleilactone are possibly expressed in both species under standard laboratory growth conditions. Expression of multiple proteins from both the malleobactin and malleilactone polyketide synthase (PKS) and non-ribosomal peptide synthetase (NRPS) clusters was demonstrated in both species. All B. pseudomallei expressed at least seven of the nine proteins of the bactobolin synthase cluster (bactobolin, is a ribosome targeting antibiotic), while only in one B. mallei isolate expression of two proteins of this synthase cluster was identified.

CONCLUSIONS

Analyzing the expressed proteomes revealed differences between B. mallei and B. pseudomallei but also between isolates from the same species. Proteome analysis can be used not only to identify B. mallei and B. pseudomallei but also to characterize the presence of important factors that putatively contribute to the pathogenesis of B. mallei and B. pseudomallei.

One Health surveillance approaches for melioidosis and glanders: The Malaysian perspective

The One Health concept was initiated to promote the integration of human, animal, and environmental ecosystems into healthcare to ensure effective control and the sustainable governance of multifaceted health matters. Climate change, deforestation, and rigorous farming disrupt the environment, which serves as the natural habitat for many animals and microbes, increasing the likelihood of disease transmission between humans and animals. Melioidosis (neglected tropical diseases) and glanders are of humans and animals caused by the gram-negative bacteria Burkholderia pseudomallei and its close relative Burkholderia mallei, respectively. In Malaysia, although melioidosis is endemic, it is not a notifiable disease. Hence, the true prevalence of melioidosis in Malaysia is unknown and varies in different regions of the country, with reported hotspots associated with agriculture-related activities. To date, no incidence of human glanders has been reported in Malaysia, although occupational exposure for equine handlers and veterinary professionals remains a concern. Additionally, antibiotics are widely used in the healthcare and veterinary sectors to treat or prevent B. pseudomallei and B. mallei infections, leading to the emergence of resistance in B. pseudomallei. Lack of surveillance, research, assessment, and management of glanders and melioidosis is a major issue in Malaysia. Proper assessment systems and cross-discipline cooperation are vital to recognize and manage both diseases. Experts and practitioners from clinical and veterinary disciplines, environmentalists, law enforcement, policymakers, researchers, local communities, and other experts need to communicate, collaborate, and coordinate activities to fill the knowledge gap on glanders and melioidosis to reduce morbidity and mortality rates in the country. This review aims to define the organizational and functional characteristics of One Health surveillance approaches for glanders and melioidosis from a Malaysian perspective.

Sequencing-Based Genotyping of Pakistani Burkholderia mallei Strains: A Useful Way for Investigating Glanders Outbreaks

Burkholderia (B.) mallei is a host-adapted equine pathogen that causes glanders, a re-emerging zoonotic disease, which is endemic in Pakistan and other developing countries and seriously impacts the global equine movement. Due to globalization, the geographical restriction of diseases vanishes and the lack of awareness of and experience with eradicated diseases in industrialized countries also promotes the re-introduction of infections in these regions. Owing to the high equine population, the Pakistani province Punjab is a potential hotspot where several glanders outbreaks have been seen over last two decades. For determining the genomic diversity of B. mallei in this and other equine-populated prefectures, the genomes of 19 B. mallei strains isolated between 1999 and 2020 in different locations were sequenced and their genotypes were determined. Particularly, for genetically highly homogenous pathogens like B. mallei genotyping techniques require a high discriminatory power for enabling differentiation on the strain level. Thus, core-genome single nucleotide polymorphism (cgSNP) analysis was applied for distinguishing the highly similar strains. Furthermore, a whole-genome sequence-based core genome multi locus sequence typing (cgMLST) scheme, specific to B. mallei, was developed and additionally applied to the data. It was found that B. mallei genotypes in Pakistan persisted over time and space and genotype clusters preferred connection with a time point rather than the place of isolation, probably due to frequent equine movement, which promotes the spread of glanders. The cgMLST approach proved to work in accord with SNP typing and may help to investigate future glanders outbreaks.

Activation of Toll-Like Receptors by Live Gram-Negative Bacterial Pathogens Reveals Mitigation of TLR4 Responses and Activation of TLR5 by Flagella

Successful bacterial pathogens have evolved to avoid activating an innate immune system in the host that responds to the pathogen through distinct Toll-like receptors (TLRs). The general class of biochemical components that activate TLRs has been studied extensively, but less is known about how TLRs interact with the class of compounds that are still associated with the live pathogen. Accordingly, we examined the activation of surface assembled TLR 2, 4, and 5 with live Tier 1 Gram-negative pathogens that included Yersinia pestis (plague), Burkholderia mallei (glanders), Burkholderia pseudomallei (melioidosis), and Francisella tularensis (tularemia). We found that Y. pestis CO92 grown at 28°C activated TLR2 and TLR4, but at 37°C the pathogen activated primarily TLR2. Although B. mallei and B. pseudomallei are genetically related, the former microorganism activated predominately TLR4, while the latter activated predominately TLR2. The capsule of wild-type B. pseudomallei 1026b was found to mitigate the activation of TLR2 and TLR4 when compared to a capsule mutant. Live F. tularensis (Ft) Schu S4 did not activate TLR2 or 4, although the less virulent Ft LVS and F. novicida activated only TLR2. B. pseudomallei purified flagellin or flagella attached to the microorganism activated TLR5. Activation of TLR5 was abolished by an antibody to TLR5, or a mutation of fliC, or elimination of the pathogen by filtration. In conclusion, we have uncovered new properties of the Gram-negative pathogens, and their interaction with TLRs of the host. Further studies are needed to include other microorganism to extend our observations with their interaction with TLRs, and to the possibility of leading to new efforts in therapeutics against these pathogens.

Immunomodulatory Effect of Vitamin C on Proinflammatory Cytokines Production in Ossimi Lambs (Ovis aries) with Pneumonic Pasteurellosis

In this study, we have investigated the impact of vitamin C on the production of pro-inflammatory cytokines (interleukin 1 β (IL-1 β), interleukin 6 (IL-6), interleukin 12p40 (IL-12p40), interferon gamma (IFNγ), and tumor necrosis factor alpha (TNF-α)) in lambs naturally infected by pneumonic pasteurellosis. Of 37 lambs, 18 lambs were identified to have pneumonic pasteurellosis and randomly allocated into two equal groups. Single subcutaneous dose of tulathromycine alone (2.5 mg kg−1) or tulathromycine combined with vitamin C (3 gm kg−1) were administrated to the diseased lambs. The serum levels of IL-1β, IL-6, IFN-γ, and TNF-α were returned to the normal levels in pneumonic lambs treated with the combination therapy. The obtained results indicate the selective influences of vitamin C on pro-inflammatory cytokines production in sera of lambs with pneumonic pasteurellosis and highlights the value of vitamin C as a potential anti-inflammatory drug and ideal immunomodulatory agent.

Pathological and Immunohistochemical Analyses of Naturally Occurring Equine Glanders Using an Anti-BpaB Antibody

Glanders is caused by the gram-negative bacterium Burkholderia mallei. In this study, we investigated the histopathology and immunohistochemical localization of B. mallei in natural cases of equine glanders. Four horses showing clinical signs of nasal discharge and multiple cutaneous nodules or papulae in the hindlimbs and abdomen were reported in Mongolia. They tested positive for B. mallei infection on complement fixation, Rose Bengal agglutination, and mallein tests. Gross and histological lesions observed in these cases were similar to those previously reported in equine glanders. Immunohistochemistry using a monoclonal antibody to B. mallei BpaB showed localization of the bacterial antigen in the cytoplasm of neutrophils, macrophages, epithelioid cells, and multinucleated giant cells in the pyogranulomas and abscesses in target organs. Some alveolar type II cells and bronchiolar epithelial cells also contained the antigen. These results suggest that the anti-BpaB antibody is useful for identifying B. mallei-infected cell types in naturally infected horses.

Clinical repercussions of Glanders (Burkholderia mallei infection) in a Brazilian child: a case report

Glanders is a relatively unknown zoonotic disease caused by Burkholderia mallei. This bacterium affect solipeds and humans, and can be used as a biological warfare. Glanders is characterized as an occupational disease. We report the case of an 11-year-old boy who was presented to an emergency department with chest pain and dyspnea. He evolved into septic shock, pneumonia, and multiple abscesses. B. mallei was found in the exudate culture. Human infection is rare and difficult to confirm. The knowledge on glanders is important for differential diagnosis from other serious illnesses causing pneumonia and multiple abscesses.

The potential for an outbreak of glanders in Nepal

Confirmation of glanders has not been possible in suspected cases submitted by field veterinarians, mainly due to the lack of diagnostic tools in Nepal. In view, however, of the re-emergence of glanders in India and the unrestricted migration of equines from there in to Nepal, an outbreak of Glanders in the short term is a distinct possibility. Such an event would affect the rural, marginalized community, and brick kiln industries. Therefore, due attention on the national epidemiological study and strengthened animal quarantine system with holding yards and laboratory backups are highly requested. Besides, the government's timely action on disease prevalence, monitoring, and disease reporting is utmost important besides widespread public awareness to prevent the entry and control the disease.

[Assessment of the possibility of application in laboratory practice of reagent kit for diagnosis of glanders and melioidosis by real-time polymerase chain reaction.]

The reagent kit AmpligenBurk-mallei/pseudomallei-RT PCR is designed for detecting in vitro diagnostics and differentiate the DNA of glanders and melioidosis pathogens by real-time multiplex PCR in biological (clinical) material and cultures of microorganisms, as well as environmental objects and solid food products (rice). During clinical testing diagnostic value of reagent kit AmpligenBurk-mallei/pseudomallei-RT PCR has been studied. Based on the results obtained, a high analytical sensitivity (1×10³ microbe cells/ml) and specificity (100%) of PCR-RT with the developed reagent kit were established, regardless of the type of material being studied. The diagnostic sensitivity of PCR-RT using a set of reagents was at least 98.0% and specificity at least 99%. The stages of state examination have been completed, a registration certificate has been obtained at Roszdravnadzor, production, sale and use of reagent kit in medical laboratory practice have been permitted.

A novel selective medium for the isolation of Burkholderia mallei from equine specimens

BACKGROUND

Burkholderia mallei is a Gram-negative bacterium that causes glanders, a zoonotic disease, especially in equine populations (e.g. horses, donkeys, and mules). B. mallei usually grows slowly on most culture media, and this property makes it difficult to isolate from clinical specimens. One of the problems is that B. mallei is easily overgrown by other bacteria, especially in animal specimens collected from non-sterile sites. The aim of this study was to develop a new selective agar for the laboratory diagnosis of glanders. We formulated a new agar, named BM agar, to enrich B. mallei growth, but inhibit the growth of other bacteria and fungi based on their antimicrobial profiles. We compared the growth of B. mallei on BM with Xie's and PC agars, the two previously described selective agars for B. mallei.

RESULTS

BM agar could sufficiently grow almost all of the tested B. mallei strains within 72 h: only one out of the 38 strains grew scantly after 72 h of incubation. BM agar was further tested with other Burkholderia species and various bacterial species commonly found in the nasal cavities and on the skin of horses. We have found that other Burkholderia species including B. pseudomallei and B. thailandensis can grow on BM agar, but non-Burkholderia species cannot. Furthermore, the specificities of the three selective agars were tested with or without spiking B. mallei culture into clinical specimens of non-sterile sites collected from healthy horses. The results showed that BM agar inhibited growths of fungi and other bacterial species better than PC and Xie's agars. We have also found that growth of B. mallei on BM agar was equivalent to that on 5% horse blood agar and was significantly greater than those on the other two agars (P < 0.05).

CONCLUSIONS

We believe that BM agar can be used to efficiently isolate B. mallei from mixed samples such as those typically collected from horses and other contaminated environments.

MELIOIDOSIS AND GLANDERS: CURRENT STATE AND ACTUAL ISSUES OF EPIDEMIOLOGICAL SURVEILLANCE

Burkholderia pseudomallei and Burkholderia mallei are etiologic agents of glanders and melioidosis, the particularly dangerous infections of animals and humans, and are attributed to potential agents of bioterrorism. The manifestation of diseases ranges from acute septicemia to chronic infection, any organs and tissues are affected, andtreatment requires long intravenous and oral antibiotic courses. The endemic zone of glanders and melioidosis covers spacious regions in the world, and the number of imported cases to temperate regions is constantly increasing. For the Russian Federation, glanders and melioidosis are «forgotten» and «unknown» infections, and this review presents current data on their distribution in the world, epidemiological aspects, and laboratory diagnosis features.

Morphological Characteristics of Three Classic Forms of Natural Equine Glanders – A Disease With High Zoonotic Significance

Equine glanders is a severe bacterial disease known since ancient times. Although eradicated in the most part of the world it is now considered re-emerging. Considering very scarce literature data, we used from formalin fixed collection material: nasal septum, lung and skin specimens from naturally infected horses. Tissues were grossly examined and photographed. Tissue samples, after standard processing, were stained with HE, Congo red and Groccot and microscopically examined. Gross changes include nodules and ulcers in the nasal mucosa with granulation and scarring, pyogranulomas in the lung tissue and nodules and ulcers of the skin. Microscopically marked inflammation of affected tissues with neutrophilic and mononuclear infiltration and fibrous tissue proliferation were seen. As a potent zoonotic agent it has been already used as a biological weapon in the past.

Iron Acquisition Mechanisms and Their Role in the Virulence of Burkholderia Species

Burkholderia is a genus within the β-Proteobacteriaceae that contains at least 90 validly named species which can be found in a diverse range of environments. A number of pathogenic species occur within the genus. These include Burkholderia cenocepacia and Burkholderia multivorans, opportunistic pathogens that can infect the lungs of patients with cystic fibrosis, and are members of the Burkholderia cepacia complex (Bcc). Burkholderia pseudomallei is also an opportunistic pathogen, but in contrast to Bcc species it causes the tropical human disease melioidosis, while its close relative Burkholderia mallei is the causative agent of glanders in horses. For these pathogens to survive within a host and cause disease they must be able to acquire iron. This chemical element is essential for nearly all living organisms due to its important role in many enzymes and metabolic processes. In the mammalian host, the amount of accessible free iron is negligible due to the low solubility of the metal ion in its higher oxidation state and the tight binding of this element by host proteins such as ferritin and lactoferrin. As with other pathogenic bacteria, Burkholderia species have evolved an array of iron acquisition mechanisms with which to capture iron from the host environment. These mechanisms include the production and utilization of siderophores and the possession of a haem uptake system. Here, we summarize the known mechanisms of iron acquisition in pathogenic Burkholderia species and discuss the evidence for their importance in the context of virulence and the establishment of infection in the host. We have also carried out an extensive bioinformatic analysis to identify which siderophores are produced by each Burkholderia species that is pathogenic to humans.

Burkholderia mallei CLH001 Attenuated Vaccine Strain Is Immunogenic and Protects against Acute Respiratory Glanders

Burkholderia mallei is the causative agent of glanders, an incapacitating disease with high mortality rates in respiratory cases. Its endemicity and ineffective treatment options emphasize its public health threat and highlight the need for a vaccine. Live attenuated vaccines are considered the most viable vaccine strategy for Burkholderia, but single-gene-deletion mutants have not provided complete protection. In this study, we constructed the select-agent-excluded B. mallei ΔtonB Δhcp1 (CLH001) vaccine strain and investigated its ability to protect against acute respiratory glanders. Here we show that CLH001 is attenuated, safe, and effective at protecting against lethal B. mallei challenge. Intranasal administration of CLH001 to BALB/c and NOD SCID gamma (NSG) mice resulted in complete survival without detectable colonization or abnormal organ histopathology. Additionally, BALB/c mice intranasally immunized with CLH001 in a prime/boost regimen were fully protected against lethal challenge with the B. mallei lux (CSM001) wild-type strain.

Genotyping of Burkholderia mallei from an outbreak of glanders in Bahrain suggests multiple introduction events

Background

Glanders, caused by the gram-negative bacterium Burkholderia mallei, is a highly infectious zoonotic disease of solipeds causing severe disease in animals and men. Although eradicated from many Western countries, it recently emerged in Asia, the Middle-East, Africa, and South America. Due to its rareness, little is known about outbreak dynamics of the disease and its epidemiology.

Methodology/Principal Findings

We investigated a recent outbreak of glanders in Bahrain by applying high resolution genotyping (multiple locus variable number of tandem repeats, MLVA) and comparative whole genome sequencing to B. mallei isolated from infected horses and a camel. These results were compared to samples obtained from an outbreak in the United Arab Emirates in 2004, and further placed into a broader phylogeographic context based on previously published B. mallei data. The samples from the outbreak in Bahrain separated into two distinct clusters, suggesting a complex epidemiological background and evidence for the involvement of multiple B. mallei strains. Additionally, the samples from Bahrain were more closely related to B. mallei isolated from horses in the United Arab Emirates in 2004 than other B. mallei which is suggestive of repeated importation to the region from similar geographic sources.

Conclusion/Significance

High-resolution genotyping and comparative whole genome analysis revealed the same phylogenetic patterns among our samples. The close relationship of the Dubai/UAE B. mallei populations to each other may be indicative of a similar geographic origin that has yet to be identified for the infecting strains. The recent emergence of glanders in combination with worldwide horse trading might pose a new risk for human infections.

Glanders is a disease of antiquity, recognized as a malady of equines by Hippocrates and Aristotle. The causative agent, Burkholderia mallei, is currently feared as a potential biological weapon and has been used as such in the American Civil War and both World Wars to cripple equine military components. In the more economically developed countries, glanders has been eradicated through large scale culling. As a result, our understanding of transmission dynamics and networks is limited. However, regions of endemicity still exist in Asia, the Middle-East, Africa, and South America where it infects solipeds and camels. These areas provide reservoirs for re-introduction of glanders into countries previously listed as glanders-free. Here, we demonstrate the utility of high-resolution genotyping and whole genome sequence analysis in the investigation of a recent outbreak of glanders in horses and camels in Bahrain, a previously declared glanders-free country. Our analyses demonstrate that not one, but two strains likely caused this outbreak, and that these strains probably came from a similar geographic region via importation of infected animals. Even with careful monitoring, the global trade of animals from glanders-endemic regions can re-introduce and possibly re-establish this disease in animal populations of countries that have previously eradicated it.