Isolation of Burkholderia pseudomallei from a goat in New Caledonia: implications for animal and human health monitoring and serological tool comparison

BACKGROUND

Melioidosis is a serious bacterial infection caused by Burkholderia pseudomallei, a gram-negative bacterium commonly found in soil and water. It can affect both humans and animals, and is endemic in regions such as Southeast Asia and Northern Australia. In recent years, there have been reports of an emergence of human melioidosis in other areas, including New Caledonia.

RESULTS

During standard laboratory analysis in New Caledonia in 2021, a strain of B. pseudomallei was isolated from a goat. The strain was characterized using both MLST and WGS techniques and was found to cluster with previously described local human strains from the area. In parallel, several serological tests (CFT, ELISA, Luminex (Hcp1, GroEL, BPSS1840), arrays assay and a latex agglutination test) were performed on animals from the farm where the goat originated, and/or from three other neighboring farms. Using two commercial ELISA kits, seropositive animals were found only on the farm where the infected goat originated and tests based on recombinant proteins confirmed the usefulness of the Hcp1 protein for the diagnosis of melioidosis in animals.

CONCLUSIONS

Despite the regular reports of human cases, this is the first confirmed case of melioidosis in an animal in New Caledonia. These results confirm the presence of the bacterium in the region and highlight the importance of vigilance for both animal and human health. It is critical that all health partners, including breeders, veterinarians, and biologists, work together to monitor and prevent the spread of the disease.

Molecular characterization of Burkholderia mallei strains isolated from horses in Brazil (2014-2017)

Glanders is an infectious zoonosis caused by Burkholderia (B.) mallei that mainly affects equids. The objective of this work was to provide additional knowledge on the diversity of the strains circulating in Brazil. Six Burkholderia mallei isolates obtained during necropsies of glanderous horses between 2014 and 2017 in two different states (Pernambuco and Alagoas) were analyzed by polymerase chain reaction-high-resolution melting (PCR-HRM). While four strains (9902 RSC, BM_campo 1, BM_campo 3 and UFAL2) clustered in the L3B2 branch, which already includes the Brazilian 16-2438_BM#8 strain, two strains (BM_campo 2.1 and BM_campo 2.2) clustered within the L3B3sB3 branch, which mostly includes older isolates, from Europe and the Middle East. Whole genome sequencing of two of these strains (UFAL2 and BM_campo 2.1), belonging to different branches, confirmed the HRM typing results and refined the links between the strains, including the description of the L3B3Sb3Gp1SbGp1 genotype, never reported so far for contemporary strains. These results suggest different glanders introduction events in Brazil, including a potential link with strains of European origin, related to colonization or trade.

Molecular epidemiology of Burkholderia mallei isolates from India (2015-2016): New SNP markers for strain tracing

Glanders, caused by a bacterium called B. mallei, is primarily an infectious horse and human disease. Although its incidence is rare in developed countries, it is nonetheless prevalent in several geographical areas of the world. There is a lack of cost-effective, rapid and specific molecular typing tools for epidemiological tracing of glanders cases. We previously reported an SNP-based typing method that categorizes global B. mallei strains into three lineages (L1 to L3), as well as additional branches, sub-branches and groups. However, further discrimination of the Indian and Pakistani isolates within the L2B2sB2 sub-branch was not possible due to the lack of sufficient epidemiological markers. In this study, 10 B. mallei strains isolated from four states in India during 2015-2016 were whole genome sequenced; SNP analysis further confirmed their position in the L2B2sB2 branch. To better track the strains, four new markers targeting Indian or Pakistani strains, and specifically targeting sub-groups within the Indian strains, were identified. The new SNP markers were tested and validated on the 10 Indian isolates included in this study as well as on 6 contemporary B. mallei Pakistani strains. These rapid and discriminating typing tools will contribute to the epidemiological monitoring of B. mallei infections, particularly in South Asia and the Middle East, endemic regions of the disease.

A genetic variant of Burkholderia mallei detected in Kuwait: Consequences for the PCR diagnosis of glanders

Glanders is a contagious zoonotic disease caused by Burkholderia mallei. Following the detection of glanders positive horses using the OIE complement fixation test, the tissues of two horses were analysed by PCR. While PCR systems targeting the Burkholderia pseudomallei complex gave positive signals, the species-specific PCR systems targeting B. mallei (fliP-IS407A) and B. pseudomallei (orf11)-the OIE recommended targets-resulted in negative signals. However, the presence of B. mallei in these tissues was confirmed with a recently described B. mallei-specific real-time PCR system and genotyping with MLST- and SNP-based methods, performed on the most positive tissue, identified a genotype closely related to B. mallei strains recently isolated in the Middle East. This study leads to recommendations regarding the use of PCR systems for the molecular diagnosis of glanders, especially in regions where the circulating B. mallei strains have not yet been fully genetically characterized.

Development of a microsphere-based immunoassay for the serological detection of glanders in equids

Burkholderia mallei is the etiologic agent of glanders, an infectious disease of solipeds, with renewed scientific interest due to its increasing incidence in different parts of the world. More rapid, sensitive and specific assays are required by laboratories for confirmatory testing of this disease. A microsphere-based immunoassay consisting of beads coated with B. mallei recombinant proteins (BimA, GroEL, Hcp1, and TssB) has been developed for the serological diagnosis of glanders. The proteins' performance was compared with the OIE reference complement fixation test (CFT) and an indirect enzyme-linked immunosorbent assay (iELISA) on a large panel of sera comprised of uninfected horses (n=198) and clinically confirmed cases of glanders from India and Pakistan (n=99). Using Receiver Operating Characteristics (ROC) analysis and adjusting the cutoff levels, Hcp1 (Se=100%, Sp=99.5%) and GroEL (Se= 97%, Sp=99.5%) antigens exhibited the best specificity and sensitivity. Neither Hcp1 and GroEL proteins, nor iELISA reacted with doubtful and positive CFT samples from glanders free countries which further confirmed the false positive reactions seen in CFT.