# Diagnosis and genotyping of melioidosis in a domestic cat in New Caledonia

Karine Laroucau, Audrey Stefanini, Bernice Klotoe, Jules Terret, Fabien Vorimore, Sophie A. Granier, Julien Colot, Megane Gasque, Bart J. Currie, Anais Desoutter

► To cite this version:

Karine Laroucau, Audrey Stefanini, Bernice Klotoe, Jules Terret, Fabien Vorimore, et al. Diagnosis and genotyping of melioidosis in a domestic cat in New Caledonia. Veterinary Microbiology, 2025, 310, pp.110739. 10.1016/j.vetmic.2025.110739. anses-05395328

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# Diagnosis and genotyping of melioidosis in a domestic cat in New Caledonia

K. Laroucau<sup>a,*</sup>, A. Stefanini<sup>b</sup>, B. Klotoe<sup>a</sup>, J. Terret<sup>a</sup>, F. Vorimore<sup>c</sup>, S.A. Granier<sup>d</sup>, J. Colot<sup>e</sup>, M. Gasque<sup>a</sup>, B.J. Currie<sup>f,g</sup>, A. Desoutter<sup>h</sup>

## ARTICLE INFO

**Keywords:**

Melioidosis

*Burkholderia pseudomallei*

Genotyping

Serology

ELISA

Companion animals

## ABSTRACT

**Objectives:** To report a case of melioidosis in a domestic cat in New Caledonia, describing the diagnostic, microbiological and molecular findings. To evaluate the potential of a glanders serological test for assessing exposure to *Burkholderia pseudomallei*.

**Methods:** A domestic cat presenting with respiratory symptoms underwent clinical and radiographic examination. Bacterial culture was performed on bronchoalveolar lavage fluid, and the strain was characterised using MALDI-TOF mass spectrometry and whole-genome sequencing. In silico multi-locus sequence typing (MLST) and phylogenetic analyses were also conducted. Serology was assessed using a commercial ELISA (GLANDA ELISA, IDVet), which was originally developed for diagnosing glanders.

**Results:** *Burkholderia pseudomallei* was isolated and sequenced, revealing ST2147, which has been previously identified in New Caledonia. Phylogenetic analysis confirmed clustering with strains from the Pacific region. The cat's serum tested strongly positive by ELISA, suggesting the potential of this test for assessing exposure to *B. pseudomallei* in cats and other animals. Screening of archived feline sera identified only one additional seropositive cat, suggesting low prevalence.

**Conclusions:** This case supports the presence of multiple *B. pseudomallei* genotypes in New Caledonia and highlights the risk of melioidosis in cats. The commercial GLANDA ELISA shows promise as a tool for demonstrating animal exposure to *B. pseudomallei*, directing the need for culturing for confirmation of melioidosis. Enhanced awareness among veterinarians is essential for the early diagnosis and management of this disease in companion animals.

## 1. Introduction

Melioidosis is caused by the bacterium *Burkholderia (B.) pseudomallei*, which is found in the environment and can infect both humans and animals (Wiersinga et al., 2018). This saprophyte, which lives in soil and water, is endemic to Southeast Asia and northern Australia, but is increasingly being reported in the Pacific, Africa, and the Americas

(Warner and Currie, 2018). Human cases are regularly reported in New Caledonia (Le Hello et al., 2005; Melot et al., 2016), and the first case in an animal was recently documented in a goat (Desoutter et al., 2024).

Although primarily a human health concern, melioidosis also affects domestic and wild animals, highlighting its importance in veterinary medicine. Different species of animal have varying levels of susceptibility to the disease. For example, sheep and goats are highly

<footnote><sup>a</sup> Anses, Animal Health Laboratory, Bacterial Zoonosis Unit, Maisons-Alfort, France</footnote>

<footnote><sup>b</sup> Veterinary Clinic, La Foa, New Caledonia</footnote>

<footnote><sup>c</sup> Anses, Identypath, Maisons-Alfort, France</footnote>

<footnote><sup>d</sup> Anses, Strategy and Programs Department, Research and Reference Division, Maisons-Alfort, France</footnote>

<footnote><sup>e</sup> Territorial Hospital Center Gaston-Bourret, Medical Biology Laboratory, Noumea, New Caledonia</footnote>

<footnote><sup>f</sup> Royal Darwin Hospital, Darwin, Australia</footnote>

<footnote><sup>g</sup> Global and Tropical Health Division, Menzies School of Health Research, Charles Darwin University, Darwin, Australia</footnote>

<footnote><sup>h</sup> LNC (Laboratory of New Caledonia), Animal Health Department, Païta, New Caledonia</footnote>

<footnote>* Corresponding author.</footnote>

<footnote>E-mail addresses: karine.laroucau@anses.fr (K. Laroucau), audreystefanini@hotmail.fr (A. Stefanini), Bernice.klotoe@anses.fr (B. Klotoe), Jules.terret@anses.fr (J. Terret), fabien.vorimore@anses.fr (F. Vorimore), sophie.granier@anses.fr (S.A. Granier), Julien.Colot@cht.nc (J. Colot), Megane.gasque@anses.f (M. Gasque), Bart.Currie@menzies.edu.au (B.J. Currie), anais.desoutter@gouv.nc (A. Desoutter).</footnote>
susceptible, while cats, dogs, and cattle are relatively resistant (Parkes et al., 2009).

Cats can acquire *B. pseudomallei* through skin inoculation, by ingesting contaminated material, or by inhaling aerosolised bacteria. Clinical presentations can range from localised abscesses and ocular signs to disseminated infections (Chooi, 1986; O'Brien et al., 2003; Parkes et al., 2009). Common symptoms include lethargy, jaundice, and neurological deficits such as limb paralysis. As with human cases, there is often severe systemic deterioration. Histopathology in fatal cases often reveals abscesses in the liver, spleen, and lymph nodes, as well as purulent bronchopneumonia. The disease typically progresses rapidly, and without prompt intervention, affected cats may die within days, even with antimicrobial treatment (O'Brien et al., 2003; Parkes et al., 2009). Co-infection with other pathogens, such as *Bartonella henselae* (as reported in a Malaysian case (Azri and Ismail, 2022)), may further complicate the clinical course.

Despite its severity, feline melioidosis is likely to be under-reported due to diagnostic challenges. The non-specific nature of the clinical signs, coupled with reliance on specialised techniques such as isolating and correctly identifying *B. pseudomallei* in biological samples, contributes to under-reporting. A definitive diagnosis requires culture of *B. pseudomallei* from samples such as blood, pus or tissue biopsies (Wiersinga et al., 2018). Treatment involves prolonged antibiotic therapy. For acute human cases, treatment initially involves ceftazidime (a third-generation cephalosporin) or a carbapenem such as meropenem or imipenem, followed by trimethoprim-sulfamethoxazole to eradicate the infection (Wiersinga et al., 2018). However, treatment in animals is considered costly and often unsuccessful (Narayanan, 2022).

## 2. Case description

On 12 April 2022, a 1.5-year-old neutered female cat from Foa, New Caledonia, was presented with anorexia and a persistent fever of 40 °C. Despite the fever, a physical examination revealed no abnormalities such as conjunctivitis or significant weight loss. Haematology showed a normal white blood cell count (WBC = 10,000) (Table S1), and an abdominal ultrasound scan revealed no abnormalities despite impaired bowel transit.

The cat tested negative for feline immunodeficiency virus (FIV), and there was no history of fighting with other cats. Initial supportive care involving the administration of meloxicam (0.2 mg/kg subcutaneously on day one, followed by 0.1 mg/kg per day for two days) was provided to control the fever.

As no improvement was observed and a pulmonary abnormality was detected, treatment was initiated with amoxicillin/clavulanic acid (12.5 mg/kg twice daily for eight days) and buprenorphine (10 µg/kg twice daily intravenously) to control the infection, provide analgesia and maintain hydration. Although this regimen resulted in an improved appetite; a low-grade fever (39.5 °C) persisted.

On 21 April, auscultation revealed mild rhonchi and increased breath sounds. Chest radiographs confirmed bronchopneumonia (Fig. 1). Treatment was amended to include cephalexin (15 mg/kg twice daily) for antibacterial therapy and prednisolone (0.5 mg/kg per day) to reduce pulmonary inflammation and a deworming protocol targeting pulmonary parasites (esafoxolaner/eprinomectin/praziquantel). The first-line antibiotics typically used to treat bronchopneumonia in companion animals typically include amoxicillin/clavulanic acid, cephalexin and trimethoprim-sulfonamides. However, trimethoprim-sulfonamides tablets are difficult to administer to cats. In New Caledonia, failures with amoxicillin/clavulanic acid due to resistance are common, whereas cephalexin tend to be better tolerated.

Nevertheless, no improvement was observed after one week. Bronchoalveolar lavage (BAL) was then performed for bacteriological analysis, resulting in the isolation of *B. pseudomallei*. The bacterium was identified using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (Microflex, Bruker), alongside

<figure><img src="image_3.png" /><figcaption>**Fig. 1.** Lateral (1) and dorsal thoracoabdominal (2) radiographs of the cat taken on 12 April 2022, showing generalised bronchial opacities (a) and caudodorsal alveolar opacities (b).</figcaption></figure>

the MBT Compass SR taxonomy database.

The cat's condition remained stable, although it had intermittent fever. However, it was euthanised shortly afterwards because of perception of a potential zoonotic hazard posed by *B. pseudomallei*. As there were no BSL-3 facilities in New Caledonia in which to perform an animal necropsy, only blood samples were collected.

The strain isolated from the cat and designated strain 22-9817/5 was characterised using whole genome sequencing as previously described (Klotoe et al., 2025; ENA accession number GCA_965201125). In silico multi-locus sequence typing (MLST) assigned the strain to sequence type (ST)2147 via the *B. pseudomallei* PubMLST database (https://pubmlst.org/). This ST has also been reported from recent isolates obtained from a Caledonian patient.

A phylogenetic tree constructed using the concatenated sequences of seven housekeeping genes for MLST revealed that the New Caledonian strains grouped with those from the Pacific region (Fig. 2). A more refined analysis, based on unique single-nucleotide polymorphisms (SNPs) extracted from whole-genome sequences, revealed that three previously sequenced New Caledonian strains (one from a goat in 2021 and two from humans) formed a distinct cluster, whereas the cat strain 22-9817/5 belonged to a separate branch. These results imply the existence of various environmental reservoirs of *B. pseudomallei* in New Caledonia and confirm that it is endemic in that Pacific nation. However, the origins of *B. pseudomallei* in New Caledonia and how widespread these bacteria are dispersed across the islands remain to be determined.

This young, neutered, FIV-negative cat lived with more than a dozen other cats, including strays, and is very likely to have been exposed to *B. pseudomallei* in the environment. The cat had access to almost one hectare of outdoor land in the bush, but no host-related predisposing factors were identified. However, the climatic conditions during the year of infection were unusual: a particularly rainy season characterised by repeated depressions and influenced by La Niña resulted in exceptional
<figure><img src="image_4.png" /><figcaption>**Fig. 2.** Phylogeny of selected *Burkholderia pseudomallei* strains. (A) The MLST phylogeny was constructed using the maximum likelihood method and the Kimura 2-parameter model in MEGA X, with sequence types (STs) selected based on the study by Melot et al. (2016). (B) The SNP phylogeny was constructed using the core genome alignment, including both variant and invariant sites, with the neighbour-joining method and the Tamura-Nei model in Geneious Prime. The genomes of the isolates used in the MLST tree were obtained from the PubMLST website and used to construct the SNP phylogeny. The PhaME pipeline identified 118,941 SNP positions from a total core genome length of 6,013,458 bp. Strains from New Caledonia are marked with blue stars and the strain isolated from the cat in this study (22-9817_5) is indicated by a red arrow.</figcaption></figure>

rainfall in the region where the cat lived, which is normally drier. Notably, another cat from the same household had a history of recurrent abscesses and renal failure, which was suspected to be associated with renal lymphoma. A third cat had experienced a febrile episode six months earlier that had resolved following treatment, although no specific details were provided. Neither of these co-habiting cats was tested specifically for melioidosis.

Antimicrobial susceptibility testing was performed on the *B. pseudomallei* isolate from the cat using the European Committee on Antimicrobial Susceptibility Testing disc diffusion methodology and interpretations (EUCAST, 2025; Dance et al., 2021). The isolate had a standard susceptibility profile as seen in primary melioidosis cases, although the zone diameter was on the breakpoint for meropenem and at the lower end of the standard range for trimethoprim-sulfamethoxazole (Table S2).

The cat serum was tested using the GLANDA ELISA test (IDVet, France). This is a commercial diagnostic test that was originally developed for equine glanders, caused by *B. pseudomallei*, but which has also previously been shown to effectively detect exposure to *B. pseudomallei*. The test has been successfully used on a goat herd with a confirmed case of melioidosis in New Caledonia in 2021 (Desoutter et al., 2024), and more recently on a Caribbean Island (Gasqué et al., 2024). The test detected a high antibody level (S/P value > 370 %) in this cat. These findings suggest that the test could be useful for demonstrating animal exposure to *B. pseudomallei*, alerting to and directing the need for culturing for confirmation of melioidosis. Screening of archived feline sera from New Caledonia (n = 140; 2016–2025) using the GLANDA ELISA identified an additional cat with exposure to *B. pseudomallei* (two

samples from the same cat sampled twice in 2018; Table S3). This indicates a low prevalence in this cohort and supports the specificity of the test. However, the possibility of limited sensitivity cannot be ruled out, especially in acute, early melioidosis disease and further studies involving confirmed cases are needed to assess the test's performance more accurately. Unfortunately, no further information is available regarding the seropositive cat from 2018.

### 3. Conclusion

Although human cases are well documented (Le Hello et al., 2005; Melot et al., 2016), this report describes the first confirmed case of melioidosis in a cat in New Caledonia. This follows the first reported case of melioidosis in a goat in the territory (Desoutter et al., 2024). This case highlights the importance of including melioidosis in the differential diagnosis of companion animals in endemic regions. The cat presented with a pulmonary infection, which is consistent with previously reported cases in other species of animal and in humans (Sprague and Neubauer, 2004; Wiersinga et al., 2018). Diagnostic investigations should include bacteriological cultures of bronchoalveolar lavage fluid and blood cultures in cases of sepsis or disseminated disease, as well as swabs of abscesses. Serological testing using the GLANDA ELISA shows promise for supporting a diagnosis of the disease in cats, although further evaluation using additional clinical cases is required to determine its diagnostic performance and broader applicability across species. It is important to emphasise that serology can reflect past exposure and culture of *B. pseudomallei* is required to confirm melioidosis.

Since 2010, the Darwin Royal Hospital has recommended the
following treatment protocol for humans consisting of an initial intra-
venous phase of ceftazidime or meropenem for at least 14 days, followed
by an oral eradication phase of trimethoprim-sulfamethoxazole for at
least three months (Currie, 2014; www.melioidosis.info). There is little
therapeutic guidance available for cats. Treatment should be guided by
antimicrobial susceptibility testing, with the dosage carefully adjusted
to take feline physiology into account. The need for prolonged treat-
ment, the guarded prognosis, and the biosafety precautions required due
to the considered but in reality low zoonotic risk to owners, veterinar-
ians and laboratory staff must also be acknowledged. We acknowledge
that the initial management of this cat was suboptimal for sepsis and
that specific therapy for melioidosis was not able to be given once the
diagnosis was made. This case highlights the need to raise awareness of
melioidosis among veterinarians working in endemic regions such as
New Caledonia. Early recognition, diagnosis and treatment are crucial in
minimising the risk to animal and human health.

CRediT authorship contribution statement

**Karine Laroucau:** Writing – review & editing, Writing – original draft, Funding acquisition, Formal analysis, Conceptualization. **Audrey Stefanini:** Writing – review & editing, Investigation. **Bernice Klotoe:** Writing – review & editing, Methodology. **Jules Terret:** Writing – review & editing, Methodology. **Fabien Vorimore:** Writing – review & editing, Methodology. **Sophie Granier:** Writing – review & editing, Validation. **Julien Colot:** Writing – review & editing, Methodology. **Mégane Gasque:** Writing – review & editing, Methodology. **Bart J Currie:** Writing – review & editing. **Anais Desoutter:** Writing – review & editing, Methodology, Investigation.

Funding statement

This work was funded through the internal resources of Anses and LNC.

Declaration of Competing Interest

None of the authors have any financial or personal relationships with any individuals or organizations that could inappropriately influence or bias this paper.

Acknowledgments

We would like to thank the microbiology and serology technicians at
the Laboratory of New Caledonia (LNC) for their technical support and
commitment throughout this study. We are grateful to the reviewers for
their constructive comments.

**Appendix A. Supporting information**

Supplementary data associated with this article can be found in the
online version at doi:10.1016/j.vetmic.2025.110739.

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