Abstract
Background:
Canine tuberculosis caused by Mycobacterium tuberculosis is rare and often underdiagnosed. This case report aims to describe the clinical, pathological, and molecular features of a dog with systemic tuberculosis, highlighting its epidemiological relevance within a One Health framework. The specific objective is to characterise a confirmed case of systemic M. tuberculosis infection in a dog, emphasising its unique clinicopathological features, including hypercalcaemia, and documenting an inferred reverse zoonotic transmission with subsequent intra-household zoonotic re-exposure.
Methods:
A 4-year-old male American Staffordshire terrier presented with lethargy, acute vomiting, anorexia, weight loss, generalised muscle atrophy, ataxia, and a history of chronic cough, orthopaedic disease, and dermatopathy treated with corticosteroids. Clinical evaluation revealed hypercalcaemia, oxaluria, proteinuria, and chronic respiratory and dermatological signs. Cytology showed granulomatous inflammation with intracytoplasmic negatively staining bacilli, raising suspicion for mycobacterial infection. Due to clinical deterioration, euthanasia was performed. Gross and histopathology revealed disseminated granulomatous hepatitis, nephritis, prostatitis, splenitis, and pneumonia with extensive caseous necrosis and mineralization. Ziehl–Neelsen staining confirmed intralesional acid-fast bacilli. Molecular diagnostics (PCR/RFLP, cgMLST) identified Mycobacterium tuberculosis complex (MTBC), and whole-genome sequencing revealed drug-susceptible M. tuberculosis lineage 4.1.2.1 (Haarlem), unrelated to other local strains. Epidemiological investigation supported reverse zoonotic transmission from an infected owner, with possible secondary transmission to a cohabiting individual.
Conclusion:
This case provides a detailed description of systemic canine tuberculosis and highlights hypercalcaemia as a potentially useful clinicopathological clue in veterinary patients with systemic granulomatous disease due to M. tuberculosis. The evidence supports a reverse zoonotic transmission of M. tuberculosis from human to dog, followed by onward zoonotic transmission to a cohabiting person who developed latent infection. This case underscores the importance of integrated cross-species epidemiological surveillance and the need to strengthen diagnostic and tracing protocols for companion animals within a One Health perspective.
1 Introduction
Canine infection with Mycobacterium tuberculosis (MTB) is a rare but increasingly recognised condition with significant zoonotic implications. Transmission from humans to dogs has been documented in both domestic and stray populations, often in households or environments with active human tuberculosis (1–4). Clinical presentations in dogs are variable, ranging from enteric and intra-abdominal forms (1, 5, 6) to pulmonary (4, 7) and cutaneous manifestations (8). Recent reviews have highlighted the growing number of confirmed cases and the diagnostic challenges they pose (9–11). Dogs may serve as sentinels or silent reservoirs in high-risk settings, particularly in rural or livestock-associated environments (12). The zoonotic risk is underscored by reports of occupational exposure among veterinary personnel during necropsy procedures (13).
Several previous reports have described hypercalcaemia (total and/or ionised) associated with infectious or parasitic granulomatous diseases in dogs, including angiostrongylosis, idiopathic granulomatous lymphadenitis, blastomycosis, and schistosomiasis (e.g., infection with Heterobilharzia Americana) (14–21). In this report, we describe a case of Mycobacterium tuberculosis infection in an owned dog, in which we highlight hypercalcaemia as a potentially significant clinicopathological finding in dogs with systemic granulomatous disease caused by M. tuberculosis.
Whilst hypercalcaemia is sporadically reported in canine tuberculosis (9, 22), it is a recognised paraneoplastic and granulomatous marker in human patients with pulmonary and extrapulmonary TB (23–26). The underlying mechanism is thought to involve macrophage-mediated extra renal synthesis of calcitriol, leading to increased intestinal calcium absorption (27, 28). Cases of hypervitaminosis D and hypercalcaemic crisis have been described in people with MTB infection across age groups and organ systems (29–31).
To our knowledge, this case represents another sporadic report of hypercalcaemia associated with disseminated MTB infection in a dog, suggesting a potentially relevant diagnostic parameter for systemic granulomatous inflammation that warrants further investigation in veterinary medicine. It further highlights the importance of integrated surveillance and collaboration between veterinary and human medicine, reinforcing the One Health approach to infectious disease management across species.
2 Case history
A 4-year-old intact male American Staffordshire terrier, weighing 24.5 kg, presented to the Veterinary Clinic and Laboratory San Marco with a 5-day history of acute vomiting, anorexia, lethargy, and progressive weight loss. The dog was fed a commercial dry diet and lived both indoors and outdoors. Vaccination history was incomplete and not compliant with the vaccination guidelines (32). The dog had a history of chronic dermatitis, intermittent coughing, and a past allergic reaction. Previously, he underwent surgical repair for cranial cruciate ligament rupture. Multiple courses of corticosteroids (prednisolone) had been administered over time for dermatological and orthopaedic conditions.
3 Clinical findings
On clinical examination, the dog was depressed, ataxic, and showed generalised muscle atrophy. Mucous membranes were pale to sub-icteric. Neurological assessment revealed proprioceptive deficits in all four limbs. His body condition score was assessed to be 1/5, consistent with an emaciated state.
Initial diagnostic tests revealed moderate metabolic acidosis, moderate to severe anaemia, and thrombocytosis. A mild elevation in coagulation parameters was also observed. The serum sample was icteric and haemolytic. Protein electrophoresis reported an inflammatory pattern with α2 and γ-globulin peaks (Figure 1).
Figure 1
Biochemistry described a picture of severe inflammatory status along with kidney and liver failure. Notably, hypercalcaemia (12.9 mg/dL; reference range 9.8–10.9) and hyperphosphataemia (6.8 mg/dL; 2.8–3.9) were observed, with an increased calcium-phosphate product (Ca × p = 85.7 mg2/dL2; reference range 20–46.6), as shown in Table 1. Blood gas analysis confirmed the hypercalcaemia (1.68 mmol/L; reference range 1.29–1.40), while serum parathyroid hormone (PTH) was below the reference range (1.4–16.2 pg./mL).
Table 1
| Parameter | Result | Reference range |
|---|---|---|
| RBC | 4.43 ×106 | 7.1–8.22 |
| Reticulocytes (/μL) | 111,961 | 9,975–42,893 |
| WBC | 11.09 ×103 | 6.52–11.67 |
| Platelets | 441 ×103 | 157–329 |
| CRP | 2.66 mg/dL | 0.01–0.03 |
| Haptoglobin | 524 mg/dL | 33–92 |
| Ferritin | 612 ng/mL | 59–168 |
| CK | 914 IU/L | 59–164 |
| AST | 209 IU/L | 22–41 |
| ALT | 183 IU/L | 34–177 |
| ALP | 1,497 IU/L | 16–38 |
| GGT | 10.9 IU/L | 2.1–5.4 |
| LDH | 447 IU/L | 10–110 |
| Total bilirubin | 3.52 mg/dL | 0.13–0.26 |
| Albumin | 2.1 g/dL | 3.1–3.7 |
| Globulins | 6.5 g/dL | 2.8–3.4 |
| A/G ratio | 0.32 | 0.97–1.24 |
| Triglycerides | 136 mg/dL | 25–65 |
| Cholesterol | 384 mg/dL | 147–253 |
| Urea | 193 mg/dL | 30–43 |
| Creatinine | 2.56 mg/dL | 0.9–1.39 |
| Calcium | 12.9 mg/dL | 9.8–10.9 |
| Phosphorus | 6.8 mg/dL | 2.8–3.9 |
| Ca × P product | 85.7 mg/dL | 20–46.6 |
| aPTT | 15.6 s | 10.4–12.3 |
| PT | 9.9 s | 7.4–8.35 |
| Fibrinogen | 303 mg/dL | 149–223 |
Selected laboratory findings (abnormal results only) for the dog at the time of admission.
RBC, Red Blood Cells; WBC, White Blood Cells; aPTT, Activated Partial Thromboplastin Time; PT, Prothrombin Time; CRP, C-Reactive Protein; CK, Creatine Kinase; AST, Aspartate Aminotransferase; ALT, Alanine Aminotransferase; ALP, Alkaline Phosphatase; GGT, Gamma-Glutamyl Transferase; LDH, Lactate Dehydrogenase; A/G ratio, Albumin/Globulin ratio.
Due to the complex hepatic and renal profile, additional serological investigations were performed to rule out potential infectious or parasitic comorbidities. Particularly, serological analysis using the microscopic agglutination test (MAT) for anti-Leptospira (L.) spp. antibodies revealed positive titres for L. Grippotyphosa var. Grippotyphosa (1:100) and L. icterohaemorrhagiae var. Copenhageni (1:800). Considering the diagnostic threshold of ≥1:100, as established by the World Organisation of Animal Health (WOAH) (2023) (33), the result indicates exposure to Leptospira spp. Quantitative ELISA for antibodies against Leishmania infantum was negative.
Hyposthenuria (SG 1.015), haematuria, proteinuria; PU/CU ratio 7.2 (ref: 0.1–0.3); calcium oxalate dihydrate crystals; urinary creatinine 19.6 (ref: 0.0–3.2) have been reported from the urinalysis.
Thoracic radiographs obtained in standard projections (right and left lateral recumbency and ventrodorsal view) revealed a diffuse nodular interstitial pulmonary pattern characterised by increased parenchymal opacity, reduced vascular definition, and bilateral reticulonodular infiltrates. Pleural thickening and mediastinal widening were also noted, suggestive of concurrent pleural effusion/lymphadenopathy.
Abdominal ultrasound (US) showed bilateral nephromegaly with parenchymal disorganisation, multiple confluent hypoechoic lesions, intralesional micromineralizations, and subcortical hypoechoic halo in both kidneys. Furthermore, hepatomegaly with diffusely hypoechoic parenchyma and millimetric intraparenchymal and ductal mineralisations have been described on liver US (Figures 2a,b).
Figure 2
Fine-needle aspiration (FNA) and cytological examination from the liver and kidney revealed macrophagic-neutrophilic inflammation with intracytoplasmic negatively staining rod-shaped structures within the macrophages (Figure 3).
Figure 3
Despite intensive supportive care, the dog’s condition rapidly deteriorated, progressing to multi-organ dysfunction and showing additional abnormalities such as worsening azotaemia, marked electrolyte imbalances, and increasing hepatic enzyme activities. Euthanasia was elected due to the poor prognosis.
4 Gross pathology
At necropsy, generalised soft tissue pallor, mucous membrane sub-icterus, and skeletal muscle atrophy were observed. The skeletal musculature appeared diffusely pale and decreased in volume.
Mild bicavitary dark red effusions were present. The lungs were diffusely congested and oedematous, associated with a small amount of foam in the lumen of the deep airways. Multiple small, disseminated nodules were also visible throughout the pulmonary parenchyma.
The gastric mucosa exhibited multifocal necrotic and erosive lesions, with traces of digested blood within the gastric contents. The intestinal lumen throughout the tract contained catarrhal and dark, tarry material. The liver was enlarged, pale yellow with numerous miliary white nodules, exhibiting a firm, calcified texture upon sectioning. The spleen was enlarged and mildly pale. The kidneys were severely enlarged, irregular, and partially calcified upon sectioning. The renal parenchyma was markedly disrupted by multifocal to coalescing white-yellow nodules (up to 2.5 cm diameter), characterized by a greasy appearance and a caseonecrotic centre. The urinary bladder was dilated, with clear, bright yellow contents and scattered fibrin-like material. The prostate was enlarged, firm and calcified upon sectioning. The prostatic parenchyma was effaced by multifocal white-yellow caseonecrotic nodules (up to 0.5 cm in diameter), similar to those observed in the kidneys. Mild congestion of the penile portion of the urethra. The right testicle was retained within the abdominal cavity (cryptorchid) and markedly reduced in size. No macroscopic lesions were observed in the central nervous system. Representative samples of the lung, liver, spleen, kidney and prostate were collected and fixed in 10% neutral buffered formalin and processed routinely.
5 Histopathology
Representative samples of the lung, liver, spleen, kidney, prostate and brain were collected and fixed in 10% neutral buffered formalin and processed routinely. Histopathological examination revealed multiple granulomatous lesions affecting all examined organs, (Figure 4) with no lesions observed in the brain. These lesions were composed predominantly of epithelioid cells and fewer multinucleated Langhans-type giant cells, often surrounding central areas of necrosis. At the periphery, granulomas were variably circumscribed by lymphocytes, plasma cells, fibroplasia and fibrosis. In the liver, kidney and prostate, large caseous and colliquative necrotic areas were seen with variable areas of central mineralisation (Figures 4b,d), multifocally associated with deposits of mineralised coarse granular basophilic material. In the kidneys and prostate, necrotic areas were multifocally associated with low to abundant infiltrates of degenerated neutrophils (suppuration). Cytology of urine collected at necropsy revealed a mixed inflammatory population, predominantly composed of macrophages, degenerate neutrophils and fewer small lymphocytes. Rare intracytoplasmic negatively stained rod-shaped structures were observed in the cytoplasm of the macrophages (suggestive of Mycobacteria spp.). Numerous bilirubin crystals and fewer calcium oxalate crystals were also detected. The lungs and spleen were characterised by disseminated small granulomatous nodules (Figure 4f). Ziehl–Neelsen staining (Bio-Optica, Milan, Italy) demonstrated numerous acid-fast bacilli within the cytoplasm of epithelioid and multinucleated giant cells as well as dispersed throughout the necrotic debris (Figures 4c,e, inset). No relevant histopathological findings were detected in brain sections.
Figure 4
6 Microbiological findings
Tissue samples from the dog were processed for both mycobacterial culture and molecular analysis by the National Reference Centre (CNR) for bovine tuberculosis in Italy, Istituto Zooprofilattico Sperimentale della Lombardia e dell’Emilia-Romagna (IZSLER). Briefly, a portion of each sample was degreased, shredded, and mechanically homogenised in physiological solution (1:2) using a stomacher for 2–5 min. The homogenate was divided into two aliquots, one subjected to decontamination for mycobacterial culture and the other used for direct molecular detection. For culture, the homogenate was decontaminated with 4% NaOH, neutralised, centrifuged, and the resulting pellet resuspended in phosphate buffer. Aliquots were inoculated onto Löwenstein–Jensen medium with pyruvate, Stonebrink medium, and liquid Middlebrook 7H9 MGIT, and incubated at 37 °C for up to 8 weeks.
In parallel, direct molecular detection performed on tissue homogenates by IS6110-based real-time PCR (34) revealed the presence of Mycobacterium tuberculosis complex (MTBC). Colonies compatible with MTBC growth were subsequently isolated in culture, and molecular identification confirmed the isolate as Mycobacterium tuberculosis. Following identification, bacterial colonies were suspended in Middlebrook 7H9 broth, heat-inactivated, sonicated, and subjected to DNA extraction using the NucleoSpin Tissue kit. DNA concentration was quantified fluorometrically. Whole genome sequencing libraries were prepared using the Illumina DNA Prep (M) Tagmentation kit and sequenced on MiniSeq platform, generating 2 × 150 base paired-end reads. Raw sequencing data, after quality and contamination check, respectively, with FastQC and Kraken, were subsequently sent to the IRCCS San Raffaele Scientific Institute and analysed using the MTBseq pipeline (35), with drug resistance interpretation based on the WHO mutation catalogue (36), and genetic relatedness assessed using Ridom Seqsphere+ software against a large local archive of WGS-characterised isolates, including those from Italy (37).
Genomic characterisation identified the isolate as Mycobacterium tuberculosis lineage 4.1.2.1 (Haarlem), with no resistance markers detected. Comparative analysis against national and international sequenced isolates revealed no genetically related strains based on core genome multilocus sequence typing (cgMLST) scheme at 5 and 12 allelic differences.
Further microbiological examination for aerobic microorganisms was performed on specimens and swabs collected during the post-mortem examination. Tissue aspirates were collected from lungs, liver and kidney and bladder contents with sterile swabs (Copan Italia S.p. A., Brescia, Italy).
Samples were then diluted in 1 mL of a nutrient broth (HIB, Heart Infusion Broth, Conda, Madrid, Spain), and 10 and 100 μL of bacterial suspensions were then inoculated into solid media and broths, respectively, as described below. The evaluation of aerobic microorganisms was conducted using a nutrient medium (BA, Blood Agar Base n°2, Biolife, Milan, Italy) with 5% defibrinated sheep blood (Allevamento Blood, Teramo, Italy), a nutrient broth (HIB), and selective Enterobacteriaceae media (McConkey agar, Oxoid, Basingstoke, UK). Cultures were inoculated and incubated at 37 ± 1 °C in aerobic conditions.
Bacterial culture yielded heavy growths of Escherichia coli (E. coli) and Providencia stuartii in the lungs with lesser growths of Klebsiella spp. Pseudomonas spp. was detected in the liver specimen. No other bacterial growth was observed in kidney and urine samples.
7 Epidemiological investigation: reverse zoonosis and zoonotic re-exposure
The epidemiological investigation conducted following the confirmed case of tuberculosis (TB) in the dog revealed that the animal was born and raised in the Veneto region and had never travelled abroad. The dog had been part of a stable household with two cohabiting owners for at least three years, both of whom were of Eastern European origin and frequently travelled to that region. One of the owners (A) had undergone treatment for severe active pulmonary TB in 2022. At that time, a contact investigation was initiated (January 2022), during which the second cohabitant (B) tested negative for TB infection (Quantiferon test and chest X-ray in February 2022; repeat Quantiferon in April 2022 also negative). At the time of the dog’s illness (September 2024), both owners (A and B) reported being asymptomatic (no cough, no fever). The dog was described as living both indoors and outdoors, frequently sharing space with a cat that appeared clinically healthy. The dog used to live in close contact with the owners. As part of the current investigation on October 2024, both owners underwent renewed TB screening (Quantiferon): the previously treated individual (A) showed no signs of active disease, while the second cohabitant (B) tested positive for latent TB infection and completed a preventive treatment regimen. In accordance with the protocol, owner B was re-evaluated in July 2025, with no clinical symptoms or abnormalities detected on routine examinations (Quantiferon negative). The results of the epidemiological investigation, including the documented infections within the household, are summarised in Figure 5.
Figure 5
8 Discussion
This case describes a clinically under-recognised manifestation of canine tuberculosis and introduces hypercalcaemia as a potential useful biomarker in dogs with systemic granulomatous disease. It further reinforces the relevance of a One Health perspective, advocating for closer cooperation between veterinary and human medicine to improve detection and control of zoonotic diseases.
A particularly novel and clinically significant finding was the marked hypercalcaemia, accompanied by hyperphosphataemia and an elevated Ca × P product. In human medicine, hypercalcaemia is a recognised marker of active tuberculosis, attributed to extra renal synthesis of calcitriol by activated macrophages within granulomas (23–25, 27–29, 38–40). Recently, hypercalcaemia has been documented in cases of granulomatous steatitis, in which serum PTH, when assessed, was either undetectable or within the normal range, as observed in our case (14, 41). This finding supports the hypothesis of hypervitaminosis D as a secondary consequence of the underlying granulomatous condition (14). Indeed, this observation aligns with previous reports describing hypercalcaemia (total and/or ionised) in association with several infectious or parasitic granulomatous conditions in dogs (14, 16–21). To date, although this phenomenon has been documented in disseminated infections caused by various Mycobacterium species (9), it has only been rarely reported in dogs with confirmed Mycobacterium tuberculosis infection. This observation may therefore represent a rare veterinary documentation of such a metabolic disturbance associated with disseminate canine tuberculosis, highlighting a potentially clinically significant aspect of host-pathogen interaction in this species. The presence of granulomatous inflammation in multiple organs supports a similar pathogenic mechanism to that described in humans. This finding may offer a new diagnostic clue in dogs presenting with unexplained hypercalcaemia and systemic granulomatous disease.
The anatomopathological findings indicated a systemic mycobacterial infection, with the liver, kidneys, and prostate being most severely affected organs, and disseminated miliary foci detected in the lung and spleen. This pattern of distribution affecting the liver, lung, and spleen is consistent with a hematogenous (embolic) dissemination and raises questions about the route of infection. The animal may have acquired infection via inhalation, followed by early haematogenous dissemination to extrapulmonary organs. Alternatively, the predominance of lesions in the liver, coupled with comparatively limited pulmonary involvement, is compatible with a primary oral route of infection. Moreover, the extensive renal and prostatic lesions, along with the detection of rod-shaped structures within macrophages in urinary cytology, suggest the potential for urinary dissemination of the pathogen.
The prolonged administration of corticosteroids for the management of chronic disease may have predisposed the dog to increased susceptibility to opportunistic infections. The diagnosis of mycobacterial infection, and in particular that of infection with MTBC-group organisms, is notoriously challenging to confirm, as all the available diagnostic tests are limited by sensitivity, specificity, or both (9).
The diagnosis of M. tuberculosis infection in companion animals remains complex due to its nonspecific clinical presentation, and the rarity of confirmed cases and official reports.
The present case contributes to the growing body of evidence suggesting that dogs infected with Mycobacterium tuberculosis may serve as sentinel hosts for undiagnosed human infections within shared environments (42). Reverse zoonotic transmission, whereby humans transmit M. tuberculosis to companion animals, as inferred from this investigation, has been documented in several other reports, underscoring the need to include pets in contact tracing protocols, particularly in households with prolonged or close human–animal interaction (2, 43). Although environmental persistence of M. tuberculosis is considered limited compared to other mycobacterial species, its survival in aerosols and fomites may still pose a risk under specific conditions (44–46). In our case, the dog lived in close contact with its MTB–positive owner, a factor that significantly increases the likelihood of reverse zoonotic transmission. Dogs, due to their close physical proximity to humans and shared living spaces, may inhale infectious droplets or ingest contaminated biological material released during coughing or sneezing episodes by infected individuals. Unfortunately, we could not confirm the epidemiological link by genotyping of the two strains, as data from owner A was not available. Nevertheless, this transmission dynamic is supported by documented cases in the literature, where canine tuberculosis was traced back to human sources within the same household (2, 3, 47).
The strain isolate from the dog was submitted to the IZSLER (Italian National Reference Centre for Bovine Tuberculosis) and IRCCS San Raffaele Scientific Institute (TB Supranational Reference Laboratory) enabled definitive diagnostic confirmation and strain characterisation. Whole genome analysis identified the agent as Mycobacterium tuberculosis lineage 4.1.2.1 (Haarlem), a lineage widely distributed in Eastern Europe. Comparative genomic analysis against the reference archive of over 15.000 MTBC genomes, including national and international isolates, revealed absence of genetically related strains. The genetically closest isolates identified were two Haarlem strains from Kosovo; however, even these exhibited a distance of 38 alleles, a divergence incompatible with any recent transmission event. This substantial allelic gap, together with the fact that MTBC genomes-data collection of Eastern European isolates is not systematic, further supports the interpretation that the detected strain is unlikely to be autochthonous. These findings strongly suggest that the dog’s strain corresponds to an imported or extra-Italian genotype, rather than one circulating locally. This interpretation is fully compatible with the Eastern European origin of the dog’s owner and his frequent travels to that region.
Similar to other documented cases, diagnosis was achieved late in the disease course, which likely exacerbated clinical deterioration and delayed public health intervention (48–50). Human TB exposure was not initially included in the dog’s clinical history because the owner’s previous tuberculosis diagnosis was unknown at the time of presentation; this information was not disclosed to the veterinarian and is not routinely collected during standard canine anamnesis. This circumstance highlights the need to improve the completeness of clinical, anamnesis and epidemiological data collection in companion animals, particularly to strengthen surveillance and early recognition of severe zoonotic diseases. In addition, early diagnosis of TB in companion animals could reduce suffering, improve outcomes, and enhance epidemiological surveillance (47, 51, 52). The intimate nature of the human–animal bond in domestic settings underscores the importance of considering pets as potential secondary hosts, especially in regions or communities with high TB prevalence. Including animals in contact tracing and epidemiological assessments may enhance early detection and containment strategies within a One Health framework.
In addition, the novelty of this case lies in the potential secondary transmission from the infected dog to a cohabiting human, suggesting that reverse zoonosis may evolve into zoonotic re-exposure within the same household, a dynamic rarely documented in the literature (2, 47, 53).
This case report presents several strengths and limitations that warrant careful consideration. The confirmed diagnosis of M. tuberculosis and the comprehensive clinicopathological characterisation provide valuable insights into the presentation of systemic tuberculosis in a companion animal. Importantly, this case highlights the need to implement more structured and standardised diagnostic and epidemiological protocols for companion animals. While such protocols are well established in human medicine and are routinely applied in veterinary public health for livestock and within official control systems (e.g., food safety surveillance), they are not yet harmonised for pets. This case therefore underscores the relevance of extending coordinated diagnostic and tracing approaches to companion animals as part of a One Health framework.
The case also presents inherent limitations. As a single clinical observation, its generalizability is restricted. Moreover, the M. tuberculosis isolate from the human index case was not available, preventing direct strain comparison and limiting the completeness of the epidemiological investigation. This constraint hampers the ability to definitively reconstruct the transmission pathway and fully contextualise the infection dynamics.
Overall, the integration of veterinary and human clinical expertise, diagnostic workflows, and epidemiological investigation underscores the pivotal role of interdisciplinary collaboration in managing zoonotic diseases. This synergistic approach enhances surveillance capacity and supports the refinement of diagnostic protocols, enabling earlier detection and more accurate characterisation of emerging infectious threats at the human–animal interface.
9 Conclusion
This case highlights a rare presentation of disseminated Mycobacterium tuberculosis infection in a dog, with hypercalcaemia serving as a potential useful clinicopathological diagnostic clue in cases of systemic granulomatous disease in canines, including those caused by Mycobacteria tuberculosis. The integration of veterinary syndromic surveillance combined with human medicine epidemiological oversight underscores the importance of One Health collaboration, serving as a wake-up call for improved cross-sector vigilance. Notably, the epidemiological investigations enabled the inference of a reverse zoonosis event, with evidence suggesting human-to-animal transmission followed by latent infection in a cohabiting individual, indicating possible perpetuation of the pathogen within the household. This reinforces the need to enhance zoonotic monitoring and refine diagnostic protocols for early detection and control of emerging infectious diseases across species at the human–animal interface.
Statements
Data availability statement
The datasets presented in this study can be found in online repositories. The names of the repository/repositories and accession number(s) can be found at: https://www.ncbi.nlm.nih.gov/, PRJNA1433394.
Ethics statement
The study was conducted in accordance with local legislation and institutional requirements. The owner provided written informed consent for clinical investigation, data use, and publication. All data are presented in anonymous and/or aggregated form. The manuscript includes an epidemiological investigation related to the canine case and contains no identifiable human images. Clinical information and biological samples were collected during routine clinical activities and epidemiological investigations. Clinicians obtained these materials for diagnostic purposes at the request of the animal’s owner. Gross pathology and histopathology images were collected and published with the explicit consent of the animal’s owner. All procedures involving animals complied with Directive 2010/63/EU of the European Parliament and of the Council on the protection of animals used for scientific purposes, as implemented in national legislation (D.L. 26/2014). Written informed consent was obtained from the participants for the publication of this case report.
Author contributions
EM: Writing – original draft, Software, Visualization, Formal analysis, Project administration, Validation, Conceptualization, Methodology, Writing – review & editing, Data curation, Investigation. TF: Writing – original draft, Methodology, Data curation, Investigation, Writing – review & editing, Conceptualization, Supervision. AM: Investigation, Methodology, Writing – review & editing. AB: Writing – review & editing, Methodology, Software, Investigation, Resources. FeM: Investigation, Writing – review & editing, Methodology. MC: Writing – review & editing, Methodology, Investigation. GF: Visualization, Data curation, Validation, Writing – review & editing, Methodology, Investigation. MM: Methodology, Investigation, Writing – review & editing. CB: Methodology, Writing – review & editing, Investigation. ES: Writing – review & editing. MS: Methodology, Investigation, Writing – review & editing. VC: Writing – review & editing, Methodology, Investigation. MB: Formal analysis, Resources, Visualization, Methodology, Supervision, Investigation, Data curation, Validation, Writing – review & editing. FMa: Validation, Methodology, Writing – review & editing, Data curation, Visualization, Software. AC: Resources, Software, Writing – review & editing, Data curation, Validation, Methodology, Visualization. DC: Methodology, Data curation, Supervision, Software, Visualization, Validation, Resources, Writing – review & editing. AN: Formal analysis, Writing – original draft, Project administration, Funding acquisition, Data curation, Resources, Methodology, Conceptualization, Investigation, Writing – review & editing, Supervision.
Funding
The author(s) declared that financial support was not received for this work and/or its publication.
Acknowledgments
We gratefully acknowledge the Veterinary Clinic and Laboratory San Marco for providing the clinical material and diagnostic imaging essential to the documentation and interpretation of this case. We also extend our sincere thanks to all the colleagues, medical doctors, veterinarians, technicians, and laboratory staff, who contributed to the clinical management, diagnostic workup, and multidisciplinary collaboration throughout the course of this investigation. Their expertise and commitment were instrumental in advancing our understanding of this rare presentation.
Conflict of interest
The author(s) declared that this work was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.
Generative AI statement
The author(s) declared that Generative AI was not used in the creation of this manuscript.
Any alternative text (alt text) provided alongside figures in this article has been generated by Frontiers with the support of artificial intelligence and reasonable efforts have been made to ensure accuracy, including review by the authors wherever possible. If you identify any issues, please contact us.
Publisher’s note
All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.
References
1.
EngelmannNOndrekaNMichalikJNeigerR. Intra-abdominal Mycobacterium tuberculosis infection in a dog. J Vet Intern Med. (2014) 28:934–8. doi: 10.1111/jvim.12347,
2.
HackendahlNCMawbyDIBemisDABeazleySL. Putative transmission of Mycobacterium tuberculosis infection from a human to a dog. J Am Vet Med Assoc. (2004) 225:1573–7, 1548–7. doi: 10.2460/javma.2004.225.1573,
3.
ErwinPCBemisDAMcCombsSBSheelerLLHimelrightIMHalfordSKet al. Mycobacterium tuberculosis transmission from human to canine. Emerg Infect Dis. (2004) 10:2258–10. doi: 10.3201/eid1012.040094
4.
ParsonsSDCWarrenRMOttenhoffTHMGey van PittiusNCvan HeldenPD. Detection of Mycobacterium tuberculosis infection in dogs in a high-risk setting. Res Vet Sci. (2012) 92:414–9. doi: 10.1016/j.rvsc.2011.03.026,
5.
JeffreyDCYingK. Tuberculosis Host-Pathogen Interactions. 1st ed. Cham: Springer Nature Switzerland AG (2019).
6.
RibeiroMGLimaMCFFrancoMMJMegidJSoaresLMMachadoLHAet al. Pre-multidrug-resistant Mycobacterium tuberculosis infection causing fatal enteric disease in a dog from a family with history of human tuberculosis. Transbound Emerg Dis. (2017) 64:e4–7. doi: 10.1111/tbed.12513
7.
ParsonsSDCGousTAWarrenRMvan HeldenPD. Pulmonary Mycobacterium tuberculosis (Beijing strain) infection in a stray dog. J S Afr Vet Assoc. (2008) 79:95–8. doi: 10.4102/jsava.v79i2.252,
8.
SykesJE. Cutaneous Mycobacterioses of cats and dogs. Vet Clin North Am Small Anim Pract. (2025) 55:237–49. doi: 10.1016/j.cvsm.2024.11.009,
9.
O’HalloranCBarkerENHopeJCGunn-MooreDA. Canine tuberculosis: a review of 18 new and 565 previously reported confirmed cases. Vet J. (2024) 304:106089. doi: 10.1016/j.tvjl.2024.106089
10.
O’HalloranCHopeJCDobromylskyjMBurrPMcDonaldKRhodesSet al. An outbreak of tuberculosis due to Mycobacterium bovis infection in a pack of English foxhounds (2016-2017). Transbound Emerg Dis. (2018) 65:1872–84. doi: 10.1111/tbed.12969
11.
BarkerENO’HalloranCGunn-MooreDA. Review canine tuberculosis - an emerging concern. Vet J. (2024) 305:106111. doi: 10.1016/j.tvjl.2024.106111,
12.
MoranNEFerketichAKWittumTEStullJW. Dogs on livestock farms: a cross-sectional study investigating potential roles in zoonotic pathogen transmission. Zoonoses Public Health. (2018) 65:80–7. doi: 10.1111/zph.12373,
13.
PosthausHBodmerTAlvesLOevermannASchillerIRhodesSGet al. Accidental infection of veterinary personnel with Mycobacterium tuberculosis at necropsy: a case study. Vet Microbiol. (2011) 149:374. doi: 10.1016/j.vetmic.2010.11.027,
14.
Reyes-HughesHBivandAWatersCValientePAdamFRapastellaSet al. Evaluation of presentation, treatment and outcome in dogs with granulomatous steatitis associated with hypercalcaemia: six cases (2019-2023). J Small Anim Pract. (2024) 65:704–12. doi: 10.1111/jsap.13771,
15.
FabrickCBugbeeAFosgateG. Clinical features and outcome of Heterobilharzia americana infection in dogs. J Vet Intern Med. (2010) 24:140–4. doi: 10.1111/j.1939-1676.2009.0429.x
16.
O’BrienMMcMichaelMLe BoedecK. (2018). 32:1684–1691. doi: 10.1111/jvim.15255
17.
MellanbyRJMellorPVilliersEJHerrtageMEHalsallDO’RahillySet al. (2006). 47:207–212. doi: 10.1111/j.1748-5827.2006.00019
18.
BoagAKMurphyKFConnollyDJ. Hypercalcaemia associated withAngiostrongylus vasorumin three dogs. J Small Anim Pract. (2005) 46:79–84. doi: 10.1111/j.1748-5827.2005.tb00297.x
19.
GrahamAMDavenportAMoshnikovaVSGilmourLJFabianiMBishopMAet al. Heterobilharzia americana infection in dogs: a retrospective study of 60 cases (2010-2019). J Vet Intern Med. (2021) 35:1361–7. doi: 10.1111/jvim.16127,
20.
FradkinJMBranieckiAMCraigTMRamiro-IbanezFRogersKSZoranDL. Elevated parathyroid hormone-related protein and hypercalcemia in two dogs with schistosomiasis. J Am Anim Hosp Assoc. (2001) 37:349–55. doi: 10.5326/15473317-37-4-349
21.
LindeKJKelleherTRPerryJA. Biological implant-associated granulomatous inflammation resulting in secondary hypercalcemia and azotemia in a dog. Clin Case Reports. (2018) 6:1801–6. doi: 10.1002/ccr3.1661,
22.
ClercxCCoignoulFJakovlevicSBalligandMMainilJHenroteauxMet al. Tuberculosis in dogs: a case report and review of the literature. Journal of the American Animal Hospital Association.(1992) 28:207–11.
23.
WadaTHanibuchiMSaijoA. Acute hypercalcemia and hypervitaminosis D associated with pulmonary tuberculosis in an elderly patient: a case report and review of the literature. J Med Investig. (2019) 66:351–4. doi: 10.2152/jmi.66.351,
24.
DayalDDidelSRAgarwalSSachdevaNSinghM. Acute Hypercalcaemia and Hypervitaminosis D in an infant with extra pulmonary tuberculosis. J Clin Diagn Res JCDR. (2015) 9:SD03–4. doi: 10.7860/JCDR/2015/15931.6680,
25.
ChanJYKanthayaM. Hypercalcaemic crisis in an elderly patient with pulmonary tuberculosis. Oxf Med Case Rep. (2015) 2015:354–7. doi: 10.1093/omcr/omv061,
26.
SalahFOAbdelaAFObeidZMAdaneLAregaG. Hypercalcemia in a 5-year-old child with disseminated tuberculosis: case report and literature review. Pediatr Health Med Ther. (2023) 14:477–81. doi: 10.2147/PHMT.S435222,
27.
JohnSMSagarSAparnaJKJoySMishraAK. Risk factors for hypercalcemia in patients with tuberculosis. Int J Mycobacteriology. (2020) 9:7–11. doi: 10.4103/ijmy.ijmy_211_19,
28.
TingSMSGopalakrishnanKZehnderD. Hypercalcemia in testicular tuberculosis. Kidney Int. (2015) 88:1203. doi: 10.1038/ki.2015.75,
29.
SivageethanSGnanathayalanSWFernandoMBulugahapitiyaU. Unravelling a hidden pathology of a vertebral fracture in a teenage girl. BMC Endocr Disord. (2024) 24:193. doi: 10.1186/s12902-024-01732-z,
30.
AbdullahASAdelAMHusseinRMAbdullahMAYousafAMudawiDet al. Hypercalcemia and acute pancreatitis in a male patient with acute promyelocytic leukemia and pulmonary tuberculosis. Acta Bio-Med Atenei Parm. (2018) 89:23–7. doi: 10.23750/abm.v89i3-S.7216,
31.
Anel-QuimpoJSandovalMASLantion-AngFL. Hypercalcaemia from genitourinary tuberculosis in a female with multiple exostoses. BMJ Case Rep. (2011) 2011:bcr1220103651. doi: 10.1136/bcr.12.2010.3651,
32.
SquiresRACrawfordCMarcondesMWhitleyN. 2024 guidelines for the vaccination of dogs and cats - compiled by the vaccination guidelines group (VGG) of the world small animal veterinary association (WSAVA). J Small Anim Pract. (2024) 65:277–316. doi: 10.1111/jsap.13718,
33.
World Organization of Animal Health (WOAH). Leptospirosis. Man Diagn Tests Vaccines Terr Anim [Internet]. (2021). Available online at: https://www.woah.org/fileadmin/Home/fr/Health_standards/tahm/3.01.12_LEPTO.pdf (Accessed April 15, 2026).
34.
FerrariSZanoniMMangeliAPigoliCD’IncauMAlboraliGLet al. Bacteriological culture and direct PCR for detecting the Mycobacterium tuberculosis complex in the Italian eradication campaign: a decade of experience at the National Reference Laboratory. J Appl Microbiol. (2024) 135:lxae064. doi: 10.1093/jambio/lxae064
35.
KohlTAUtpatelCSchleusenerVDe FilippoMRBeckertPCirilloDMet al. MTBseq: a comprehensive pipeline for whole genome sequence analysis of Mycobacterium tuberculosis complex isolates. PeerJ. (2018) 6:e5895. doi: 10.7717/peerj.5895,
36.
Global Programme on Tuberculosis and Lung Health (GTB). (2026). Catalogue of Mutations in Mycobacterium tuberculosis complex and their Association with Drug Resistance, 2nd ed [Internet]. 2nd edn. Available online at: https://www.who.int/publications/i/item/9789240082410 (Accessed January 5, 2026)
37.
GhodousiACannasATaglianiEBatignaniVBisogninFBorroniEet al. Comprehensive whole genome sequencing dataset of Mycobacterium tuberculosis strains collected across Italy. Sci Data. (2025) 12:624. doi: 10.1038/s41597-025-04966-1,
38.
PimentaGRoxoMIBirneRCarvalhoTJ. Urogenital tuberculosis in a patient with persistent sterile pyuria. BMJ Case Rep. (2025) 18:e264594. doi: 10.1136/bcr-2024-264594,
39.
AbdulfattahORahmanEUShwetaFDatarPAlnafoosiZTrauberDet al. Severe hypercalcemia in a patient with extrapulmonary Mycobacterium abscessus: granuloma or immune reconstitution inflammatory syndrome? First case of Mycobacterium abscessus presenting as retroperitoneal lymphadenopathy with severe hypercalcemia: a case report and literature review. J Community Hosp Intern Med Perspect. (2018) 8:331–8. doi: 10.1080/20009666.2018.1539057,
40.
MartineauAR. "Chapter 98 - vitamin D and tuberculosis". In: HewisonMBouillonRGiovannucciEGoltzmanDMeyerMWelshJ, editors. Feldman and Pike’s Vitamin D (Fifth Edition) [Internet]. London: Academic Press (2024)
41.
BrudvigJMLangloisDKJaffeyJAMiksicekVARefsalKRMackeyPEet al. Endogenous calcitriol production and ionized hypercalcemia in 7 dogs with chronic dermatopathy of infectious and noninfectious etiology (2016-2024). J Vet Intern Med. (2026) 40:aalag038. doi: 10.1093/jvimsj/aalag038,
42.
BritesDLoiseauCMenardoFBorrellSBoniottiMBWarrenRet al. A new phylogenetic framework for the animal-adapted Mycobacterium tuberculosis complex. Front Microbiol. (2018) 9:2820. doi: 10.3389/fmicb.2018.02820,
43.
MartinezLVermaRCrodaJHorsburghCRWalterKSDegnerNet al. Detection, survival and infectious potential of Mycobacterium tuberculosis in the environment: a review of the evidence and epidemiological implications. Eur Respir J. (2019) 53:1802302. doi: 10.1183/13993003.02302-2018,
44.
LanYRancuIChitwoodMHSobkowiakBNyhanKLinHHet al. Integrating genomic and spatial analyses to describe tuberculosis transmission: a scoping review. Lancet Microbe. (2025) 6:101094. doi: 10.1016/j.lanmic.2025.10109
45.
BuiVLHughesAERagonnetRMeehanMTHendersonAMcBrydeESet al. Agent-based modelling of Mycobacterium tuberculosis transmission: a systematic review. BMC Infect Dis. (2024) 24:1394. doi: 10.1186/s12879-024-10245-y,
46.
ColemanMMartinezLTheronGWoodRMaraisB. Mycobacterium tuberculosis transmission in high-incidence settings-new paradigms and insights. Pathogens. (2022) 11:1228. doi: 10.3390/pathogens11111228,
47.
ZmakLGomercic PalcicMObrovacMFolnozicIStrelecDReilIet al. First confirmed case of zoonotic transmission of RR-TB from a dog to a human, a neglected mode of Mycobacterium tuberculosis infection-case report and review of the literature. Pathogens. (2025) 14:684. doi: 10.3390/pathogens14070684,
48.
MartinhoAPVFrancoMMJRibeiroMGPerrottiIBMMangiaSHMegidJet al. Disseminated Mycobacterium tuberculosis infection in a dog. Am J Trop Med Hyg. (2013) 88:596–600. doi: 10.4269/ajtmh.12-0332,
49.
MentulaSKarkamoVSkrzypczakTSeppänenJHyyryläinenHLHaanperäMet al. Emerging source of infection – Mycobacterium tuberculosis in rescue dogs: a case report. Access Microbiol. (2020) 2:acmi000168. doi: 10.1099/acmi.0.000168,
50.
HaydockLAJAbrams-OggACGWeeseJSGoldsteinMRCliffordABSebastianAet al. Diagnostic and public health investigation of Mycobacterium tuberculosis infection in a dog in Ontario, Canada. J Vet Diagn Invest. (2022) 34:292–7. doi: 10.1177/10406387221074706,
51.
VangoneLCardilloLRiccardiMGBorrielloGCerroneACoppaPet al. Mycobacterium tuberculosis SIT42 infection in an abused dog in southern Italy. Front Vet Sci. (2021) 8:653360. doi: 10.3389/fvets.2021.653360,
52.
MarfilMJBarandiaranSZumárragaMJGermaniLFacciniTLinaresMet al. Mycobacterium tuberculosis infection in a free-ranging urban dog from Argentina. Vet Res Commun. (2022) 46:781–8. doi: 10.1007/s11259-022-09898-4,
53.
MessengerAMBarnesANGrayGC. Reverse zoonotic disease transmission (zooanthroponosis): a systematic review of seldom-documented human biological threats to animals. PLoS One. (2014) 9:e89055. doi: 10.1371/journal.pone.0089055,
Summary
Keywords
dog, hypercalcaemia, Mycobacterium tuberculosis, one health, reverse zoonosis, zoonotic transmission
Citation
Mazzotta E, Furlanello T, Mazzei A, Barberio A, Martignago F, Campalto M, Foiani G, Moronato ML, Battistella C, Santinon E, Sabia M, Carta V, Boniotti MB, Di Marco F, Cabibbe AM, Cirillo DM and Natale A (2026) Case Report: Epidemiologically inferred reverse zoonosis and intra-household zoonotic re-exposure of Mycobacterium tuberculosis in a domestic dog: a one health alert and the diagnostic potential of hypercalcaemia. Front. Vet. Sci. 13:1824722. doi: 10.3389/fvets.2026.1824722
Received
06 March 2026
Revised
27 April 2026
Accepted
28 April 2026
Published
18 June 2026
Volume
13 - 2026
Edited by
Francisco Javier Salguero, UK Health Security Agency (UKHSA), United Kingdom
Reviewed by
Shamim Sarkar, Lincoln Memorial University, United States
Alexander Teh, The University of Sydney, Australia
Updates
Copyright
© 2026 Mazzotta, Furlanello, Mazzei, Barberio, Martignago, Campalto, Foiani, Moronato, Battistella, Santinon, Sabia, Carta, Boniotti, Di Marco, Cabibbe, Cirillo and Natale.
This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: Elisa Mazzotta, emazzotta@izsvenezie.it
Disclaimer
All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.