Introduction

In January 2024, zoonotic tuberculosis (TB) was confirmed in a laboratory worker, representing the first detection under the Republic of Korea’s updated zoonotic TB surveillance system. The previous surveillance system focused on TB screening of humans who had been in contact with Mycobacterium bovis-infected cattle, such as livestock farm owners. In contrast, the enhanced surveillance system extended testing to high-risk occupational groups to detect M. bovis using spoligotyping and whole genome sequencing (WGS) of culture-positive Mycobacterium tuberculosis complex (MTBC) strains.

Zoonotic TB refers to TB transmitted from animals to humans, primarily through M. bovis [1]. The main hosts of M. bovis are cattle [2]. However, other animals, including livestock (e.g., deer and goats), pets (dogs and cats), and wildlife (wild boars and water deer), can also serve as reservoirs [3], complicating control and management efforts due to the complexity of transmission pathways.

The definitive diagnosis of zoonotic TB requires the isolation and identification of TB strains from human sputum cultures. However, differentiating between M. tuberculosis and M. bovis is challenging because of their similar clinical and radiological characteristics [4]. Both species belong to the MTBC and have genomes that are 99.9% identical at the nucleotide level [5]; thus, their differentiation using conventional laboratory tests is difficult. To confirm the presence of M. bovis, the Korea Disease Control and Prevention Agency (KDCA) relies on identifying its characteristic pyrazinamide resistance and employs spoligotyping and WGS for definitive analysis.

M. bovis is commonly transmitted through the ingestion of contaminated food, direct contact, or airborne exposure. Risk factors include consuming products from infected animals that are not fully cooked (e.g., dairy products such as cheese and milk) and percutaneous exposure via skin injuries during necropsy, slaughter, or laboratory work performed without appropriate personal protective equipment (PPE).

According to the European Union One Health 2023 Zoonoses Report published by the European Food Safety Authority and the European Center for Disease Prevention and Control, 138 confirmed human cases of zoonotic TB caused by M. bovis or Mycobacterium caprae were reported in 2023, corresponding to an incidence rate of 0.04 cases per 100,000 in the European Union and representing a 6.1% decrease in the notification rate from 2022 [6]. The Global Tuberculosis Report 2020, released by the World Health Organization, indicated that approximately 140,000 cases (1.4%) of zoonotic TB were confirmed among new TB cases in 2019, with about 11,400 (8.1%) deaths [7]. However, due to the lack of a zoonotic TB surveillance system in the Republic of Korea, the exact incidence of zoonotic TB in the country remains unknown [3].

To address this issue, the Division of Tuberculosis Policy of the KDCA has strengthened the surveillance framework for high-risk groups as part of its national TB control strategy. In collaboration with the Animal and Plant Quarantine Agency and the Ministry of Environment, the KDCA developed the Joint Epidemiological Investigation Manual for Zoonotic Tuberculosis in May 2023. This resource expands the genetic testing of TB strains to include workers in livestock and zoo settings, aiming to quantify zoonotic TB cases, improve contact management, and analyze transmission pathways.

Although zoonotic TB is relatively rare and may not appear to represent a major public health concern, the expansion of the livestock industry and increasing human-animal interactions heighten the risk of transmission [8]. Therefore, analyzing the surveillance system, transmission routes, and clinical characteristics of this first confirmed case under the enhanced system may provide key insights for future prevention and management.

Materials and Methods

Study Design and Population

In this retrospective study, we analyzed data from a 56-year-old female laboratory worker with confirmed zoonotic TB in January 2024, including the infection route and contacts. Fifteen individuals were identified as contacts, comprising 8 close contacts and 7 casual contacts.

This study systematically outlines the detection process and transmission route of zoonotic TB for laboratory workers through the Republic of Korea’s national notifiable infectious disease surveillance system.

Case Definition

According to the National Tuberculosis Management Guidelines, zoonotic TB is defined as the identification of M. bovis through genetic analysis of a culture-positive TB strain [3]. A contact refers to anyone who shared living spaces or had regular, prolonged, and direct contact with a patient with TB in an indoor environment within 3 months prior to TB diagnosis [1].

Data Collection

Following laboratory confirmation of zoonotic TB in the patient on January 10, 2024, an in-depth investigation was conducted in accordance with the Joint Response Manual to trace the infection source and transmission route. In cooperation with the KDCA Division of Tuberculosis Policy, local health authorities coordinated with the institution where the patient worked, conducting site visits, interviews with the patient, data verification, and comprehensive investigations to hypothesize potential transmission pathways and shared exposure sources. In line with the National Tuberculosis Management Guidelines, the 15 identified contacts underwent chest X rays, sputum tests, and interferon gamma release assay (IGRA) testing.

Spoligotyping and WGS

Spoligotyping was performed using a spoligotyping kit (Ocimum Biosolutions) in accordance with the manufacturer’s protocol, and the results were analyzed using the SITVIT2 and TB-Insight databases. WGS was performed using the Illumina Miseq system (Illumina Inc.) from a purified library prepared with the Illumina DNA Prep kit (Illumina Inc.). Subsequently, core genome multilocus sequence typing (cgMLST) based on 2,621 loci was analyzed using Ridom SeqSphere+ ver. 8.5.0 (Ridom GmbH).

Ethics Statement

This study was approved by the Institutional Review Board of the KDCA (No. KDCA-2024-10-02-P-01) and was performed in accordance with the principles of the Declaration of Helsinki. It involved an epidemiological investigation conducted in compliance with the Tuberculosis Prevention Act and the Korean National Tuberculosis Management Guidelines for TB control. Written informed consent was obtained from the patient.

Results

Effectiveness of the Enhanced Zoonotic TB Surveillance System

The previous surveillance system focused on conducting TB tests (X-ray and sputum culture when necessary) among individuals in contact with M. bovis-infected livestock, such as farmworkers. The enhanced system was established to proactively address zoonotic TB and to more effectively manage high-risk occupational groups. In May 2023, a Joint Response Manual was developed in collaboration with relevant agencies, and in June 2023, epidemiological survey forms were updated to capture the occupations of patients with TB, such as those working in livestock-related fields [9,10]. Additionally, protocols were updated to mandate that culture-positive strains be referred to the Bacterial Analysis Division via the Comprehensive Disease and Health Management System. In 2016, genetic testing of TB strains covered only patients with TB in institutional settings; this was gradually expanded to include children under 5 years of age in 2019. The 2023 revisions further expanded testing to include patients with multidrug resistant TB and groups at high risk of zoonotic TB (Table 1). Furthermore, upon detecting TB in livestock, human contacts such as farmworkers are now screened using chest X-rays, sputum tests, and, if necessary, IGRA for latent TB infection (LTBI).

Detection, Assessment, Confirmation, and Reporting

The patient in this case had been undergoing regular follow-up visits at the university hospital for rheumatic disease, and on January 31, 2023, a chest X-ray revealed findings suggestive of TB (no cavity observed). Subsequent sputum smear tests performed using self-collected samples on February 1, 2023, returned negative results. Bronchoscopy was performed on February 22, 2023. Although an acid fast bacillus (AFB) smear and TB polymerase chain reaction (a nucleic acid amplification test for TB) were negative, her AFB culture was positive. Consequently, she was diagnosed with pulmonary TB on March 24, 2023.

According to the National Tuberculosis Management Guidelines, rapid drug susceptibility testing for isoniazid and rifampin, along with conventional drug susceptibility testing, is performed on the first culture for all patients with TB [1]. Rapid drug susceptibility testing indicated no resistance to isoniazid or rifampin. While conventional drug susceptibility results were inconclusive, WGS confirmed pyrazinamide resistance.

Spoligotyping results confirmed the BOV-3 clade and the M. bovis lineage; additional analysis using WGS revealed that the Rd4 region was deleted and identified a sequence mutation (C→G) at base 169 of the pncA gene, a characteristic of M. bovis associated with intrinsic pyrazinamide resistance. In the cgMLST analysis, the strain isolated from the patient (E2306) was closely related to strains isolated from animals in the Republic of Korea (Figure 1).

The patient remained asymptomatic and exhibited no specific TB related symptoms apart from those associated with her preexisting rheumatic disease, for which she was not on immunosuppressive therapy. She began a 6 month regimen of isoniazid, rifampin, ethambutol, and pyrazinamide on March 24, 2023, and completed treatment without hospitalization.From March 24 to April 7, 2023, the patient was restricted from working to prevent transmission. On April 10, 2023, a physician confirmed that she was no longer infectious, allowing her to resume work and her regular activities.

Upon reporting the case on March 23, 2023, the local health authority identified the patient as belonging to a group at high risk of zoonotic TB. Subsequently, in June 2023, her TB-positive culture was submitted for genetic analysis—including spoligotyping and WGS—via the Comprehensive Disease and Health Management System to the KDCA Division of Bacterial Disease. On January 10, 2024, genetic testing revealed M. bovis infection, thereby confirming zoonotic TB (Figure 2).

Response and Investigation

The contact investigation period covered the 4 weeks (28 days) preceding the earliest diagnostic test (either sputum smear or chest X ray), spanning a total of 11 weeks from January 3, 2023, to March 24, 2023. One household contact was asymptomatic and tested negative for TB (via chest X ray) and LTBI (via IGRA).

In the workplace, 15 of the patient’s colleagues were identified as contacts. Among these, 8 who worked closely with the index patient in the same laboratory were classified as close contacts, while the remaining 7—who interacted casually during lunch breaks or incidental encounters within the same building—were categorized as casual contacts.

Close contacts underwent both TB and LTBI testing, along with follow up TB testing, whereas casual contacts were tested only for TB. Initial TB testing was conducted on April 15, 2023, and follow up testing on August 2, 2023. All 15 workplace contacts tested negative for TB. Among the 8 close contacts, 1 had a history of TB treatment and was not subjected to LTBI testing; of the remaining 7 individuals, 2 received a positive IGRA result, yielding a positivity rate of 28.6%. Both of these contacts completed LTBI treatment between May and August 2023 (Table 2).

Transmission Pathway

The patient had no personal or family history of TB. Genetic analysis of the TB strain using spoligotyping and WGS confirmed the presence of the M. bovis genotype, suggesting a negligible likelihood of association with Bacillus Calmette–Guérin vaccination. Moreover, the patient reported that she dislikes milk and had no history of consuming unpasteurized milk, raw meat, or animal by products. She also had no history of handling animals, visiting farms with open skin wounds, or direct contact with pets, wild animals, or M. bovis infected livestock. Consequently, her likelihood of exposure through previous zoonotic TB cases, direct contact with infected livestock, or exposure to livestock by-products was very low.

The investigation additionally indicated a high likelihood of exposure through laboratory work. The patient had worked in a laboratory setting for approximately 20 years, since 2002, and was involved in specimen processing. She primarily assisted with IGRA and serological testing (e.g., separating blood samples drawn with syringes) and performed histopathological examinations (processing lung nodules).

Although the patient consistently wore disposable gloves and gowns to prevent accidents involving needles or scalpels and to minimize exposure to animal fluids, she reported having experienced needle-stick incidents in the past. Individuals engaged in laboratory work face a risk of exposure to M. bovis-infected body fluids from contaminated needles, accidental splashes of biological material into the eyes, or unnoticed skin abrasions, all of which could serve as entry points for the pathogen.

Given the variable latency period of TB infection, which depends on an individual’s immune status, the exact timing of infection remains unclear. However, the patient likely acquired the infection through direct or percutaneous exposure to contaminated biological materials in a confined laboratory environment, with the infection remaining latent until immunosuppression triggered its progression to active TB.

Discussion

Between 1993 and 2004, studies in the United Kingdom reported the incidence of zoonotic TB among farmers and farm workers exposed to M. bovis-infected cattle; however, it remains unclear whether LTBI was diagnosed or whether LTBI testing was performed in those cases [11]. In contrast, an outbreak of M. bovis among zoo animals in the Republic of Korea from July 2021 to September 2022 presented a different scenario. Of the 21 exposed zoo workers tested, 6 (20.7%) were positive for LTBI on the initial IGRA screening, and an additional case (raising the positivity rate to 24.1%) was detected during follow-up [12]. Although the prolonged latency of TB complicates the determination of the exact timing of infection, these findings underscore the need for vigilant monitoring of occupational groups at high risk of exposure to zoonotic TB.

Based on the investigation of the infection source in this study, our patient likely acquired the infection through occupational exposure. Further studies are needed to investigate the risks associated with co exposure to livestock and their by products, in order to better define transmission routes and assess the risk of infection in individuals exposed to M. bovis through multiple pathways. In addition, individuals at high risk of exposure to zoonotic TB—such as laboratory workers and farm workers—should be educated about the importance of wearing personal protective equipment, including gowns and mask, gloves etc., to support the prevention, detection, and response to zoonotic infections.

Internationally, sporadic cases of zoonotic TB associated with M. bovis have been reported among individuals with occupational exposure. Examples include a case from New Zealand in 2015 involving a woman in her 50s who worked in a facility processing animal organs (mainly beef) for 7 years [13], a case from the United Kingdom in 2009 involving a 42-year-old veterinary nurse who conducted TB testing on cattle and handled an injured badger [14], and a case involving a 25-year-old veterinarian in the United Kingdom in 2011 who contracted M. bovis while performing invasive procedures (e.g., testing, intravenous injection, and autopsy) on infected alpacas without proper PPE [15]. These cases illustrate the varied contexts in which occupational exposure can lead to zoonotic TB transmission.

This study encountered several limitations. The slow growth and challenging culture conditions of TB bacteria, combined with the difficulty of differentiating M. bovis infection from human M. tuberculosis using standard laboratory tests, posed significant challenges. First, the substantial delay between the initial TB diagnosis and genotyping hindered prompt epidemiological investigation and response. Second, this delay resulted in the confirmation of zoonotic TB after the patient’s treatment had concluded. This case emphasizes the need for faster diagnostic processes, as early identification of M. bovis is crucial for managing drug-resistant TB. If the causative pathogen is not promptly identified as M. bovis and treatment is initiated with pyrazinamide, there is a risk of treatment failure and progression to drug-resistant TB. This was evidenced by a case of zoonotic TB in Peru in 2009, in which initial symptom improvement was followed by relapse during second-line treatment, ultimately resulting in respiratory failure and death in 2012 [16]. Additionally, although this study systematically reviewed the epidemiological investigation process, it only covers a single case and limits the generalizability of the findings. Further research, including large-scale cohort studies, is needed to identify various risk factors related to zoonotic TB transmission in high-risk occupational settings.

Nevertheless, this study provides meaningful implications. First, it is the initial response to zoonotic TB using the Joint Epidemiological Investigation Manual launched in May 2023, and the updated legal investigation form announced in June 2023. Second, it systematically organizes the process from detection, assessment, confirmation, response and investigation of the first zoonotic tuberculosis case identified through the enhanced national notifiable infectious diseases surveillance system. Third, it emphasizes the need for an enhanced surveillance system and the importance of further strengthening the surveillance system.

Conclusion

From a public health perspective, this study underscores the need for sophisticated surveillance and appropriate interventions to control zoonotic TB. It also requires education of people who are occupationally exposed to zoonotic diseases about the importance of wearing appropriate PPE. Integrating these strategies can reduce the risk of zoonotic diseases and improve the preemptive response to emerging threats.

HIGHLIGHTS

• We report the first case of zoonotic tuberculosis (TB) in a laboratory worker following an update to the Republic of Korea’s zoonotic TB surveillance system.

• Under the previous system, TB testing was conducted on humans in contact with Mycobacterium bovis-infected livestock. With the improved system, testing was extended to high-risk occupational groups using genetic analysis to identify M. bovis in culture-positive cases.

• Epidemiological investigation suggested that this infection likely resulted from occupational exposure.

• Effective prevention, early detection, and appropriate response to zoonotic TB in high-risk groups require collaboration among relevant agencies and the implementation of a One Health approach.

Article information

Ethics Approval

This study was approved by the Institutional Review Board of the KDCA (No. KDCA-2024-10-02-P-01) and was performed in accordance with the principles of the Declaration of Helsinki. The epidemiological investigation was conducted in compliance with the Tuberculosis Prevention Act and the Korean National Tuberculosis Management Guidelines for tuberculosis control. Written informed consent was obtained from the patient.

Conflicts of Interest

The authors have no conflicts of interest to declare.

Funding

None.

Availability of Data

All data generated or analyzed during this study are included in the published article. Additional data may be requested from the corresponding author.

Authors’ Contributions

JYL, YJP; Data curation: JYL, JK, SWP; Formal analysis: JYL, SWP; Investigation: JYL, JK; Methodology: JYL, YJP, SWP; Project administration: JL, JK; Resources: JYL, SWP, JK, YJP; Software: JYL; Supervision: JK, YJP; Validation: JK, YJP; Visualization: JYL, SWP; Writing–original draft: JYL; Writing–review & editing: all authors. All authors read and approved the final manuscript.

Additional Contributions

We extend our gratitude to the laboratory staff and officials at the local public health clinics for their valuable cooperation during the investigation.

Figure 1.

Phylogenetic analysis of Mycobacterium bovis strains. The core genome multilocus sequence typing of M. bovis was analyzed using Ridom SeqSphere+ ver. 8.5.0 (Ridom GmbH). A phylogenetic tree was constructed using the M. bovis whole genome sequences registered in the National Center for Biotechnology Information database with the unweighted pair-group method with arithmetic mean method based on 2,612 loci for the Mycobacterium tuberculosis complex.

Figure 2.

Timeline of the detection of zoonotic tuberculosis.

TB, tuberculosis; KDCA, Korea Disease Control and Prevention Agency; WGS, whole genome sequencing; M. bovis, Mycobacterium bovis; APQA, Animal and Plant Quarantine Agency; ME, Ministry of Environment.

References

• 1. Korea Disease Control and Prevention Agency (KDCA) (KR). 2024 National tuberculosis management guidelines [Internet]. KDCA; 2024 [cited 2024 Jul 22]. Available from: https://url.kr/xmxrla. Korean.
• 2. Centers for Disease Control and Prevention (CDC) (US). About bovine tuberculosis in humans [Internet]. CDC; 2024 [cited 2024 May 20]. Available from: https://www.cdc.gov/tb/about/m-bovis.html.
• 3. Korea Disease Control and Prevention Agency (KDCA), Animal and Plant Quarantine Agency (APQA), Ministry of Environment (ME) (KR). Zoonotic disease (3. Zoonotic tuberculosis) Joint Epidemiological Investigation manual [Internet]. KDCA; 2023 [cited 2024 May 31]. Available from: https://url.kr/lqdqvu. Korean.
• 4. Grange JM. Mycobacterium bovis infection in human beings. Tuberculosis (Edinb) 2001;81:71−7. ArticlePubMed
• 5. Garnier T, Eiglmeier K, Camus JC, et al. The complete genome sequence of Mycobacterium bovis. Proc Natl Acad Sci U S A 2003;100:7877−82. ArticlePubMedPMC
• 6. European Food Safety Authority (EFSA), European Centre for Disease Prevention and Control (ECDC). The European Union One Health 2023 Zoonoses report. EFSA J 2024;22:e9106. ArticlePubMedPMCPDF
• 7. World Health Organization (WHO) (CH). Global tuberculosis report 2020 [Internet]. WHO; 2019 [cited 2024 Jul 22]. Available from: https://www.who.int/publications/i/item/9789240013131.
• 8. Vayr F, Martin-Blondel G, Savall F, et al. Occupational exposure to human Mycobacterium bovis infection: a systematic review. PLoS Negl Trop Dis 2018;12:e0006208. ArticlePubMedPMC
• 9. Korean Law Information Center (KLIC) (KR). Enforcement Rules of the Tuberculosis Prevention Act, Forms No. 1 “Notification and Report of Tuberculosis report, etc.” [Internet]. KLIC; 2024 [cited 2024 Oct 7]. Available from: https://www.law.go.kr/%EB%B2%95%EB%A0%B9/%EA%B2%B0%ED%95%B5%EC%98%88%EB%B0%A9%EB%B2%95%20%EC%8B%9C%ED%96%89%EA%B7%9C%EC%B9%99/(00979,20231201). Korean.
• 10. Korean Law Information Center (KLIC) (KR). Enforcement Rules of the Tuberculosis Prevention Act, Forms No. 2 “Case Investigation Report of Tuberculosis Patients, etc.” [Internet]. KLIC; 2024 [cited 2024 Sep 10]. Available from: https://www.law.go.kr/%EB%B2%95%EB%A0%B9/%EA%B2%B0%ED%95%B5%EC%98%88%EB%B0%A9%EB%B2%95%20%EC%8B%9C%ED%96%89%EA%B7%9C%EC%B9%99/(00979,20231201). Korean.
• 11. UK Health Security Agency (UKHSA) (GB). Prevalence of latent tuberculosis (TB) infection in occupational groups who have prolonged indoor contact with cows: a rapid review [Internet]. UKHSA; 2023 [cited 2024 Sep 10]. Available from: https://assets.publishing.service.gov.uk/media/650acd48fbd7bc0013cb51dd/prevalence-of-TB-in-occupational-groups-indoor-contact-with-cows-rapid-review.pdf.
• 12. Lee HY, Kwon Y, Lee SE, et al. A Mycobacterium bovis outbreak among exhibition animals at a zoo in the Republic of Korea: the first contact investigation of zoonotic tuberculosis. Osong Public Health Res Perspect 2024;15:248−59. ArticlePubMedPMCPDF
• 13. Chan HH, Mpe J. A rare cause of pulmonary tuberculosis. N Z Med J 2015;128:81−3.
• 14. Shrikrishna D, de la Rua-Domenech R, Smith NH, et al. Human and canine pulmonary Mycobacterium bovis infection in the same household: re-emergence of an old zoonotic threat? Thorax 2009;64:89−91. ArticlePubMed
• 15. Twomey DF, Higgins RJ, Worth DR, et al. Cutaneous TB caused by Mycobacterium bovis in a veterinary surgeon following exposure to a tuberculous alpaca (Vicugna pacos). Vet Rec 2010;166:175−7. ArticlePubMedPDF
• 16. Shrestha A, Picoy J, Torres A, et al. A case report of transmission and disease caused by Mycobacterium caprae and Mycobacterium bovis in Lima, Peru. BMC Infect Dis 2021;21:1265. ArticlePubMedPMCPDF

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