Tuberculosis
Mycobacterium tuberculosis complex
Profile
Tuberculosis (TB) is the most common fatal infectious disease in humans worldwide. There are different tuberculosis pathogens that are categorised as part of the Mycobacterium tuberculosis complex (MTC). The most common pathogen causing tuberculosis in humans is Mycobacterium (M.) tuberculosis. The bacterium can be inactivated by pasteurisation (brief heating to 72 °C); however, it is insensitive to dehydration or cold.
Occurrence
Tuberculosis is widespread worldwide, especially in Africa, Asia and Latin America. According to estimates by the World Health Organisation (WHO), more than a third of the world's population is infected with tuberculosis(M. tuberculosis). Every year, 1.3 million people die from the infection and around 10 million are newly infected.
In Europe, the bovine tuberculosis pathogen(M. bovis) was greatly reduced after the Second World War, as a result of which many countries received the officially recognised status "free of bovine tuberculosis". In 1999, Austria's cattle herd received the status "officially recognised free of bovine tuberculosis" from the EU, and since then this tuberculosis pathogen has no longer been detected in any Austrian cattle herd. With the new Animal Health Law of the European Union, Austria has the status of "disease-free" with regard to infections with the Mycobacterium tuberculosis complex(M. bovis, M. caprae and M. tuberculosis).
Since 2008, however, M. caprae has been transmitted between red deer and cattle in individual areas of the provinces of Tyrol and Vorarlberg, and M. microti has also been detected sporadically in wild animals, cattle, cats and New World camelids. However, these detections are irrelevant for Austria's recognised free status.
Pathogen reservoir
Humans are the only relevant reservoir for M. tuberculosis. For mycobacteria that can be transmitted from animals to humans, such as M. bovis and M. caprae, cattle, wild boar, goats or wild ruminants (especially red deer) are the pathogen reservoir. The reservoir for M. microti is formed by voles and shrews, for example.
Route of infection
Whether an infection occurs depends on the frequency and intensity of contact, the amount of inhaled or orally ingested pathogens and the immune status of the person affected. Infection usually occurs through the inhalation of fine droplets in the air that are released when people suffering from open pulmonary tuberculosis cough and sneeze. Open pulmonary tuberculosis refers to diseases in which pathogens can be detected in the sputum. Transmission is also possible through the consumption of raw (unpasteurised) milk from cattle infected with tuberculosis.
Infection from animal to animal occurs preferably by the aerogenic route through inhalation of fine droplets containing the pathogen, which are coughed up by sick animals. However, it can also occur through contact or orally, e.g. via contaminated feed in feeding troughs and salt licks.
Symptomatology
Humans: In humans, the disease most commonly manifests as pulmonary tuberculosis. The affected person actively coughs up mycobacteria. The main symptoms are a persistent cough, fever, night sweats and unintentional weight loss. Other mostly unspecific symptoms include fatigue, loss of performance, swollen lymph nodes and a reduced general condition. If the infection is controlled by the immune system and the pathogens are trapped in granulomas (tubercles), for example, the mycobacteria remain in a dormant state ("latent tuberculosis"). Under certain conditions (e.g. immunosuppression or old age), reactivation can occur years later, with the disease re-emerging as secondary (post-primary) tuberculosis.
Before the implementation of control programmes and the pasteurisation of milk, infection with bovine tuberculosis pathogens (e.g. M. bovis) mainly resulted in manifestations outside the lungs (e.g. lymph node, intestinal or bone tuberculosis).
Animal: Chronic pulmonary tuberculosis in cattle is mainly characterised by progressive coughing and a slowly deteriorating general condition. However, disease processes can also occur in other organs. In cattle, tuberculosis can remain latent or subclinical for years.
An infection with mycobacteria should also be considered in camelids if they are in poor condition and emaciated. Respiratory symptoms may occur.
In cats, symptoms such as emaciation, deterioration in general condition, coughing and (palpable) circumferential enlargements in all parts of the body occur. Therapy-resistant skin changes have also been observed.
Infected red deer often show no specific symptoms in the early stages of the disease. In advanced cases, they may be in poor condition, emaciated and weakened.
Therapy
As mycobacteria are located intracellularly in tissues with poor blood supply (e.g. granulomas), they are difficult for drugs to reach. Treatment therefore takes several months and there is an increased risk of antibiotic resistance developing. If tuberculosis is confirmed, a combination therapy with several specifically effective antibiotics, so-called antituberculotics, must therefore be carried out. The duration of treatment is usually at least six months in order to prevent a relapse and the development of resistant pathogens.
Tuberculosis is a notifiable animal disease. Official control focuses on the identification and culling of infected animals, as drug therapy is not effective for animal welfare, pharmaceutical and epidemiological reasons.
Human
In 2025, 384 cases of tuberculosis in humans were reported to the Epidemiological Reporting System (EMS) (as at 15 April 2026), corresponding to 4.2 cases per 100,000 population. Of these, 326 cases could be definitively attributed to the Mycobacterium tuberculosis complex, with M. bovis identified in four cases.
Animal
In Austria, bovine tuberculosis is classified as a notifiable animal disease. Since 1999, Austria has been recognised as free from bovine tuberculosis. From May 2000, the nationwide screening of ruminants using the tuberculin test was discontinued; monitoring of the disease is now carried out as part of ante-mortem and post-mortem inspections.
Since 2008, in certain areas of the federal states of Tyrol and Vorarlberg, the use of the same pasture land during the grazing and alpine grazing seasons has led to the transmission of M. caprae infection between red deer and cattle. To assess the situation within the cattle population, special investigation and surveillance zones (in accordance with the Bovine Tuberculosis Ordinance) are therefore officially designated annually in these regions. In these areas, cattle are tested for tuberculosis before and after the alpine grazing period using a tuberculin test (simultaneous test). These tests are adapted to the established epidemiological situation and, where necessary, the areas covered are adjusted accordingly.
In 2025, the National Reference Laboratory for Bovine Tuberculosis identified the bovine tuberculosis pathogen M. caprae (Lecht genotype) in two cattle from two holdings in Tyrol (Landeck district) and in 33 animals from ten holdings in Vorarlberg (Bregenz and Bludenz districts). This pathogen was also detected following abnormalities found during post-slaughter meat inspection in four animals from Tyrol (Reutte and Landeck districts) and in two animals from Vorarlberg (Bludenz and Bregenz districts). Infection with M. caprae has thus been confirmed at a total of six holdings in Tyrol and 12 holdings in Vorarlberg.
Specialist Information on Human Medicine
People who have been in close contact with patients with active (i.e. infectious) pulmonary tuberculosis over a prolonged period are particularly at risk. In recent years, there has been an alarming increase in multi-drug-resistant strains of tuberculosis (i.e. strains that are resistant to at least the two most important anti-tuberculosis drugs, isoniazid and rifampicin). These are particularly prevalent in high-incidence regions such as Eastern Europe, Central Asia and parts of Africa and South-East Asia.
Following infection via respiratory droplets, small foci of inflammation usually form in the lungs within the following weeks, which encapsulate to form nodules (tubercles) (= primary infection). As the disease progresses, a distinction must be made between two possible conditions:
- Latent tuberculosis infection: The pathogens are present in the body but are kept in check by the immune system. There are neither symptoms nor any risk of transmission. Around 5–10 per cent of those with latent infection go on to develop active tuberculosis during their lifetime.
- Active tuberculosis: The pathogens multiply, leading to clinical symptoms and the potential to transmit the infection.
Active tuberculosis usually begins with non-specific general symptoms such as night sweats, low-grade fever or fever, fatigue, weight loss, loss of appetite and a general feeling of being unwell. In the most common form, pulmonary tuberculosis, tissue destruction can lead to the formation of so-called cavities (hollows) in the lungs. A characteristic feature is a persistent cough, often accompanied by bloody sputum. These patients are highly contagious (= active tuberculosis). Less commonly, the bacteria spread outside the lungs (extrapulmonary tuberculosis), as in the case of tuberculous meningitis (inflammation of the meninges). The term ‘miliary tuberculosis’ is used when there is a disseminated infection affecting several organs, usually involving the lungs.
The aim of any tuberculosis diagnosis is to culture the pathogen. Only this allows for further resistance testing and is a prerequisite for molecular typing and sequencing as part of outbreak investigation.
Due to the potential risk posed by the Mycobacterium tuberculosis complex, a specialised laboratory with biosafety level 3 (BSL-3) is required. Due to the slow growth rate of the pathogens, samples are incubated for up to eight weeks. Molecular biological methods such as nucleic acid amplification techniques (NAT) enable faster pathogen detection and provide early indications of resistance mutations in the pathogen.
Tuberculin skin test (TST):
The tuberculin skin test, based on the Mendel-Mantoux method, is used to detect an immunological response by the body to Mycobacterium tuberculosis, i.e. previous exposure to the pathogen. This test assesses the skin’s reaction to injected pathogen components; a positive reaction occurs no earlier than six weeks after infection. However, the test cannot distinguish between latent and active tuberculosis. Due to its limited specificity – particularly as a result of cross-reactions following prior BCG vaccination or in the case of non-tuberculous mycobacteria (NTM) – it is increasingly being replaced by the more specific interferon-γ release assays (IGRA).
Interferon-γ release assay (IGRA):
The IGRA test is a blood test and is also used to detect a past infection with Mycobacterium tuberculosis. It is now regarded as the diagnostic method of choice for identifying latent tuberculosis. The test becomes positive approximately 6 to 8 weeks after initial exposure to the pathogen.
In the IGRA test, the test subject’s blood is incubated in a blood collection tube coated with Mycobacterium tuberculosis-specific antigens (ESAT6 and CFP10). If the test subject’s immune system has been sensitised to tuberculosis bacteria (i.e. they have previously been in contact with tuberculosis pathogens), stimulation of the relevant T-lymphocytes leads to the production of interferon-gamma, which is then measured. You do not need to fast before the blood sample is taken. Special blood collection tubes (four QuantiFERON tubes) are used to carry out the test; each must be filled with 1 ml of blood. After the blood has been drawn, the tubes must be swirled 10 times. Alternatively, the blood can initially be collected in standard lithium heparin tubes. In this case, the blood is subsequently transferred to the four QuantiFERON tubes in the laboratory. The samples must be transported to the laboratory within 16 hours of blood collection at room temperature (22 °C ± 5 °C). The samples are then incubated at 37 °C for 16 to 24 hours and can be stored at 4–27 °C for up to 3 days prior to centrifugation. After incubation, the tubes are centrifuged and can be processed further or stored at 2–8 °C for a maximum of 4 weeks.
The method is primarily used to detect latent tuberculosis infection in individuals who have been in contact with someone with active pulmonary tuberculosis (contact tracing), for screening individuals from high-endemic areas (regions with a high prevalence of tuberculosis), and prior to the start of immunosuppressive therapy to rule out latent tuberculosis, as this can reactivate during treatment.
As with the tuberculin skin test, the IGRA test is also unable to distinguish between a latent infection and active disease.
A positive result therefore suggests past exposure to the pathogen, but does not provide any information about disease activity or the need for treatment, and always requires further diagnostic investigation. The diagnosis of active tuberculosis is usually made by detecting the pathogen via microscopy, molecular biological methods and culture, as well as clinical and radiological assessment.
A negative result rules out infection.
The IGRA is not suitable for monitoring treatment progress, as it may remain positive even after successful treatment.
Imaging techniques:
X-ray diagnostics can identify characteristic findings of pulmonary involvement; however, in terms of differential diagnosis, some other lung diseases cannot be definitively ruled out. Therefore, the diagnosis of tuberculosis is usually confirmed by a combination of several investigative procedures.
Bacteriological diagnostics:
The detection of mycobacterial nucleic acid provides an initial result within hours. The time-consuming culture-based detection of Mycobacterium tuberculosis complex (MTC) bacteria confirms the diagnosis of tuberculosis. The advantage of culture-based detection lies in the ability to test the mycobacteria for their susceptibility to specific antimicrobial drugs (resistance testing) and to type the isolates obtained using molecular biology.
Molecular diagnostics:
In accordance with the latest standards, samples are analysed using whole-genome sequencing (WGS). This enables matching strains to be identified and chains of infection to be traced epidemiologically. In addition, WGS enables the detection of further resistance genes and facilitates species classification within the Mycobacterium tuberculosis complex.
Specialist information for veterinary medicine
The causative agents of tuberculosis in humans and animals are closely related mycobacterial species, which are summarised as the Mycobacterium tuberculosis complex. This complex comprises the described species Mycobacterium (M.) tuberculosis, M. africanum, M. canettii, M. bovis, M. caprae, M. pinnipedii (seals), M. mungi (mongoose), M. orygis (antelope), M. suricattae (meerkat), Dassie Bacillus (rock hyrax) and M. microti (mice, secondary hosts e.g. cats, red deer, wild boar, camelids, cattle).
Chronic pulmonary tuberculosis in cattle mainly manifests itself in a progressive cough and slowly worsening general condition. However, disease processes can also occur in other organs. In cattle, tuberculosis can remain latent or subclinical for years.
In red deer, tuberculosis is a chronic disease. Clinical symptoms, if present, are often non-specific. The route of infection is usually oral or aerogenic. If the disease generalises to the head, thorax or abdomen, pathogens can be excreted in large quantities and - with the potential for transmission to other animal species - contaminate the environment. Winter feeding of wild animals is problematic: transmission is encouraged by pathogen transmission and lower natural mortality as well as the accumulation of animals in the feeding area.
Diagnostics in animals
Early detection of infected cattle is an important point in the fight against bovine tuberculosis and depends on in vivo tests such as the tuberculin and ɣ-interferon test. In Tyrol and Vorarlberg, cattle in certain risk areas for infections with M. caprae (special testing and monitoring areas) must be tested annually using a tuberculin test (simultaneous test). In addition, a blood test (ɣ-interferon test) can also be carried out. If the test is not negative, the cattle are killed for diagnostic purposes. A direct examination of tissue samples using PCR for MTC pathogens enables a rapid diagnosis.
Camelids can also be tested for MTC disease using a tuberculin test. A subsequent antibody test increases the detection rate of infected animals.
Tissue samples from red deer killed during hunting are also analysed for the presence of the bovine tuberculosis pathogen M. caprae and other mycobacteria of the MTC using PCR and bacterial culture. The selection of the animals to be sampled is based on a sampling plan.
The identification of the MTC species and genotyping of the culturally isolated bacterial strains is carried out using various molecular biological methods (RD4 PCR, DNA strip technology, MIRU VNTR analysis, WGS). Due to the classification as a risk group 3 pathogen, the cultivation of tuberculosis pathogens may only be carried out in the safety level L3 laboratory, the Centre for Biological Safety at the National Reference Laboratory for Bovine Tuberculosis in Mödling.
Contact
Leitung
Priv.-Doz. Mag. Dr. Alexander Indra
- humanmed.wien@ages.at
- +43 50 555 37111
-
Währingerstraße 25a
1090 Wien
Institut für veterinärmedizinische Untersuchungen Mödling
- vetmed.moedling@ages.at
- +43 50 555 38112
-
Robert Koch-Gasse 17
2340 Mödling
Last updated: 19.08.2026
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