Synonyms in the broadest sense
Consumption, Koch's disease (based on the discoverer Robert Koch), Tbc
Definition of tuberculosis
Tuberculosis is an infectious disease caused by bacteria belonging to the class of mycobacteria.
The most important representatives of this group are Mycobacterium tuberculosis, which is responsible for over 90% of the diseases, and the mycobacterium bovis, which is responsible for the majority of the remaining 10%. The latter is important in that it is the only mycobacterium able to survive in an animal host.
There are around two billion (!) People worldwide who are infected with the bacterium infected, with the main focus in Africa and the former Eastern Bloc countries. This makes tuberculosis the most common infectious disease. Around eight million people die of tuberculosis each year, which is a small number compared to the number of people infected (low mortality). In Germany there are currently fewer than 10,000 sick people, although the number of those infected has been falling continuously for several years.
Causes of Tuberculosis
The bacterium is usually (in more than 80% of all cases) transmitted by droplet infection (saliva) from human to human. Other routes of transmission via the skin (only if the skin is injured), urine or faeces are possible, but are the exception. If cows are infected with the pathogen Mycobacterium bovis, they can infect humans through their raw milk. However, tuberculosis disease in cattle has been eradicated in western countries and the risk of contracting tuberculosis through milk consumption has been eliminated.
If a healthy person has contact with the bacteria, he can fight off the disease in about 90% of the cases. In other words: the infectiousness of the pathogen is low. In people with immunosuppression (worsened immune system, for example AIDS patients, alcoholics, severe diabetes mellitus disease, malnourished people), the risk of infection is significantly higher. Tuberculosis is the leading cause of death for people infected with HIV!
Mycobacteria are characterized by the fact that, in addition to the normal structure of a bacterium with a cell wall, they are also surrounded by a thick layer of wax. This wax layer is the reason for the numerous special features:
- The exchange of nutrients with the environment (diffusion) is severely restricted. This is the reason why tuberculosis can only be combated with difficulty with antibiotics (special drugs that are quite selective against bacteria), because they too have to get into the cell in order to be able to develop their effect.
- Mycobacteria divide extremely slowly. While some bacteria, such as the Escherichia coli found in the intestine, have a generation time of 20 minutes (i.e. doubling every 20 minutes), the tuberculosis pathogen takes about a day. This in turn means that there is a long period of time (approx. Six weeks) between infection with the pathogen and the onset of the disease
- The immune cells (defense cells) of the human body, once they have infected the body, can only poorly recognize the bacteria and thus fight them poorly. On the contrary, mycobacteria can even survive in certain immune cells, so-called phagocytes, and spread throughout the body.
- Thanks to their wax layer, they can also survive in a strongly acidic environment (for example in gastric juice).
The human immune system fights bacteria in a special way. If the body's defense system does not manage to kill all the bacteria as it penetrates, the defense cells try to wall up the pathogens. This has the advantage that the bacteria cannot spread any further; however, there is also the disadvantage that they cannot be fought further within this structure. On the contrary, the pathogens can survive for years in this structure, also known as granuloma or tubercle, and trigger a new attack of the disease (endogenous reinfection, secondary infection) if the body's immune system deteriorates. Over time, these granulomas become calcified, which can be seen on a chest x-ray (chest x-ray).
Read more on the topic: Chest x-ray (chest x-ray)
In principle, tuberculosis bacteria can attack all human organs. Since the main route of infection for tuberculosis is inhalation, the lungs are also affected in more than 80% of cases. Other organs that are more frequently affected are the lungs (Pleura), the brain and the liver. If several organs are affected, one also speaks of miliary tuberculosis, because pea-like nodules in the affected organs can be detected with the naked eye (for example during operations or an autopsy).
You can find a detailed overview of all tropical diseases under the article: Overview page on tropical diseases
Diagnosis of tuberculosis
Because of the length of time between infection with the bacterium and the onset of tuberculosis (Latency period, incubation period) it is often difficult for the attending physician in the anamnese (medical history survey) to discover evidence of a tuberculosis infection. It is not uncommon for misdiagnoses to occur because the possibility of tuberculosis is not considered.
The diagnosis of the tuberculosis turns out to be quite difficult because there is no simple, reliably functioning test. Rather, one tries to increase the certainty of a correct diagnosis through several tests.
The first indications are possible contact with tuberculosis patients, for example through sick relatives, trips abroad to countries with a low socio-economic status (especially former Eastern Bloc countries) or signs of a reduced immune function of the body.
No typical values for or against tuberculosis can be determined in the blood test. Often there are signs of a general inflammatory reaction such as an increased ESR (sedimentation rate) or slight shifts in the blood count.
With the help of the so-called Tuberculin tests (Mendel-Mantoux test) is used to check whether the patient has ever had contact with mycobacteria. To do this, the patient is injected with tuberculin (a protein from the tuberculosis pathogen) into the crook of the forearm.
If the patient has been infected with the bacteria in the past, the injection site will be reddened and swollen within two to three days. If this swelling exceeds a certain level, an earlier infection is assumed. Possible false-negative results (infected people who are incorrectly not recognized) are often found if:
- the infection was less than seven weeks ago because the body is not yet able to trigger an appropriate immune response.
- the patient suffers from immune deficiency (HIV-infected, immunosuppressive (= immune-weakening to suppressive) treatment, leukemia).
- has recently been vaccinated.
A positive test is not indicative of tuberculosis, but at least it is a strong suspicion.
An X-ray of the patient's chest (chest X-ray) is now made. There you look for the typical signs of tuberculosis calcified granulomas in the lungs. However, the X-ray image does not provide any certainty either, as a negative finding does not exclude tuberculosis, nor does a positive finding prove tuberculosis.
The next step in diagnosing tuberculosis is to try to detect the bacteria directly. Various samples are obtained from the patient: urine, gastric juice, bronchial secretions by means of a lung specimen or saliva. One tries to grow the bacteria from this material. If the cultivation is successful, this is evidence of tuberculosis infection. Growing takes several weeks because of the slow growth rate of the bacteria.
This is problematic for two reasons:
- the patient has to endure a long period of uncertainty and
- the possible risk of spreading the bacteria must be considered.
In rare cases, an MRI of the lungs can provide information, as the MRI of the lungs can clearly show soft tissue processes within the lungs.
Read more about this at: MRI of the lungs