TB Medical Information

Definition

Tuberculosis is a chronic infection of the lungs or other organs through the mycobacterium tuberculosis. Infection rate, morbidity and mortality through tuberculosis are extremely high outside Industrialised Countries. After HIV, yet still ahead of plasmodium falciparum, the virus of tropical malaria, mycobacterium tuberculosis is worldwide the most significant cause of deadly infectious diseases.

Transmission

The transmission takes place as a rule through droplet infection from person to person. Through mycobacterium bovis, a close relative of M. tuberculosis, a tuberculosis of the intestines can also develop via infected cow milk.

Epidemiology

Approx. 2 billion infected persons worldwide are assumed; thus, a third of the world population carries the mycobacterium tuberculosis. 99% of them are, however, not afflicted, but are in the stage of „latent tuberculosis“. Annually, there are approx. 40 million new infections, out of which the majority roams freely without symptoms and leads to latent tuberculosis. Manifestly, approx. eight million persons get afflicted every year, the tendency is increasing by about 1% every year. Out of these, about 1,5–2 million persons die from the consequences of the affliction.

Poverty is regarded as an important promoting factor of tuberculosis. Seen globally and regionally, socio-economically poor countries and population groups are affected considerably more frequently than rich countries and prosperous classes of the population.

The driving force of the rapid rise of tuberculosis in the countries of Africa south of the Sahara is the co-infection with HIV. The weakened immune competence of the afflicted persons leads to quick activation of the latent tuberculosis as well as to quick contraction of a new infection.

Microbiology

Robert Koch discovered the mycobacterium tuberculosis in 1882. It is an acid-proof rod bacterium, which can be viewed through the special Ziehl-Neelsen-colouring. Mycobacterium tuberculosis belongs to the large family of partly „wild-living“ mycobacteria. It is a case of obligatory aerobic parasites with only limited ability to survive outside the host. They do not form any spores and grow only extremely slowly on special culture medium (Löwenstein-Jensen-Agar).

Pathogenesis

After the infection with M. tuberculosis through infected spit droplets, the respiratory tract reacts with the formation of a "primary complex" in the lung and subsequently with a direct lymphogenic or haematogenic spread of the virus. Decisive for the further progression of the disease of the affliction is the competence of the cell-mediated immunity.

Clinical Picture

Governing symptoms of the infection of the lungs are long-lasting chronic coughing. This symptom is so typical for tuberculosis of the lungs, that it is given first place worldwide as governing symptom during simplified diagnosing: „Cough lasting longer than three weeks – could be tuberculosis and must be examined accordingly“. It is accompanied by sputum, which could develop into blood cough (Haemoptysis). Significant is also the generalised decomposition of strength (cachexia) of the patients. In the clinical practice of the poor countries of the South, the frequency of extra-pulmonary manifestation is also important. There, the appearance of diverse tuberculosis-induced pictures of the affliction can be expected: lupus vulgaris of the skin, meningitis tuberculosis, cervical lymph node tuberculosis, TB pleuritis and TB pericarditis exsudativa, tuberculosis peritonitis and tuberculosis of the intestine, urogenital tuberculosis, the affliction of the vertebrae with hunch formation (pott-gibbus), tuberculosis of the long hollow bone and the large joints. The most serious form of progression of tuberculosis is the miliary form, this corresponds to a sepsis-like spread of the virus in the entire body, due to the lack of cell-mediated defence. Miliary tuberculosis is observed increasingly in small children with immune system, which is still weak, besides, it is found frequently in cases of co-infection with HIV or measles. Miliary tuberculosis leads to death even when there is appropriate treatment.

Diagnosis

The microscopic analysis of the sputum, which identifies the infected patients with a high degree of accuracy, is still regarded as the key analysis in tuberculosis control. This analysis also supplies the proof of the virus. Patients with low germ count in the sputum are often overlooked, yet, they also exhibit a comparably high rate of spontaneous healing.

The analysis of bacteriological sputum cultures is the diagnostic method, which supplies the most reliable proof,it is deemed to be the „gold standard“ of TB diagnostic. A resistance test of the virus can also be conducted by means of bacteriology. The high costs and the considerable delays before the presentation of a final result, however, prevent its application as diagnostic in clinical routine.

If meningeal tuberculosis is suspected, the spinal fluid can be examined, also contusions of the visceral cavities (pleura, abdomen, heart, joints) can be punctured and the obtained puncture can be analysed for mycobacteria.

Pulmonary tuberculosis indeed leads to regular changes in the x-ray of the thorax. These changes, however, are surprisingly unspecific. In extensive analyses, the results differ even among experienced radiologists to a considerable extent, with the result that x-ray diagnosis does not represent the means of first choice. It does not deliver any specific diagnosis, but can help during the evaluation of the healing process.

Therapy

For many centuries, the therapy of tuberculosis was limited to the administration of antibiotics known for a long time. Only in the past five years, triggered by the dramatic rise in tuberculosis worldwide, a new wave of research has started, which has the objective of putting forth new and more effective drugs. The treatment of tuberculosis is largely standardised worldwide. No other infectious disease has brought about such a high level of worldwide equalisation of therapy procedures as tuberculosis.

Within the framework of the DOTS strategy, a possibly short, but adequately effective ambulant treatment under temporary direct observation of the drug ingestion is recommended („Directly Observed Treatment – Short Course“). In order to prevent a resistance development, DOTS is undertaken with several effective drugs simultaneously. The known drugs for the standard treatment of tuberculosis are isoniazid, rifampicin, pyrazinamide as well as ethambutol and streptomycin. Thioacetazone has disappeared from treatment plans, since it can trigger serious side effects in HIV positive tuberculosis patients. The duration of the standard treatment is six to eight months, as a rule with an intensive phase lasting two months, during which rifampicin is always administered in addition to another three drugs. The subsequent phase of treatment lasting four to six months is undertaken with only two more drugs (4 months with rifampicin and isoniazide or six months with ethambutol and isoniazide).

Fresh hope through new developments

Since the start of the new millennium a lot of money has been invested in the development of improved medication. Due to this, it is expected that the standard treatment is going to change significantly by 2015, in order to lead a more successful fight against resistant bacteria. Another ray of hope is the introduction of new vaccines. However these new developments are not going to be largely applicable before 2020.

Tuberculosis and Public Health

From the point of view of public health, it is important to detect and treat the infectious, „exposed“ TB patients as early as possible. They are the source of the spread of the disease. They constitute as a rule about 40 – 60% of the tuberculosis patients of a country. From the point of view of the individual patient, it is important to reduce and heal suffering, irrespective of the risk of infection of other persons. Both these principles fail to converge in many tuberculosis programmes of poor countries, where the resources for an equally good care of infectious and uninfectious patients are lacking. Often, children with tuberculosis and the so-called „smearnegative“ pulmonary and non-pulmonary patients are neglected.

The most important measure for the reduction of the frequency of infection is not the vaccination against tuberculosis, „BCG“ (Bacille Calmette-Guérin), which is available up to now.BCG prevents serious progressions of tuberculosis in childhood, but has no influence on the development of latent to active tuberculosis in adulthood. Exposure prophylaxis in the environment of active victims with isoniazide is effective both in the case of children as well as in those with weak immune systems (e.g. through HIV).