There are many subgroups in the genus mycobacterium such as M aviumintracellulare, M kansasii, M bovis, but M tuberculosis alone is pathogenic in human. Mycobacterium tuberculosis, most commonly affects the lungs. It is transmitted from person to person via droplets from the throat and lungs of people with the active respiratory disease. Most commonly, tuberculosis is caused by air-borne infection.
In healthy people, infection with Mycobacterium tuberculosis often causes no symptoms, since the person's immune system acts to “wall off” the bacteria. Most people who are exposed to TB never develop symptoms because the bacteria can live in an inactive form in the body. But if the immune system weakens, such as immunocompromised (HIV) or elderly adults, TB bacteria can become active and their active state causes death of tissue in the organs they infect. Active TB disease can be fatal if left untreated.
Tuberculosis is communicable infection of lung tissue (Pulmonary TB), and potentially other tissues (extrapulmonary or miliary TB).
Tuberculosis is caused by Mycobacterium tuberculosis, which spread from person to person through microscopic droplets released into the air. This can happen when someone with the untreated, active form of tuberculosis, coughs, speaks, sneezes, spits, laughs or sings.
Infection with TB requires inhalation of droplet nuclei. Following deposition in the alveoli, Mycobacterium tuberculosis is engulfed by alveolar macrophages, but survives and multiplies within the macrophages. Proliferating bacilli kill macrophages and are released; this event produces a response from the immune system. Exposure may lead to clearance of Mycobacterium tuberculosis, persistent latent infection, or progression to primary disease. Successful containment of TB is dependent on the cellular immune system, mediated primarily through T-helper cells (TH1 response). T cells and macrophages form a granuloma with a centre that contains necrotic material (caseous centre, Fig. 12.2). Mycobacterium tuberculosis, and peripheral granulation tissue consisting primarily of macrophages and lymphocytes; the granuloma serves to prevent further growth and spread of M.tuberculosis. These individuals are non-infectious and have latent TB infection; the majority of these patients will have a normal chest X-ray (CXR) and be tuberculin skin test (TST) positive .
During initial infection and granulomas, there are no symptoms of mild bronchial pneumonia but sputum test is positive.
In active TB, sign of chronic inflammation include:
- Overall sensation of feeling unwell
- Weight loss
- Low grade fever
- Night sweating,
- Coughing that lasts longer than 2 weeks with green, yellow, or bloody sputum
- Shortness of breath,
Treatment for TB depends on whether it is active or latent. Patient may be hospitalized or suggested to avoid contact with other people until tests show that the patient is not contagious.
Antibiotics: For TB lung infections, antituberculosis drugs eg. isoniazid, rifampicin, ethambutol, Pyrazinamide and streptomycin (Ist line) drugs are more effective. While para-amino salicylic acid, thiacetazone, ethionamide, cycloserine, kanamycin and rifabutin are IInd line drugs. A number of new drugs are available to overcome the current drug resistant combination treatment including: bedaquiline, delamanid, linezolid and sutezolid.
Vaccination: A vaccine is available to limit the spread of bacteria after TB infection: The vaccine is generally used in countries or communities where the risk of TB infection is greater than 1% each year. It is used in new borns in these communities to prevent TB and its complications in the first few years of life.
1. Education and screening: To reduce risk of infection and transmission, peoples with close contact with patient may undergo prophylactic therapy. To minimize air born infection use protective measures such as covering
mouth and nose when coughing. Do not spend long periods of time in stuffy, enclosed rooms with anyone who has active TB until that person has been
treated for at least 2 weeks. Someone who has active TB, help and encourage the person to follow treatment instructions.
2. Early diagnosis and treatment: TB should be treated early in order to prevent deterioration of the disease and spread of the infection.
3. Leading a healthy life style: The germs attack the lungs when a person's body resistance is reduced. Try to guard by leading a healthy lifestyle in order to minimize the chance of contracting the illness. This includes: adequate exercise, enough rest and sleep, balanced diet, avoidance of smoking and alcohol, breathing fresh air and maintaining good indoor ventilation.
4. BCG (Bacillus Calmette-Guerin) vaccination: The TB and Chest Service provides BCG vaccination to all new born babies to protect them against tuberculosis. TB germs are spread by: TB germs are spread through the air when a person, who is sick with TB disease coughs, sings, sneezes, or laughs. To become infected with TB germs, a person usually needs to share air space with someone sick with TB disease (e.g., live, work, or play together). The amount of time, the environment, and how sick the person is all contribute to whether or not get infected. In most cases, body is able to fight off the germs.