An insight to Tuberculosis
Tuberculosis (TB) is a potentially life-threatening infectious disease caused by the bacterium, Mycobacterium Tuberculosis. It runs a history of more than 1000 years. M. tuberculosis primarily infects the lungs. But with progression or following repeated attacks, it can virtually affect any organ of your body including even the brain.
TB infections are classified as primary TB, post-primary TB / secondary TB according to their pathogenesis. In primary TB the pathogen infects your lungs. In post-primary or secondary TB, it may infect any part of the body, in addition to the lungs.
TB Mode of transmission
The respiratory secretions of infected people contain the pathogen. When such a person coughs or sneezes or talks, bacteria are released to the air in tiny droplets. Once another person inhales them in, the bacteria infects his lungs.
How the infection occurs? / pathophysiology of TB
Once M. tuberculosis settles in your lungs, it forms a structure called a granuloma. A TB granuloma is a small collection of immune cells and bacteria, hidden inside the lung tissue. This is also called a Ghon focus. In most of the immune-competent people, the infection settles at this stage while the pathogen being restricted to the Ghon focus. Later the Ghon focus may undergo calcification and appear as a whitish, small mass inside the lungs on the chest X-Ray.
In some people, particularly if they are immune-deficient, M. tuberculosis spread beyond the level of the Ghon focus. It enters the blood and disseminates throughout the body. The infected organs undergo tissue destruction with granuloma formation. This is called the Miliary TB, a result of progressive primary TB. In some of the infected people, the immune system may partly interrupt the pathogenic progress of M.tuberculosis. In such instance, bacterial seeding occurs only to one or two organs of the body and they remain dormant inside those organs. Later, following an immune deficiency, the infection arises from those organs with or without simultaneous lung infection. This is called as post-primary or secondary TB.
Reactivation of the Ghon focus in secondary TB, leads to lung destruction and cavitation. This can also occur as a result of reinfection by a more virulent subtype of the pathogen. Usually, in post-primary TB, infection is confined to the tissue that it originates from and rarely disseminates through the blood causing miliary TB.
The organs commonly affected by tuberculosis
- Liver and intestines – As a consequence of swallowing infected respiratory secretions
- Vertebral column and bones
- Salivary glands
- Meninges and brain
Symptoms of tuberculosis infection
The common symptoms of pulmonary TB are listed below. However, the symptoms may differ according to the infected organ.
- Chronic cough is the characteristic feature of pulmonary TB. Especially if the cough is lasting more than 3 weeks
- Bloodstained sputum
- Chest pain
- Night sweats
- Unexplained weight loss and loss of appetite
TB of the vertebral column usually presents as long-lasting backache. Intestinal TB is a very serious condition and such patients may present with abdominal pain, rectal bleeding and even constipation due to intestinal obstructions. Cerebral TB and TB meningitis may manifest as long-standing headaches, seizures (fits), changes in the behavior, etc.
Tuberculosis Risk factors
- HIV infection – current guidelines suggest to screen each and every patient diagnosed to have Tuberculosis, also for HIV.
- Other diseases that affect your immune system including diabetes
- Organ transplants – Medications are given to suppress the immune system.
- Certain drugs that affect the immune system
- Advanced age
- Exposure to a TB patient
Diagnostic tests for TB
Mantoux test – This test is used as a screening test for the diagnosis of TB. Several other infections (e.g.- leprosy), previous exposure to TB and even B.C.G vaccination may give false positive results. Immunodeficiency may give false negative results as well. Therefore, those who have positive results and those who have negative results, but suspected to have TB, should undergo further investigations for the diagnosis.
- Blood culture for acid fast bacilli,
- Identification of pathogen in sputum under light microscopy using special stains
- Chest X-Rays for characteristic lung signs (Ghon focus, Cavitations) are classical methods of diagnosis of active infection of M. tuberculosis
In addition to those tests, rapid diagnostic tests are available, but at a higher cost.
TB patients are treated with anti-TB medications. 1st line therapy consists of 4 main drugs, Isoniazid, Rifampicin, Pyrazinamide, and ethambutol. The therapy should be initiated by a clinician after a proper evaluation. But the duration of the treatment varies from 6 months to 9 months depending on the site of infection. Adherence to the therapy is extremely important. Non-compliance to the Anti-TB therapy leads to drug resistance. Currently it’s an emerging problem worldwide since there are strains of M. tuberculosis that do not respond to any type of available Anti-TB medications.
Prevention in Tuberculosis
- Wear masks if you travel to an area endemic of TB
- Cover your mouth when you cough or sneeze
- Adhere to the therapy if you are diagnosed to have TB
- Open the windows of the home for proper ventilation
- Vaccination of your newborn child within 24 hours of birth – B.C.G. vaccination.
Some further good reads