However some tubercle bacilli penetrate beyond the airways into the alveolar sacs of the lungs. Once there the bacilli are usually engulfed by alveolar macrophages cells, which are able digest bacterium. This is known as the process of phagocytosis.
Once inside the macrophages bacilli are subjected destruction via a number of responses.
- Phagosome-lysosome fusion
- Generation of reactive intermediates and nitrogen intermediates
However the tubercle bacilli resist this digestion and start multiplying inside the phagocytes. Some of these phagocytic cells may eventually migrate to the mucus layer where the bacilli are carried out of the body but other carry them to various parts of the lung, lymph of a nearby lymph nodes or even into the blood stream to other site e.g. lung apices, bone marrow, kidney, meninges.
Within several weeks of the initial exposure to infection, tubercle, a hard swelling, is formed in the alveolar sac, as macrophages containing the tubercle bacilli clump together. As these macrophages are joined by other white blood cells, the clump grows larger and destroys surrounding lung tissues. If cells inside the tubercle die, they form caseous, which supports the growth of tubercle bacilli. At the same time the tough scar tissue surround the tubercle and decrease the amount of oxygen and prevents further growth of the bacilli. These bacilli however remain alive but inactive.
In recent studies cytokines have, addition to activation of macrophages, proved to be able to kill Mycobacteria directly through cytotoxic T-lymphocyte activity.
Symptoms
Neither pulmonary nor extrapulmonary tuberculosis display any definite symptoms. In the past TB was called “consumption” because the sufferers appear as if they are “consumed” from within.
The following symptoms may be the only indication to the patient of the progression of Tuberculosis.
- Prolonged cough [more than 3 weeks]
- Cough sputum containing mucus, pus and/or blood
- Fatigue
- Weight loss
- Loss of appetite
- Night sweats
- Chills
- Fever
- Acute influenza like illness
- Rapid heart beat
- shortness of breath
- chest pain
- Erythema nodosum
- Swelling in the neck {when lymph nodes in the neck are infected}
Burning on urination
- Blood and white cells in the urine
Acute or chronic fever
- Headache
- Irritability
- Malaise
Diagnosis
As tuberculosis does not display any specific symptom it is quite hard for physicians to diagnose patients with the disease. Initial medical history of the patient is taken to find any suspected TB symptoms e.g. prolonged cough, loss of appetite, fatigue etc. Following medical history, upon physical examination of the lungs an experience doctor should identify the crackle noise in the chest, pleural effusion.
Tuberculosis should also be suspected when a persistent respiratory illness in an otherwise healthy individual does not respond to regular antibiotics.
If TB is suspected in a patient, doctors advice the tuberculin skin test. If positive this test indicates that the patient has been infected with the tubercle bacilli irrespective of time i.e. whether the TB is active or latent cannot be confirmed based on this test.
If the result of the skin test is positive, patient is sent for a chest x-ray. X-ray shows the presence of tubercle or any other signs of TB in the lungs.
The last and final test of diagnosis of pulmonary TB is a sputum smear. Sputum of the patient is strained with chemicals to make any bacilli visible. If presence of bacilli is found, it is then culturedto determine whether they are Mycobacterium tuberculosis or other bacilli. By doing sensitivity test on these culture doctors can also determine the most effective medicine against these bacteria. Even if the sputum smear is negative, TB can only be ruled out if the culture is also negative.
Culture, biopsy, CAT scan and MRI can diagnose extrapulmonary disease. For example:
- Biopsy of affected area is examined for TB causing bacteria
- CAT scan show whether miliary TB has spread through out the body
- MRI shows TB in the brain or spine
- Urine culture detects renal TB
- Cerebrospinal fluid is tested for Meningitis TB
Treatment
Until the mid 20th century, the sole treatment for TB was long period isolation in sanatoriums. It was believed that the clean, cold air, abundant food and enforced rest stopped the spread of the disease and healed the lungs. Sometimes this treatment reinforced not only to help cure the disease but also control it's spreading.
Even today there is no single specific cure for TB. New antibiotics are used to control and cure TB in a measured way. The exact drugs and length of treatment depends on the patients' age, overall heath, the results of susceptibility and whether they have the TB infection or active TB disease.
As the TB bacteria grows slowly, the treatment becomes and long and lengthy process, 6 to 12 months. After a few weak of medication, patient becomes non-contagious and starts to feel better. However it is very important that they continue with full course medicine as partial/ improper use of antibiotics may lead to multidrug-resistant TB bacteria, greatly reducing the chance of being cured.
