Tuberculosis (TB) is a highly infectious disease that is caused by strains of bacteria that belong to the Mycobacterium tuberculosis complex. Though TB mainly affects the lungs, it could also affect other parts of the body. A person is diagnosed with pulmonary tuberculosis, when the lungs get infected. Pulmonary tuberculosis is the most common form of tuberculosis. Bacteria that cause tuberculosis could also spread from the lungs to other parts of the body through blood or the lymph fluid.
An active TB disease of the lungs, airways, or larynx is considered to be highly contagious. Factors that are associated with contagiousness include the presence of cough and cavity in lungs. The causative bacteria can spread to others when a person affected by pulmonary tuberculosis disease coughs or sneezes. Under such circumstances, the bacteria become airborne. Inhalation of these airborne respiratory secretions or the use of personal belongings of the infected individual can cause the pathogen to spread to others.
Latent TB Infection Vs. Active Tuberculosis
It must be noted that not everyone who inhales these airborne secretions will develop tuberculosis. In case of healthy individuals, the immune system fights off the bacteria and prevents them from multiplying. However, bacteria may remain in a dormant state in the body. Mantoux tuberculin skin test is one of the diagnostic tests that can help to determine if a person has been exposed to the causative bacteria. If the test is positive, but the patient doesn't exhibit any symptoms, then he/she is diagnosed with a latent tuberculosis infection. It is believed that people who are affected by a latent tuberculosis infection cannot spread the causative bacteria to others.
On the other hand, transmission of tuberculosis can occur due to contact with people affected by active tuberculosis. Immunocompromised individuals are definitely more susceptible to developing active tuberculosis disease. An active TB disease can be diagnosed with the help of blood tests, culture testing, skin test, X-ray examination, sputum analysis, etc.
The characteristic symptoms of an active pulmonary TB disease include:
- Cough that lasts 3 weeks or longer (with or without blood or mucus)
- Unexplained weight loss
- Night sweats
- Loss of appetite
The clinically significant stages of tuberculosis include:
Primary Pulmonary Tuberculosis
This refers to the initial infection. It is characterized by a subpleural granuloma accompanied by an enlarged lymph node. In case of healthy individuals, the immune system fights against the bacteria, thereby preventing the progression of the disease. However, the immune system may not be able to completely eliminate the bacteria.
Secondary (Reactivation) Pulmonary Tuberculosis
Reactivation of a previous, subclinical infection could occur if the immune system gets weakened. More often than not, the upper lobes of the lungs are affected.
Progressive Pulmonary Tuberculosis
Though primary and secondary tuberculosis can resolve with medical treatment, in case of immunocompromised individuals, the initial infection could be followed by tuberculous pneumonia, miliary tuberculosis (disseminated form of tuberculosis), or cavitation.
Tuberculous pneumonia is a complication of tuberculosis that is characterized by a progressive lung infection. People with a compromised or weak immune system are more prone to getting infected with this disease. Young children, elderly, and people affected by HIV are more susceptible to it. The common symptoms include high fever and persistent cough (with or without blood).
Repetitive chest X-rays may be required to diagnose this condition. The characteristic sign of this condition is the appearance of small-sized granulomas throughout the lungs. Other symptoms include high fever, sweat, gradual weight loss, and a general decline in health.
Mycobacteria have the capacity to cause extensive damage to the upper lobes of the lungs by forming large cavities in it. This provides a highly oxygenated environment for bacteria to thrive in. The infection tends to spread into the pleural space as well, increasing the risk of complications. Symptoms include chronic cough (with or without blood), night sweats, low-grade to high fever, gradual weight loss, and fatigue.
Extrapulmonary tuberculosis is said to occur when the infection affects the bones, joints, pleura, lymph nodes, meninges, bowel, peritoneum, pericardium, or the genitourinary system. Extrapulmonary TB is less likely to be contagious, with the exception of laryngeal TB. However, at times people with extrapulmonary TB may also have pulmonary or laryngeal TB. Under such circumstances, the infection can spread to others through person-to-person contact.
The use of drugs such as isoniazid, rifampicin, pyrazinamide, or ethambutol can help in alleviating the symptoms of TB, if the drugs are taken as per the prescribed dosage for the duration recommended by the doctor. It's also extremely essential to follow precautionary measures to minimize the risk of transmission of the bacteria to others.
Disclaimer: The information provided in this article is solely for educating the reader. It is not intended to be a substitute for the advice of a medical expert.