Tuberculosis is a disease caused by a bacterium called ‘Mycobacterium tuberculosis’. This bacteria usually infects the lungs but can infect any part of body.

All those who get the infection don’t develop the disease and this is called Latent TB infection (LTBI). Only upto10% of all having the infection develop the active disease-what we call Tuberculosis disease. 

There are certain factors that make some people more prone to develop the disease than others. Tuberculosis can involve any part of the body like bones and brain but mainly affects the lungs.

Types of TB

Following the infection when bacteria causing tuberculosis enter the body, it can cause:

1. Latent TB:
   • when bacteria remain inside the body in a dormant state and don’t cause any disease. These people look normal and cant transmit the disease to others.
   • It is seen in people with good immune systems
   • Bacteria may become active as and when the environment supports like whenever the immunity of the person goes down
   • In India around 40% population is already having latent TB.
2. Active TB:
   • When the immune system of the body is not able to contain the bacterial multiplication to cause the disease.
   • These are the patients who present with symptoms and can transmit the disease to others.

Depending upon the response to antibiotic treatment, TB Patients can be:

1. DSTB: Drug-sensitive TB. Such patients respond well to all first-line antibiotics used to treat the TB
2. DRTB: Drug-resistant TB. Those patients who don’t respond to one or more than one First line antibiotic used to treat TB. It may further be classified into:
   1. Mono drug-resistant TB– Resistance to only one first-line anti-TB Drugs
   2. Polydrug-resistant TB– Resistance to more than one first-line anti-TB Drugs but not the  combination of Rifampicin and Isoniazid
   3. MDR– Mutlidrug-resistant TB. Resistant to Both Isoniazide and Rafampicin
   4. Pre-XDR TB: Pre-Extensively Drug-resistant TB. A patient is known to suffer from pre-XDR TB if he/she fits into either of the two parameters given below⁶:

5. XDR TB: Extensively Drug-Resistant TB. A patient is known to suffer from pre-XDR TB if he/she fits into either of the two parameters given below⁶:

Depending upon the site of infection:

1. Pulmonary TB: TB of the lungs. it is the most common among all.
2. Extrapulmonary TB: TB of body organs other than lungs.
   • not very common.
   • it may include the pleura of the lungs, lymph nodes, genitourinary tract, joints and bones, spine, kidney, meninges of the brain, intestine etc.

A patient with both pulmonary and extrapulmonary TB should be classified as a Pulmonary TB patient.

Transmission

Humans are the only reservoir of this bacterium, meaning it transmits from humans to humans.

Patients with tuberculosis of the lungs (pulmonary TB) or throat (laryngeal TB) can spread the infection to others via tiny droplets released when such patients cough, sneeze, laugh or sing. Such tiny droplets can remain suspended for hours in the air and a healthy person can get infected by inhaling them. It is important to note a few points here:

• Only Pulmonary and laryngeal tuberculosis is transmitted from patients to others. once the treatment is started, the patients become non-infectious within 2-3 weeks and don’t transmit the disease.

• Tuberculosis in other parts of the body (like the brain, bone, intestine etc.) is not transmissible.
• Although TB is contagious, it doesn’t spread easily. It usually takes longer contact time to catch the infection from TB Patient

Check out what doesn’t spread TB.

Another form of TB known as Bovine TB caused by Mycobacterium bovis can transmit from animals to humans but it is very rare.

Symptoms

As we know TB can occur in any part of the body. There are certain symptoms that are usually common to TB irrespective of the site of infection:

• Fever (usually low-grade)
• Loss of body weight
• Chills
• Night sweats
• Loss of appetite
• Generalised weakness- easy fatigability 

Symptoms specific to TB lungs: (In addition to the symptoms listed above)

• Chest pain
• Cough for more than 3 weeks (in India: more than 2 weeks)
• Blood in sputum
• Difficulty in breathing

Symptoms specific to TB Brain:

• Sick look
• Headache (severe)
• Feeling confused
• Neck rigidity
• Sensitivity to light 
• Vomiting and feeling of vomiting (nausea)

Symptoms specific to Bone/joints (most common is TB spine)

• Stiffness of joints
• Bony pains
• Severe Back Pain (TB Spine)
• Difficulty in walking or moving
• Soft tissue swelling around the bone and sometimes abscess formation