When a person suffering from tuberculosis, coughs, sneezes, talks, especially loudly, laughs, spits sputum, etc.
, he throws out in the air tiny droplets of sputum laden with tubercle bacilli, when the patient has not covered his face with a piece of cloth or handkerchief.
In this way, the air around the patient gets infected with enormous tubercle bacilli, grouped together in various tiny droplets of sputum.
Any person, in close proximity of the patient is likely to inhale these tiny droplets.
Many of these large size droplets may fall on the ground, and they may be inhaled later when they get dried and reduced in size further.
They may survive in the soil for as long as six months.
Hence the dust contaminated with tiny dried droplets of tubercle bacilli plays a great role in the transmission of the disease.
Even the area / room, where a patient of tuberculosis has been isolated, remains potentially contaminated, as tiny droplets of sputum float in the air there.
Tubercle bacilli-laden sputum, in tiny droplets, enter into the nose and go through the air passages, and finally reach the tiny air sacs of the lungs (alveoli.
Primary complex During the initial/primary infection, the tubercle bacilli start multiplying very slowly in the body.
Some remain in the air sacs (alveoli), while others enter the nearby / regional/hilar / mediastinal lymph nodes.
Provided the natural defense mechanism of the body is good, the lesions, as a result of invasion of tubercle bacilli, both in the air sacs/ alveoli or lungs, and in the glands, get healed and calcified.
These two healed/ calcified lesions, i.
e.
, in the lung, as well as in the glands, together, are called a primary complex.
It is understood that the patient will have hardly any symptoms during this infection.
It will be of interest to the readers to know that this primary complex is supposed to safeguard the person against future/ fresh infection of tubercle bacilli.
All persons in whom a primary complex has developed will be 'tuberculin skin test' positive, as the individual concerned would have developed hypersensitivity to the proteins of tubercle bacilli, known as 'tuberculins', which are used while performing this test.
It is an important test, and is primarily meant to detect initial infection or a primary lesion/complex in an individual.
This test has particular value in an epidemiological study to find out the infected cases of tuberculosis in a community, i.
e.
, 'tuberculin test surveys'.
In case the natural defense mechanism of the body is poor, following primary / initial invasion by tubercle bacilli, the patient may suffer from frank tuberculosis.
Sites of infection of tubercle bacilli However, in some cases, following primary infection by tubercle bacilli, the bacilli may also remain dormant in the body, even for the whole life of the patient.
This is the most dangerous situation, since the tubercle bacilli may become active at any time, say after one year or after many years, and start multiplying and triggering off the disease.
They truly act like potential enemies in the body, and attack whenever the defense mechanism of the body is on the lower side/ decreases.
However, they may never become active, if the defense mechanism/ resistance of the body remains strong.
Dormant tubercle bacilli The lungs are the most favorable sites for the multiplication/ growth of tubercle bacilli, as the bacilli find suitable conditions for their development, including a good supply of oxygen.
The kidneys, bones and brain are other places that favor the growth of tubercle bacilli.
The tubercle bacilli reach these sites through blood from their lesion in various lymph nodes.
Hence, tuberculosis may not occur in all organs of the body, as many organs/tissues may not be suitable for the growth of tubercle bacilli.